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Inheritance J23

Business Studies (The British International School of Jeddah)

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Inheritance and variation

Practice notes
Important questions

Dr. Nihal Gabr

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Biology 0610 Paper 4 Inheritance & variation

15 Page 9 October/november2011 Syllabus-0610 Paper 33

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Effect of humidity

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Biology 0610 Paper 4 Inheritance & variation

Skills

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Biology 0610 Paper 3 Inheritance & variation

20 Page 10 May/ June 2018 Syllabus-0610 Paper 43

4-

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Biology 0610 Paper 3 Inheritance & variation

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Biology 0610 Paper 3 Inheritance & variation

25 Page 7 October/november2013 Syllabus-0610 Paper 31

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Inheritance
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Biology 0610 Paper 3 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

Direct

Inheritance
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Page 8 October/november2011 Syllabus-0610 Paper 32

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Biology 0610 Paper 4 Inheritance & variation

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Variation
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Biology 0610 Paper 4 Inheritance & variation

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13

(iii) The doctors concluded that some diets reduce the risk of CHD.

Give evidence from Fig. 3.2 to support this conclusion.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

[Total: 23]

4 Forest ecosystems are threatened by many human activities.

(a) (i) Describe reasons why people cut down forests.

...........................................................................................................................................
Direct not taken yet
...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

(ii) Describe how forests can be conserved.

not taken yet

...........................................................................................................................................

...........................................................................................................................................
Direct ...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

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14

(b) Ecologists in one country were concerned that some mammals had been affected by
deforestation.

Fig. 4.1 is a diagram showing how deforestation affected one area of forest.

Key:
forest
cleared land

original forest

many trees were cut down

small forest area

remaining forest

large forest area

Fig. 4.1

The ecologists studied eight species of mammal. They recorded how many of the small and
large areas of the remaining forest contained each of the eight species.

Two species, the black rat and the house mouse, are not usually found in this forest
ecosystem. They were introduced to the area by humans many years ago before any trees
were cut down.

The other six species are known to live in this forest ecosystem.

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Table 4.1

percentage of small percentage of large

average body
species of mammal forest areas containing forest areas containing
mass / g
the species the species
house mouse* 18 46 - = 42
brown antechinus 40 62 - 83
swamp rat 130 15 25
bush rat 160 85 - 100
black rat* 200 15 0
southern brown bandicoot 850 31 ~ 92

⑧ 9
long-nosed potoroo 1100 8 17 =

long-nosed bandicoot 1300 8 25 =14

*introduced species :
(i) State which mammal in Table 4.1 showed almost no preference between small and large
areas of forest.

..................................................................................................................................... [1]

(ii) The ecologists made a hypothesis:

‘Larger areas of forest are better for the conservation of mammals.’

ranite
Discuss the evidence from Table 4.1 to support or reject this hypothesis.

...........................................................................................................................................

not taken yet

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................
Skills ...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [4]

[Total: 11]

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Biology 0610 Paper 4 Inheritance & variation

22 Page 4 October/november2012 Syllabus-0610 Paper 32

2-

Inheritance
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23 Cladogram design questions October/november2012 Syllabus-0610 Paper 33

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Inheritance

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

Variation
Direct

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24 Effect of mutation
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Inheritance

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Biology 0610 Paper 4 Inheritance & variation

16 Page 13 October/november2010 Syllabus-0610 Paper 32

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Biology 0610 Paper 4 Inheritance & variation

Direct

Linked to biotechnology( genetic engineering)

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Biology 0610 Paper 4 Inheritance & variation

Linked to biotechnology( genetic engineering)

Direct

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Biology 0610 Paper 4 Inheritance & variation

① Variation

Variation
①Due to mutation where there is a change in gene reulting in new alleles .
①Changes in environmental conditions acts as a Selection pressure
①Those have favorable characteristic are able to survive being better adapted
①While those with less fav. Ch. die

r
①Survival of fittest, where the better adapted will be able to reproduce and pass on

ab
①the favourable allele to the coming genertaions
①Increasing the frequency of allele coding for adaptive feature in the population

24 Effect of mutation
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October/november2012 Syllabus-0610 Paper 33
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Inheritance

Alternative form of gene

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

35 Genetic engineering October/November 2018 Meiosis &variation Paper 42

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Biology 0610 Paper 4 Inheritance & variation

37 Variation May/June 2019 Artificial selection Paper 41

Direct ⑪
①

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

38 Biotechnology May/June 2019 Genetic engineering Paper 43

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Ligase -

gene
.

