MODIFICATIONS TO BIO 170|

MENDEL’S CLASSIC RATIOS GENETICS

WHAT COLOR OFFSPRING WOULD YOU GET WHEN YOU CROSS A PURE
(HOMOZYGOUS) RED SNAPDRAGON WITH A PURE WHITE SNAPDRAGON?

?
2
ODDLY ENOUGH, NEITHER RED NOR WHITE

Snapdragon Flower
Color is controlled by
Incomplete Dominance
and a new 3rd
phenotype is seen.

3
HOW DOES INCOMPLETE DOMINANCE WORK?
INCOMPLETE DOMINANCE IS A BLENDING
Like Paint, the RED
Pigment “MIXES”
with the WHITE to
create PINK-
FLOWERED
offspring

5
INCOMPLETE DOMINANCE CAN BE SEEN IN:

Horses ( Chestnut x Cremello

→ Palomino)

Snapdragons

Japanese Four O’ Clocks

Many flowers exhibit

incomplete dominance
6
ALLELE NOTATION
HOW DO YOU WRITE OUT
THE GENOTYPE WHEN
BOTH ALLELES ARE
DOMINANT?

7
YOU MUST USE DIFFERENT LETTERS

Choose different letters to represent each form

(In this case we’ll use “W” for the white allele
and “R” for the Red allele).

Remember to always use CAPITAL letters. This is

incomplete DOMINANCE.
8
SO…THE CROSS BETWEEN PURE SNAPDRAGONS LOOKS LIKE THIS

R R

W RW RW

W RW RW

9
YOU’VE SEEN A CROSS BETWEEN PURE SNAPDRAGONS, NOW DO THE PUNNET
SQUARE FOR A CROSS BETWEEN TWO HYBRIDS (HETEROZYGOTES).

What are the alleles of a heterozygous snapdragon?

• RW

What is the genotypic ratio?

• 1 RR : 2 RW : 1 WW

What is the phenotypic ratio?

• 1 Red : 2 Pink : 1 White
10
WHAT KIND OF GENETICS DO THESE ORGANISMS EXHIBIT?

11
 A cross between 2 tabbies (the
CODOMINANCE heterozygotes) results in
1 black : 2 tabbies : 1 tan cat
black-cat

The same ratios as Incomplete

1178198189563

Dominance occur:
A ratio of 1:2:1 for both
genotype and phenotypes of
a monohybrid cross
→ 5561b6d64ca720aa71b5945c6ebb4d16-grande
tan%2520cat%2520002

Different Phenotype:
The two original phenotypes
are combined to give a
SPOTTED or MULTICOLORED
phenotype. 12
NOTATION FOR CODOMINANCE
1. Choose a letter to represent the gene.
2. Choose different letters to represent each of
the alleles.
3. Take the letters representing the alleles and
turn them into superscripts.
4. Combine the two. Remember to use capital
letters.
13
 WRITING OUT THE GENOTYPE
1. We’re going to use C to represent Coat Color of a shorthorn
cow.
2. Roan coat color is a combination of Red and White hair so
we’ll use “R” to represent Red and “W” to represent white.
3. R → R and W → W
4. C + R → CR and C + W → CW
5. So a Red Cow would be CRCR , a white cow would be CWCW,
and a roan cow would be CRCW
14
CODOMINANCE OCCURS IN:

Shorthorn Cow (White + Red)

Blue Roosters (White + Black)

Human Blood Typing (AB)

Tabby Cats (Black and Tan Fur)

15
LET’S PRACTICE
Tabby cats exhibit codominance between tan and black fur.
1. Can Tan Cat be heterozygous? Why or Why not?
2. If you mate a tabby with a black cat, what is the phenotypic ratio
of their offspring?
3. If the offspring of two cats are composed of 36 tabbies and 40
black cats, what are the parental phenotypes and genotypes?

16
NEXT: ABO BLOODTYPING

17
BLOOD TYPING

Human blood typing is an example

of both CODOMINANCE and
MULTIPLE ALLELES

What does Multiple Alleles Mean?

18
THE ALLELES
A and B blood types are coded for by the alleles:
IA and IB respectively. These two alleles are
CODOMINANT.

Blood type O is coded for by the allele i and is

recessive to both IA and IB (notice the lower case letter).

I designation stands for isoagglutinogen, another term

for antigen
19
ALLELES AND THEIR BLOOD TYPES

20
21
 LET’S PRACTICE
Could a man with AB blood have an AB child with a woman with
type O blood?

If a child has type B blood, what are all the possible blood types
for his/her parents?

A paternity test is being performed. The child has type A blood.

The mother is type A. Potential Dad #1 has type B blood.
Potential Dad #2 has type O blood. Who is the father?

Challenge: What two parents could produce the most diverse

children as far as blood type is concerned?

