Work sheet (1)

1. In Mendel's pea plants, tall (T) is dominant to short (t). A heterozygous tall plant (Tt) is
crossed with a homozygous short plant (tt). What are the expected phenotypes of the
offspring?

A. All tall C. 75% tall, 25% short

B. All short D. 50% tall, 50% short

2. Cystic fibrosis is a recessive genetic disorder. If two carriers (Cc) have a child, what is the
probability that the child will have cystic fibrosis (cc)?

A. 0% C. 50%
B. 25% D. 75%

3. In fruit flies, red eyes (R) are dominant to white eyes (r). A red-eyed fly (RR) is crossed
with a white-eyed fly (rr). What is the genotype of the F1 generation?

A. RR C. Rr
B. Rr D. Rr and rr

4. Snapdragons exhibit incomplete dominance for flower color. Red (R) and white (r) alleles
produce pink (Rr) flowers. If two pink-flowered snapdragons (Rr) are crossed, what is the
expected phenotypic ratio of the offspring?

A. 3 red : 1 white C. 1 red : 1 white

B. 1 red : 2 pink : 1 white D. All pink

5. In mice, agouti coat color (A) is dominant to black (a). If a heterozygous agouti mouse (Aa)
is crossed with a black mouse (aa), what is the probability that the offspring will have a
black coat?

A. 25% C. 75%
B. 50% D. 100%

6. A plant breeder crosses two pea plants. One has yellow seeds (YY) and the other has green
seeds (yy). Assuming yellow is dominant, what will be the genotype of all the F1 offspring?
A. YY C. Yy
B. Yy D. Some YY, some Yy

7. trait is inherited through a monohybrid cross and the F2 generation shows a 3:1
phenotypic ratio, what does this indicate about the alleles involved?
A. Both alleles are dominant.
B. Both alleles are recessive
C. One allele is dominant and the other is recessive

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D. The alleles show incomplete dominance

8. What is the difference between phenotype and genotype; homozygous and heterozygous
individuals, monohybrid and dihybrid, test cross, (discuss in groups and present it to the
class).

9 . Show F1, F2, homozygous, heterozygous, dominant, recessive, genotype, phenotype

using the Punnett square for pea plants with:

A. Round ( RR) versus wrinkled ( rr) seed shapes,

B. Pure yellow seed versus pure green seed

Phenotype vs. Genotype

 Genotype: This is the genetic makeup of an organism. It refers to the specific alleles
(versions of a gene) an individual carries. Think of it as the recipe or blueprint for a trait.
o Example: A pea plant's genotype for seed color could be YY (two yellow
alleles), Yy (one yellow and one green allele), or yy (two green alleles).
 Phenotype: This is the observable physical characteristic of an organism. It's how the
trait appears outwardly.
o Example: A pea plant with YY or Yy genotype will have a yellow seed
phenotype, while a yy genotype will result in a green seed phenotype.

Homozygous vs. Heterozygous

 Homozygous: An individual is homozygous at a specific gene if it carries two identical
alleles for that gene. Example: YY (homozygous dominant) or yy (homozygous
recessive)
 Heterozygous: An individual is heterozygous at a specific gene if it carries two different
alleles for that gene. Example: Yy (one dominant yellow allele and one recessive green
allele)
Monohybrid vs. Dihybrid
 Monohybrid: A monohybrid cross involves one trait or gene being studied.
Example: Crossing a pea plant with yellow seeds (YY) with a pea plant with green
seeds (yy) is a monohybrid cross.
 Dihybrid: A dihybrid cross involves two traits or genes being studied
simultaneously. You're looking at how different alleles of two different genes are
inherited.
 Crossing a pea plant with yellow, round seeds (YYRR) with a pea plant with green,
wrinkled seeds (yyrr) is a dihybrid cross.
Test Cross
 A test cross is a procedure used to determine the genotype of an individual
displaying a dominant phenotype when the genotype is unknown.
 The individual with the dominant phenotype (but unknown genotype – could be
homozygous dominant or heterozygous) is crossed with an individual known to be
homozygous recessive for the trait in question
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8. In Mendel's pea plants, tall (T) is dominant to short (t), and round seeds (R) are dominant
to wrinkled seeds (r). A plant heterozygous for both traits (TtRr) is crossed with another
plant heterozygous for both traits (TtRr). What is the expected phenotypic ratio of the
offspring?
A. 9 tall, round: 3 tall, wrinkled: 3 short, round: 1 short, wrinkled
B. 3 tall, round: 1 short, wrinkled
C. 1 d) All tall, round
D. All black, curly
9. In dogs, black fur (B) is dominant to brown fur (b), and curly fur (C) is dominant to straight fur
(c). A dog heterozygous for both traits (BbCc) is crossed with a dog with brown fur and straight
fur (bbcc). What is the expected phenotypic ratio of the offspring?
A. 9 black, curly: 3 black, straight: 3 brown, curly: 1 brown, straight
B. 1 black, curly: 1 black, straight: 1 brown, curly: 1 brown, straight

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C. 3 black, curly: 1 brown, straight
D. All black, curly
10. In fruit flies, red eyes (R) are dominant to white eyes (r), and long wings (L) are dominant to
vestigial wings (l). A red-eyed, long-winged fly (RRLl) is crossed with a white-eyed, vestigial-
winged fly (rrll). What are the possible genotypes of the offspring?

A. RrLl only C. RRLL, RrLl, rrLl, rrll

B. RrLl and rrll D. RrLl, Rrll, rrLl, rrll

11. A plant with purple flowers (P) and smooth seeds (S) is crossed with a plant with white flowers (p)
and wrinkled seeds (s). The F1 generation all have purple flowers and smooth seeds (PpSs). If the
F1 plants are allowed to self-pollinate, what is the probability of obtaining an F2 plant with white
flowers and wrinkled seeds (ppss)?

A. 1/16 C. 1/2
B. 1/4 D. 9/16

12. . In guinea pigs, black fur (B) is dominant to white fur (b), and rough coat (R) is dominant to
smooth coat (r). Two guinea pigs are crossed: one is black and rough (BBRR), and the other is
white and smooth (bbrr). What will be the genotype of all the F1 offspring?

A. BBRR C. bbrr
B. BbRr D. Bbrr

13. If two parents are heterozygous for two traits (AaBb), how many different genotypes are
possible in their offspring?

A. 2 C. 8
B. 4 D. 9

14. What is the phenotypic ratio typically observed in the F2 generation of a dihybrid cross
when both parents are heterozygous for both traits, and the traits follow complete
dominance?

A. 9:3:3:1 C. 1:1:1:1
B. 3:1 D. 1:2:1

Answers:

1. a) 9 tall, round: 3 tall, wrinkled: 3 short

2. b) 1 black, curly: 1 black, straight: 1 brown, curly: 1 brown, straight
3. b) RrLl and rrll
4. a) 1/16
5. b) BbRr
6. d) 9
7. a) 9:3:3:1

E.
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