Recombinant
DNA .

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

Skills

r
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Crops that are resistant to herbicide .....( soya bean )...kill weeds only thus
iha
increasing crop yield and quality by decreasing competition on minerals, water
and light .
.N

Crops that produce their own toxins....( cotton plants) ..less use of insecticides ,
Dr

avoid killing useful insects , less pollution , increase in crop yield and quality, less
money spent on insecticides , less chance for insects to become resistance .

Crops that are reach in nutrients such as golden rice rich in vitamin A
Increase nutritional value

Crops that are resistant to disease

Increase crop yield and quality

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Biology 0610 Paper 4 Inheritance & variation

39 Inheritance May/June 2019 Stem cells Paper 41

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

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Biology 0610 Paper 4 Inheritance & variation

40 Cell division March 2020 Stem cells Paper 42

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Biology 0610 Paper 4 Inheritance & variation

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18

6 Fig. 6.1 is a diagram of DNA.

Key:
base pair
base A

Fig. 6.1

(a) (i) State the letter of the base that pairs with A.

..................................................................................................................................... [1]

(ii) State the letters of the other bases in DNA.

..................................................................................................................................... [1]

(b) Outline the roles of DNA in a cell.

...................................................................................................................................................

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...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [2]

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(c) Fig. 6.2 shows a plant tissue in which cells are dividing by mitosis.

J
H

Fig. 6.2

(i) Cell H in Fig. 6.2 is about to divide by mitosis.

State what happens to the chromosomes in cell H before mitosis takes place and state
why it is necessary.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(ii) Cell K is about to divide into two cells.

State the structures that will form between the nuclei so that the cell divides into two
cells.

...........................................................................................................................................

..................................................................................................................................... [2]

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(iii) Cell J in Fig. 6.2 is an example of a diploid cell.

State what is meant by the term diploid.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

[Total: 9]

Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every
reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the
publisher will be pleased to make amends at the earliest possible opportunity.

To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge
Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download
at www.cambridgeinternational.org after the live examination series.

Cambridge Assessment International Education is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of the University of
Cambridge Local Examinations Syndicate (UCLES), which itself is a department of the University of Cambridge.

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6 Colour blindness is a characteristic that is inherited. Colour blindness is more common in males
than in females.

Fig. 6.1 is a pedigree diagram showing the inheritance of colour blindness in a family.

Key:
male with normal
colour vision
male with colour
blindness
1 2
female with normal
colour vision
3 4

5 6 7 8

Fig. 6.1

(a) Define the term inheritance.

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [1]

(b) (i) Using the symbols B and b, state the genotypes of individual 5 and individual 8 in the
pedigree diagram.

5 ........................................................................................................................................

8 ........................................................................................................................................
[3]

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(ii) Individual 3 is a carrier of colour blindness because she has one copy of the allele for
/

colour blindness but has normal colour vision.

Describe the evidence from Fig. 6.1 that shows that individual 3 is a carrier.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

(iii) There was no history of colour blindness in the parents and grandparents of individuals 1
and 2.

Suggest how colour blindness first occurred in the family in Fig. 6.1.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

[Total: 9]

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3 The American writer Ernest Hemingway lived on the island of Key West in Florida, USA in the
1930s. During this time he was given a male cat by a sea captain.

The cat had more toes than usual. This inherited condition is called polydactyly. The allele for
polydactyly is dominant.

(a) Define the term inheritance.

Transfer of genetic material from generation to another

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [1]

(b) Fig. 3.1 is part of a pedigree diagram for Hemingway’s cats.