22
PUNNETT SQUARE – BLOOD GROUPS:
Show a cross between a person who has heterozygous A type
blood & a person who has homozygous B type blood.
IAi x IBIB

Genotypes:

Phenotypes:

23
MULTIPLE ALLELES

Bombay Phenotype

Due to a rare recessive mutation h,

at a locus separate from that
controlling the A and B antigens

Woman in bombay (hh phenotype)

• Blood type O
• Parents (one is AB)
• Children (type B)
24
Rh COMPATIBILITY
Landsteiner (blood typing pioneer)

Antisera against monkey (Rhesus macacca)

Rh-factor
• Rh+ = RR or Rr
• Rh- = rr
Rh- mother and Rh+ father

Erythroblastosis fetalis
• Serious anemia or breakdown of RBC among newly born fetuses
25
Rh COMPATIBILITY

An Rh negative person is born without the antigen and does not form
antibodies unless he or she is specifically sensitized to it.

Sensitization can occur with RBC transfusions from an Rh positive person

or exposure during pregnancy and birth.

An Rh positive person can receive an RBC transfusion from an Rh

negative donor.

Rh negative people MUST NEVER receive Rh positive blood.

26
27
Rh COMPATIBILITY

28
 LET’S PRACTICE
Suppose a newborn baby was
accidentally mixed up in the hospital.
In an effort to determine the parents
of the baby, the blood types of the
baby and two sets of parents were
determined. Baby 1 had type O Mrs.
Brown had type B Mr. Brown had
type AB. Mrs. Smith had type B Mr.
Smith had type B
• a. Draw Punnett squares for each couple
• b. To which parents does baby #1 belong?
Why?
29
 MORE PRACTICE
In the 1950’s, a young woman sued
film star/director Charlie Chaplin for
parental support of her illegitimate
child. Charlie Chaplin’s blood type
was already on record as type AB.
The mother of the child had type A
and her son had type O blood.
• a. Complete a Punnett square for the possible
cross of Charlie and the mother.
• b. The judge ruled in favor of the mother and
ordered Charlie Chaplin to pay child support
costs of the child. Was the judge correct in his
decision based on blood typing evidence?
Explain why or why not.
30
 NEXT..LETHAL ALLELES

31
https://www.pinterest.ph/pin/292522938286671169/
 PREVENTION
It is important to immunize Rh-
negative mothers after their first
pregnancy to guard against future Rh
incompatibility reactions.

Immediately after childbirth, anti-Rh

antibody (RhoGAM) is injected in the
mother (also known as antibody D).

Immunization must be repeated after

each pregnancy, including ectopic
pregnancies and miscarriages.
32
MULTIPLE ALLELES:
DUCK FEATHER PATTERNS
Three alleles determine the type of
plumage in mallard ducks:

MR (Restricted) > M (Mallard) > md

(Dusky)

33
 LET’S PRACTICE
MR (Restricted) > M (Mallard) > md (Dusky)

The ducks in the following lists are crossed to

produce the offspring shown. Give the
genotypes of the parent and offspring in each
cross:
A. restricted x dusky
Progeny : ½ mallard ; ½ restricted
B. restricted x mallard
Progeny : ½ restricted; ¼ mallard; ¼ dusky
C. mallard x dusky
Progeny : 100% mallard
34
https://www.thespruce.com/pictures-of-mallards-4121965
MULTIPLE ALLELES:
COAT COLOUR IN RABBITS
Four phenotypes and four alleles:

Allelic series is C > cch > ch > c (which is most

dominant)

Coat Color Phenotype Genotype

Full Color CC, Ccch, Cch, Cc
Chinchilla cchcch, cchch, cchc
Himalayan chch, chc
Albino cc
35
LET'S PRACTICE
What types of offspring could be produced by a full color rabbit that had a
genotype of C cch that was bred with a Himalayan rabbit that was ch c?

36
MORE PRACTICE Allelic series is C > cch > ch > c (which is most dominant)

Predict the phenotype for a rabbit with a c h cch

genotype.

Predict the phenotype for a rabbit with a Cch genotype.

Would it be possible to obtain white rabbits if one

parent is white and the other is chinchilla?

Would it be possible to obtain chinchilla rabbits if one

parent is Himalayan and the other is white?

A chinchilla rabbit is mated with a Himalayan. Some

offspring are white. What are the parents’ genotypes
37
NOW SOLVE THIS

38
LETHAL GENES:

Some genes are lethal when

present in the homozygous https://evolutionaryedges.weebly.com/achondroplasia/archives/04-2017

condition (dominant or
recessive)
• Achondroplasia, cystic fibrosis, sickle-
cell anemia (recessive lethal)
• Huntington’s disease (dominant lethal) https://www.britannica.com/science/sickle-cell-anemia

39
"CREEPER" ALLELE IN CHICKENS
• Chicks
In chickens, when an embryo
heterozygous for
contains two copies of the
dominant gene known as
creeper, the embryo dies
inside the eggshell.
the gene survive.

