SCN3230-ABED_1: Module 6 Lesson 3 - 7

Lesson 3 — Incomplete Dominance, Codominance, and Multiple Alleles

Self-Check

Answer the following questions to check your understanding of the material in this lesson.

In shorthorn cattle, red is codominant with white. The hybrid is called roan. A roan mates with a roan. Use a Punnett Square to determine the expected phenotypes of the offspring.
The alleles for hair type show incomplete dominance. One allele ( c) is for curly hair. Another allele (s) is for straight hair. The hybrid is wavy. A wavy-haired person marries a curly-haired person. Use a Punnett Square to determine the expected phenotypes of their children.
A rooster with grey feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are grey, 6 are black, and 8 are white.
1. What is the simplest explanation for the inheritance of these colours in chickens?
2. What colour offspring can you expect from the mating of a grey rooster and a black hen?

Colour patterns in a species of duck are determined by one gene with three alleles. Alleles H and I are semi-dominant (that is, incomplete dominance), and allele i is recessive to both. How many phenotypes are possible in a flock of ducks that contains all possible combinations of these three alleles?

Note that blood type genotypes may be written using an "I" before the A and B, such as I^AI^A and I^Bi, etc. However, you can use the simpler method without the "I".

Hazel has type B blood (genotype Bi) and Elijah has type O blood (genotype ii). If they have children, what is the chance they will have a type B child? What is the chance they will have a type A child?

A woman with type A blood and a man with type B blood potentially could have offspring with
1. blood type A
2. blood type B
3. blood type AB
4. blood type O
5. all the above

What are the possible blood types of the offspring of a cross between individuals that are type AB and type O?
1. AB or O
2. A, B, or O
3. A or B
4. A, B, AB, or O
5. A, B, or AB

Check your work.

Self-Check Answers

C^R= red, C^W= white, C^RC^W= roan
Parents: C^RC^Wx C^RC^W
Phenotypes of F1= 1 Red : 2 roan : 1 White

	C^R	C^W
C^R	C^RC^R	C^RC^W
C^W	C^RC^W	C^WC^W

H^C= curly, H^S= straight, H^CH^S= wavy
Parents: H^CH^S x H^CH^C
Phenotypes of F1 = 2 wavy : 2 curly

	H^C	H^S
H^C	H^CH^C	H^CH^S
H^C	H^CH^C	H^CH^S

Incomplete dominance due to the three possible phenotypes
C^B= black, C^W = white, C^BC^W= grey

Parent: C^BC^B x C^BC^W
Phenotypes of F1 = 50% grey : 50% black

	C^B	C^B
C^B	C^B C^B	C^B C^B
C^W	C^BC^W	C^BC^W

Four Possible Phenotypes:

D^HD^H, D^HDⁱ= H
D^ID^I, D^IDⁱ = I
D^HD^I = HI
DⁱDⁱ= i

Parents: BO x OO

Phenotypes of F1 = 50% Type B : 50% Type O

There is 0% chance that they will have a child with blood type A.

	B	O
O	BO	OO
O	BO	OO

Possible Genotypes for Type A Blood = I^AI^A or I^Ai

Possible Genotypes for Type B Blood = I^BI^B or I^Bi

Use the genotype that will provide the most variation in the F1 generation.

	I^A	i
I^B	I^AI^B	I^Bi
i	I^Ai	ii

Phenotypes of F1 = 25% Type AB : 25% Type B : 25% Type A : 25% Type O

Possible Genotype for Type AB Blood = I^AI^B

Possible Genotype for Type O Blood = ii

	I^A	I^B
i	I^Ai	I^Bi
i	I^Ai	I^Bi

Phenotypes of F1 = 50% Type A : 50% Type B

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Examination.

Use the following information to answer the next question.

Several geneticists studied M. jalapa plants with deep crimson flowers and M. jalapa plants with yellow flowers. Cross-pollinating these plants produced plants with scarlet-red flowers (F1 generation).

These F1 plants were allowed to self-pollinate, and the resulting seeds produced M. jalapa plants with three different flower colours. Data similar to the following were collected for flower colour:

140 deep crimson

310 scarlet-red

160 yellow

With respect to the alleles for flower colour, these results indicate
1. X-linked inheritance
2. gene-linked inheritance
3. dominant-recessive inheritance
4. incomplete dominance inheritance

If a woman has blood type A and her husband has blood type B, which of the following genotypes would be possible for their child with blood type A?
1. I^Ai
2. I^AI^A
3. I^BI^B
4. I^AI^B

Which of the following rows indicates the relationship between the I^A and I^B alleles and the relationship between the I^A and i alleles for the blood type gene?

Row	Relationship between I^A and I^B	Relationship between I^A and i
A.	codominant	codominant
B.	codominant	dominant-recessive
C.	dominant-recessive	codominant
D.	dominant-recessive	dominant-recessive

Use the following information to answer the next question.

Cat coat colour results from the interaction of three genes. A gene for black-based colours is located on an autosomal chromosome. A gene for red-based colours is located on the X chromosome. A different gene located on a separate autosomal chromosome determines pigment density in cat hair.

The black-based gene has three possible alleles: B - black, b - chocolate, and b¹- cinnamon. If pigmentation in cat hair is dense, the phenotypes listed below are possible.

Genotype	Phenotype
BB, Bb, Bb¹	Black
bb, bb¹	Chocolate
b¹b¹	Cinnamon

According to the data above, the relationship among these alleles is such that the
1. black allele is codominant with the chocolate and cinnamon alleles
2. black allele is codominant with the chocolate allele, and the chocolate allele is codominant with the cinnamon allele
3. black allele is dominant over the chocolate and cinnamon alleles, and the chocolate allele is dominant over the cinnamon allele
4. black allele is dominant over the chocolate and cinnamon alleles, and the chocolate and cinnamon alleles are codominant

Check your work.

Diploma Question Answers

B - codominant; dominant-recessive

C - Black allele is dominant over the chocolate and cinnamon alleles, and the chocolate allele is dominant over the cinnamon allele.