-

-t
1 2

3 4 5 6 7 8 9 10

11 12 13 14 15 16

Key:
17
female cat with normal female cat with
number of toes polydactyly

male cat with normal male cat with

number of toes polydactyly

Fig. 3.1

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(i) State the genotypes of cats 5, 6 and 14 in the pedigree diagram in Fig. 3.1.

Use the letters T and t.

cat 5 ..................................................................................................................................

cat 6 ..................................................................................................................................

cat 14 ................................................................................................................................
[3]

(ii) Explain why none of the offspring of cats 3 and 4 have inherited polydactyly.

Use the information in Fig. 3.1 in your answer.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

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(c) Scientists published the results of an investigation into the DNA of cats with and without
polydactyly. They compared the base sequence from a particular region of DNA that controls
the development of the limbs.

Table 3.1 shows the base sequences.

t
Table 3.1

cats without polydactyly AGA CAC AGA AAT GAG

Hemingway’s cats with polydactyly AGA CAC GGA AAT GAG
cats with polydactyly from Oregon and Missouri in the USA AGA CAC GGA AAT GAG
cats with polydactyly from the UK AGA CAC AGT AAT GAG

(i) Describe how the base sequences of the cats with polydactyly differ from the base
sequence of cats without polydactyly.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(ii) State the name of the process by which base sequences in DNA are changed.

..................................................................................................................................... [1]

(iii) The base sequences in Table 3.1 provide evidence that indicates which country the male
cat given to Hemingway in the 1930s came from.

Suggest which country this cat came from and give a reason for your choice.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

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(d) Fig. 3.2 shows part of a DNA molecule from a chromosome of a cat.

Complete Fig. 3.2 by writing the letters for the base sequence of the other strand of the DNA
molecule.

T ..........

A ..........

A ..........

T ..........

G ..........

C ..........

G ..........

T ..........

G ..........

Fig. 3.2
[1]

(e) Explain why polydactyly is an example of discontinuous variation.

...................................................................................................................................................

...................................................................................................................................................

⑪
...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [2]

[Total: 13]

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3 Cheetahs, Acinonyx jubatus, are carnivores found in the dry grasslands and woodlands of
southern Africa. Cheetahs hunt for food during the day. They eat deer and antelope.

The cheetah is the fastest mammal on land but can only run at high speed (sprint) over a short
distance. Its hunting strategy is to creep up on prey and then sprint to catch them.

Fig. 3.1 is a photograph of a cheetah in its natural habitat.

Fig. 3.1

(a) Suggest how these adaptive features enable cheetahs to survive in their natural environment.

fur colouring ..............................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

streamlined body shape ...........................................................................................................

...................................................................................................................................................

...................................................................................................................................................
[2]

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(b) The king cheetah is a rare variety of A. jubatus that has inherited striped fur markings.

Fig. 3.2 shows a cheetah with spots and a king cheetah.

cheetah with spots king cheetah

Fig. 3.2

(i) Define the term inheritance.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

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Fig. 3.3 shows a pedigree diagram of a population of cheetahs.

1 2

3 4 5 6 7 8 9 10

BD BD

11 12 13 14 15 16 17 18 19
bob ?

Key:

female king cheetah female cheetah with spots

male king cheetah male cheetah with spots

Fig. 3.3

(ii) Deduce the genotype of cheetah 11.

..................................................................................................................................... [1]

(iii) Predict the probability of cheetah 14 being a king cheetah.

..................................................................................................................................... [1]

(iv) Describe how a breeder could determine the genotype of cheetah 17.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

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14

(v) When the king cheetah was first discovered it was thought that it was a new species.

Pedigree diagrams of cheetahs proved it was not a new species.

Suggest one type of evidence, other than pedigree diagrams, that can be used to
determine how closely related organisms are.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

(c) Cheetahs are at risk of becoming endangered.

(i) Suggest why the cheetah is at risk of becoming endangered.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

(ii) Describe how species like the cheetah can be conserved.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

[Total: 14]

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18

5 The Galápagos Islands are a group of small islands in the Pacific Ocean.

In 1839 Charles Darwin published a book that described differences in a family of birds called
finches.