40
MANX CATS

Show the cross

between a manx cat
and a normal cat.

41
42
 A • Agouti (wild type allele)

MOUSE COAT COLOR AY • Yellow (mutant allele)

43
EXAMPLE WITH MOUSE COAT COLOUR
Yellow is dominant to grey
Cross hybrid yellow mice Yy x Yy

Resulting offspring:
2 yellow to 1 grey
One genotype is missing

Somehow the YY genotype is lethal

The 2:1 ratio is the typical ratio for a lethal gene.
44
 ANSWERS TO SAMPLES:

A •child’s phenotype is O, the genotype must be ii

(recessive)
•father (A) and mother (B) must both carry the
recessive allele
B •Father’s genotype IAi and mother’s genotype IBi

C Chance of having
an AB type baby is
25%
45
a) The offspring occur in three types, classified as long, round and oval
(intermediate), suggesting incomplete dominance
• Long (L) Round (L’) Oval (LL’) - heterozygous

Test this idea…. LL’ x LL’ Gives a ratio of 1 long to 2 oval to 1

round radishes.
b) (LL x LL), all the offspring will be
long.
c) (L’L’ x L’L’), all the offspring will be
round.

46
A) Since ¼ of the eggs don’t hatch – lethal gene
Crested (C) and non-crested (c) then both parents would have to be
Cc ( eg. Cc x Cc)
All the eggs with CC genotype would
not hatch
Viable offspring would hatch in a ratio
of 2 crested to 1 non-crested

B) Cc x cc

Ratio: 1Cc to 1 cc
1 crested to 1 non 47
A)
Bull’s genotype RR, Cow’s genotype R’R’
B)
RR’ x R’R’

All of the offspring have RR’

genotype and will be roan Ratio of 2 roan to 2 white calves 48
BIO 170 | GENETICS
JT IMPERIAL
SEX DETERMINATION & SEX-LINKED
TRAITS
50
Red-green colourblindness

Hemophilia

Duchenne muscular
dystrophy

51
WHAT IS THE DIFFERENCE BETWEEN AN AUTOSOME AND A SEX-
CHROMOSOME?

Autosomes are the first 22

homologous pairs of human
chromosomes that do not influence
the sex of an individual.

Sex Chromosomes are the 23rd

pair of chromosomes that
determine the sex of an individual

52
SEX CHROMOSOMES:

Which is male?… female?

What is the genotype of each sex?
Which parent determines the sex of the offspring?
53
 HOMOZYGOUS VS HEMIZYGOUS

https://ib.bioninja.com.au/standard-level/topic-3-genetics/34-inheritance/types-of-zygosity.html

https://www.differencebetween.com/difference-between-homozygous-and-hemizygous/

54
 • one of the two X chromosomes present in
females is inactivated
X - INACTIVATION • ensures that females do not produce twice as
many X-linked gene proteins as males who
possess one X chromosome) who possess one X
chromosome)

55
SEX DETERMINATION:
How many chromosomes do humans have?

How many of these are “sex” chromosomes?

Which parent determines the sex of an offspring?

Are there any traits/conditions that are more common in

one sex than the other?
56
Sex linked • The gene (pair) that determines a
character (e.g. hemophilia) is
trait located on the sex chromosomes

X-linked • A sex-linked trait is where the

gene or allele for the trait is found
trait on the X chromosome

Y-linked • A sex-linked trait where the gene

or allele for the trait is found on
trait the Y- chromosome
57
SEX-LINKED TRAITS

Traits (genes) located on the sex chromosomes

Sex chromosomes are X and Y

XX genotype for females

XY genotype for males

Many sex-linked traits carried on X chromosome

58
SEX-LINKED TRAITS
Example: Eye color in fruit flies
Sex Chromosomes

fruit fly
eye color

XX chromosome - female Xy chromosome - male

59
SEX-LINKED TRAIT PROBLEM
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY x XrXr

Remember: the Y chromosome in males does not

carry traits. Xr Xr
RR = red eyed
Rr = red eyed XR
rr = white eyed
XY = male Y
XX = female 60
SEX-LINKED TRAIT PROBLEM
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY x XrXr

Remember: the Y chromosome in males does not

carry traits. Xr Xr
RR = red eyed
Rr = red eyed XR
rr = white eyed
XY = male Y
XX = female
61
SEX-LINKED TRAIT SOLUTION:

Xr Xr
50% red eyed
XR XR Xr XR Xr
female
50% white eyed
Y Xr Y Xr Y male

62
FEMALE CARRIERS

63
QUESTION: IS IT POSSIBLE FOR A FEMALE CARRIER
OF HEMOPHILIA TO HAVE A DAUGHTER WITH
HEMOPHILIA?

XH Xh
Xh XH Xh XhXh

Y XH Y Xh Y

64
Color blindness
• An X-linked recessive trait where a affected individual could not
distinguish red from green color (red green color blindness)
Hemophilia
• An X-linked recessive trait where an affected individual suffers
from delayed blood clotting during injuries because of the
absence of certain blood clotting factors
Hypertrichosis pinnae auris
• A Y-linked trait where affected males have hair growing from
their external ears
65
 X-LINKED RECESSIVE DISORDERS

https://www.tumblr.com/intelligentliving/189094834117/x-linked-recessive-inheritance
66
https://healthjade.net/duchenne-muscular-dystrophy/#google_vignette
X-LINKED RECESSIVE DISORDERS

67
68
COLOURBLINDNESS SELF TEST:
Can you see the hidden numbers?

NUMBERS: 5 | 8 | 9 | 5 | 3 | 5 | 9 | 10 | 69
HIDDEN SHAPES:

SHAPES:
Plate 1 - Circle and arch
Plate 2 - Circle, star and square 70
SEX-LINKED TRAITS:
•Some genes are found on the sex chromosomes
•Some are found on the X sex chromosome but not the Y
Ex – the colour vision gene is on the X chromosome
- NOT FOUND ON THE “Y”

Sex-linked traits are RECESSIVE (mostly) traits

that are found on the ‘x’ sex chromosome
71
A human pedigree of the X-linked color-blindness trait.

The photograph is of an Ishihara color-blindness chart, which tests for red–green color
blindness.

Red–green color-blind individuals see a 3 rather than the 8 visualized by those with normal
color vision.
72
HYPERTRICHOSIS – HUMAN WEREWOLF SYNDROME:
Congenital generalized
hypertrichosis (CGH)
Rare, X-linked dominant trait
Found in a single multigenerational
Mexican family

73
Red-green colorblindness is a recessive sex-linked trait, found on the X chromosome, not the Y.

Males only have one X chromosome, they have a much greater chance of having red-green colorblindness.

Females would have to be homozygous recessive in order to have red-green colorblindness.

74
Calico cat

75
Solve :
A black female cat is mated with an
orange male cat. They produce two
tortoiseshell females, two black males,
one orange female, and one
tortoiseshell male, for a total of six
kittens. What are the genotypes of all
the individuals in this cross.
76
https://www.chegg.com/homework-help/questions-and-answers/x-linked-genetics-calico-cat-calico-coat-color-found-cats-caused-sex-linked-codominant-all-q99260142
HUMAN X-LINKED TRAITS

77
WRITING SEX-LINKED GENOTYPES:

78
MORE PRACTICE:
 In humans the gene from normal blood clotting, H, is
dominate to the gene for hemophilia, h. This is a sex-
linked trait found on the X chromosome. Serena with
normal blood clotting has four children. They are a normal
son, a hemophiliac son, and two normal daughters. The
father, Simon has normal blood clotting. What is the
probable genotype for each member of the family?

79
ANOTHER ONE….
James with normal vision marries Kath who is
a carrier for color blindness. What are the
possible genotypes and phenotypes of their
children.

80
JUST ONE MORE….

A hemophiliac man, Rudy Dots marries

Lenny Robs who is a carrier for the
disease. What are the possible genotypes
and phenotypes of their children? Should
they even consider having children?

81
OTHER SEX-RELATED TRAITS

82
Sex influenced characteristics
•are determined by autosomal
genes and are inherited according
to Mendel’s principles, but they are
expressed differently in males and
females
83
84
PATTERN BALDNESS IS A SEX-INFLUENCED TRAIT

This trait is seen in three generations of the Adams family: a) John Adams, 2nd President of
USA, was father to b) John Quincy Adams, who was father to c) Charles Francis Adams

Pattern baldness reults from an autosomal gene that is thought to be dominant in males
and recessive in females 85
PATTERN BALDNESS

86
Sex- Limited Characteristics
• extreme form of sex-influenced
inheritance, a sex limited
characteristic is encoded by
autosomal genes that are
expressed in only one sex—the trait
has zero penetrance in the other sex
87
 Cock feathering in chickens, an autosomal Mandrills : males exhibit a more vibrant coloration Pheasants : In addition to their larger size, male
recessive trait that is limited to males on their faces and behinds pheasants differ from females in their colorful,
decorative plumage and extra-long tails.

Elephant Seals : These pinnipeds are named for Mandarin Ducks: Males are especially striking
the males' large proboscises (noses) that elongate with their red bills, pronounced crests, and array of
during puberty and wind up looking like stunted Orangutans : At sexual maturity, male orangutans
colorful feathers
elephant trunks. begin to develop enlarged cheek flaps and throat
sacs meant to exhibit their dominance
SEXUAL DIMORPHISM

89
90