Each species of Galápagos finch had:

• a different diet
• a different beak shape, as shown in Fig. 5.1.

Geospiza conirostris Geospiza scandens

Geospiza magnirostris Geospiza fortis

Fig. 5.1

(a) State the genus name for the Galápagos finches shown in Fig. 5.1.
Geospiza
............................................................................................................................................. [1]

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(b) Galápagos finches share a common ancestor.

Suggest how Galápagos finches have evolved different shaped beaks.

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [5]

[Total: 6]

1. Variation
2. Due to mutation ( definition)...producing new allele
3. Selection pressure ( mention)
4. Those who have favorable characteristic ( mention) ...are able to survive
5. Those with less favorable characteristics ( mention) less chance to
survive / die
6. Survival of fittest ...so they breed and pass on the advantageous allele to
the coming generation
7. Increasing the frequency of allele in the population .
8. By natural selection

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Recommended 5

2 The classification of giant pandas, Ailuropoda melanoleuca, is debated by many scientists.

Fig. 2.1 shows a giant panda eating bamboo plants.

Fig. 2.1

Fig. 2.2 shows a red panda, Ailurus fulgens, and a polar bear, Ursus maritimus.

red panda eating bamboo plants polar bear eating fish

Fig. 2.2

(a) State one dietary component that is more likely to be found in bamboo plants than in fish.

............................................................................................................................................. [1]

(b) (i) State two features, visible in Fig. 2.1 and Fig. 2.2, that identify the three animals as all
belonging to the same vertebrate group.

1 ........................................................................................................................................

2 ........................................................................................................................................
[2]

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(ii) DNA can also be used to classify species.

Molecular biologists compared the DNA base sequences of eight species from the same
vertebrate group. They used the differences to draw a classification diagram.

Fig. 2.3 shows the classification diagram for these eight species. The shorter the
horizontal distance from two species to the branching point that they share, the more
similar their DNA sequences are and the more closely the two species are related.

The scale on Fig. 2.3 shows the time at which the molecular biologists estimate that
each branching point occurred.

red panda

:
ferret

giant panda

polar bear

wolf

tiger

human

mouse

100 80 60 40 20 0
million years ago

Fig. 2.3

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External features 7
*
Morphology can also be used to classify species. Some scientists think that morphology
suggests that the giant panda is more closely related to the red panda than it is to the
polar bear.

Discuss the evidence for and against the giant panda being more closely related to
the red panda than it is to the polar bear. Use the information in Fig. 2.1, Fig. 2.2 and
Fig. 2.3 in your answer.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [5]

(iii) State one other type of evidence that is used to classify species.

..................................................................................................................................... [1]

[Total: 9]

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10

3 A researcher investigated genetic variation in fruit flies, Drosophila melanogaster.

The bodies of fruit flies can be black or yellow. A yellow body colour is a recessive feature in fruit
flies.

(a) Two heterozygous fruit flies with black bodies were bred together.

Predict the phenotypes of the offspring and the phenotypic ratio for this cross.

............................................................................................................................................. [1]

(b) In another fruit fly breeding experiment, researchers counted 124 offspring with black bodies
and 121 offspring with yellow bodies.

Draw a genetic diagram to explain the results of this cross. Use the letter B to represent the
allele for black body colour and the letter b to represent the allele for yellow body colour.

parental phenotypes .................................. × ..................................

parental genotypes .................................. × ..................................

gametes , × ,
............. ............. ............. .............

offspring genotypes ..................................................................................................................

expected offspring phenotype ratio ...................... black : ...................... yellow

actual offspring phenotype ratio 124 black : 121 yellow

[5]

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(c) The crab, Cerberusa caeca, lives in dark caves and has no coloured pigment.

Fig. 3.1 is a photograph of C. caeca.

Fig. 3.1

(i) C. caeca and D. melanogaster are both arthropods.

State one feature present in all arthropods but not present in vertebrates.

..................................................................................................................................... [1]

(ii) C. caeca is a crustacean and D. melanogaster is an insect.

State one morphological feature of C. caeca that distinguishes it as a crustacean and

not as an insect.

..................................................................................................................................... [1]

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(d) The ancestors of C. caeca had pigmented bodies.

The lack of a coloured pigment in C. caeca is called albinism and was caused by a mutation
many thousands of years ago.

(i) Explain the mechanism that has resulted in the allele for albinism becoming common in
recent generations in populations of C. caeca.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

(ii) State two factors that can cause mutations.

1 ........................................................................................................................................

2 ........................................................................................................................................
[2]

[Total: 13]

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6

2 (a) Two tomato plants that produce red fruit were bred together.

This cross produced 71 offspring plants with red fruit and 26 offspring plants with yellow fruit.

Complete the genetic diagram to show this cross.

Select a suitable letter to represent the alleles and decide which allele will need a capital
letter and which allele will need a lower case letter.

letter representing the allele for red fruit ...................................................................................

letter representing the allele for yellow fruit ..............................................................................

parental phenotypes red fruit × red fruit

parental genotypes .................................. × ..................................

gametes , × ,
............. ............. ............. .............

offspring genotypes RR, Rr, rr

........................................................................................................

expected phenotype ratio 3

...................... 1
red fruit : ...................... yellow fruit

actual phenotype ratio 71 red fruit : 26 yellow fruit

[6]

(b) Researchers carried out some experiments on tomato plants that were homozygous for fruit
colour.

State how the researchers could be sure that the fruit came from homozygous plants.

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [1]

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(c) The researchers analysed two pigments, chlorophyll and lycopene, in homozygous red
tomato fruit and homozygous yellow tomato fruit. Chlorophyll is found in unripe tomato fruit.

(i) Describe the function of chlorophyll.

...........................................................................................................................................
Direct
...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(ii) State the name of one mineral required for the synthesis of chlorophyll.

..................................................................................................................................... [1]

(iii) The researchers analysed the concentration of the pigments in tomato fruits:
• before they were ready to eat (unripe)
• when they were ready to eat (ripe).

The results of the analysis are shown in Table 2.1.

Table 2.1

chlorophyll concentration lycopene concentration

/ mg per g of tomato fruit / mg per g of tomato fruit
unripe red fruit 10.0 0.0
ripe red fruit 1.2 105.7
unripe yellow fruit 6.2 0.0
ripe yellow fruit 0.4 0.7

Use the information in Table 2.1 to compare the changes in pigments in red fruit and
yellow fruit as they ripen.

...........................................................................................................................................

...........................................................................................................................................
Skills
...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [3]

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(d) A gene is responsible for the production of lycopene in fruits. Geneticists have recently
produced genetically modified pink pineapples using the gene associated with the production
of lycopene.

(i) Genes are found at specific locations on an important biological molecule.

State the name of this biological molecule.

DNA
..................................................................................................................................... [1]

(ii) Describe the disadvantages of genetically modifying crops.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

[Total: 16]

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6

2 (a) A scientist investigated sexual reproduction in flowering plants.

Fig. 2.1 shows the procedure for crossing two plants of the same species.

paint brush used

anthers are removed to pick up pollen
from flower 1 from flower 2

pollen transferred
stigma ready to to the stigma of
receive pollen flower 1

bag placed
around flower 1
and tied tightly

seeds develop in flower 1

after fertilisation

Fig. 2.1

The scientist collected the seeds and germinated them. The leaves and flowers of the offspring
plants showed phenotypic variation as they were not all identical to the parent plants.

The scientist then investigated the chromosomes of all the offspring plants and found that
they had exactly the same number of chromosomes as the parent plants.

(i) Define the term chromosome.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

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(ii) Suggest why the scientist placed a bag around flower 1.

Prevent pollination
...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

(iii) Explain how sexual reproduction results in the variation that the scientist discovered in
Direct the offspring plants.
-

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(iv) The chromosome number of the offspring plants is the same as the chromosome number
of the parent plants in this investigation.

Explain how the chromosome number is maintained from one generation to the next.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

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8
Co dominance
(b) The plant Camellia japonica has flowers that can be white, red or a mixture of these two
colours. When red-flowered plants are crossed with white-flowered plants, all the offspring
plants have flowers with petals that are a mixture of red and white, as shown in Fig. 2.2.

June 2016

Fig. 2.2

• The gene for petal colour in C. japonica is given the symbol P.

• The allele for white petals is given the symbol PW. propw.
• The allele for red petals is given the symbol PR. pRpR
(i) Table 2.1 shows the phenotypes of three different pairs of parent plants.

Complete Table 2.1 by giving all the possible genotypes of the offspring plants that could
be produced by these parent plants.

Space for working.

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Table 2.1

phenotype of female all the possible genotypes of offspring

phenotype of male parent
parent plants produced by this cross

red petals red petals

PR

white petals red petals

petals that are both red petals that are both red
and white and white

[3]

(ii) State the type of inheritance that is shown by petal colour in C. japonica.

..................................................................................................................................... [1]

[Total: 11]

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16

6 Many crop plants are grown as monocultures.

Fig. 6.1 shows the destruction of a monoculture of maize as a result of drought.

Fig. 6.1

(a) Describe the negative impacts to an ecosystem of large-scale monocultures, such as the one
shown in Fig. 6.1.

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

............................................................................................................................................. [3]

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(b) The fruits of maize are produced on structures called cobs. Each cob has many fruits.

Fig. 6.2 shows how the maize cobs have changed over thousands of years as a result of
selective breeding.

fruit

length of
maize cob maize cob

time

Fig. 6.2

State two desirable features, visible in Fig. 6.2, that have been selected from the more
ancient varieties of maize.

1 ................................................................................................................................................

2 ................................................................................................................................................
[2]

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(c) The process of selective breeding involves a series of steps, as shown in Fig. 6.3.

Step 1 select two plants with desirable features

Step 2 transfer pollen from the flower of one plant to a

flower on the second plant

Step 3 use bags to cover the flowers that are pollinated

Step 4 collect the seeds, germinate them and wait for

the plants to grow

Step 5 select the plants from step 4 that have the

desirable features

Step 6 continue step 2 to step 5 for many generations

Fig. 6.3

(i) Explain why the flowers are covered with bags in step 3.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

(ii) Explain why the seeds in step 4 need oxygen to germinate.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]
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(iii) Explain why some of the plants in step 5 may show features not visible in the parent
plants.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

(iv) Suggest why selective breeding should continue for many generations (step 6).

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(v) State how new features, which did not exist in ancient varieties of a crop plant, could
appear.

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [1]

[Total: 12]

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May june 2022 p41 q 3 e

12

(e) If CFTR proteins do not move chloride ions, the liquid in the pancreatic duct becomes very
sticky and the duct can become blocked.

Blocked pancreatic ducts are one effect of cystic fibrosis, which is an inherited disease. Cystic
fibrosis is caused by a mutation of the gene that codes for the CFTR protein.

Fig. 3.3 shows the pedigree diagram of a family that has two people who have cystic fibrosis.

1 2 3

4 5 6 7
Key:

female without cystic fibrosis

male without cystic fibrosis

female with cystic fibrosis

male with cystic fibrosis

Fig. 3.3

(i) The allele that causes cystic fibrosis is a recessive allele.

Describe and explain the evidence shown in Fig. 3.3 that cystic fibrosis is caused by a
Skills recessive allele.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

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13

(ii) Person 7 is expecting a child with a man who is heterozygous for cystic fibrosis.

Complete the genetic diagram to predict the probability of person 7 and the heterozygous
man having a child with cystic fibrosis.

Use the symbol A for the dominant allele and a for the recessive allele.

parental genotypes aa
................ ................

gametes +

Direct

genotypes of offspring .......................................................................................................

phenotypes of offspring .....................................................................................................

probability of having a child with cystic fibrosis .................................................................

[5]

[Total: 21]

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