GENETICS PROBLEMS

GENETICS PROBLEMS - Incomplete Dominance

BIOL 1406

Gene information for first two problems: In a certain stain of chickens, feather color is determined by a pair of alleles that show incomplete dominance. The two alleles are F^b and F^w. A chicken that is black has the genotype F^b and F^b. A chicken that is white has the genotype F^w F^w and a chicken that is heterozygous (F^b F^w) would have blue feathers.

1. If a black feathered chicken is cross with a white feathered chicken, what color would the offspring be?

Black Chicken = F^bF^b

White Chicken = F^wF^w

Offspring = all blue chickens (F^bF^w)

2. If two blue feathered chickens were crossed, what is the expected phenotype ratio of their offspring?

Blue (FbFw) X Blue (FbFw)

	F^b	F^w
F^b	F^bF^b	F^bF^w
F^w	F^bF^w	F^wF^w

1 Black Chicken

2 Blue Chickens

1 White Chicken

Gene information for next problems: Crosses between red (C^rC^r) and white (C^wC^w) shorthorn cattle result in roan (C^rC^w) offspring. This is an example of incomplete inheritance. The presence or absence of horns is a separate gene with regular dominant and recessive alleles. Polled (hornless) cattle show the dominant trait (H) and horned cattle have the recessive trait (h).

3. A bull is homozygous polled and is red in color. He is mated with a horned, roan cow. What are the expected phenotypes in their offspring and the percentage chance for each?

Homozygous polled, Red Bull = HHC^rC^r

Horned, Roan Cow = hhC^rC^w

	hC^r	hC^w
HC^r	HhC^rC^r	HhC^rC^w

50% Horned, Red

50% Horned, Roan

4. A roan bull that is heterozygous polled is mated with a white heterozygous polled cow. What would be the expected phenotypes of their offspring and what is the expected chance of each?

Heterozygous polled, Roan Bull = HhC^rC^w

Heterozygous polled, White Cow = HhC^wC^w

	HC^w	hC^w
HC^r	HHC^rC^w	HhC^rC^w
HC^w	HHC^wC^w	HhC^wC^w
hC^r	HhC^rC^w	hhC^rC^w
hC^w	HhC^wC^w	hhC^wC^w

Polled, Roan = 3 = 37.5%

Polled, White = 3 = 37.5%

Horned, Roan = 1 = 12.5%

Horned, White = 1 = 12.5%

Gene information for next problems: In snapdragons, the alleles for flower color show incomplete dominance. C^RC^R produces red flowers; C^WC^W produces white flowers and C^RC^W produces pink flowers. The height of the plant is determined by a separate gene with regular dominant and recessive alleles. Normal height (D) is dominant over dwarf height (d).

5. A snapdragon that is heterozygous normal in height and has white flowers is crossed with a plant that is dwarf in height and has red flowers. What is the expected phenotype ratio in the offspring?

(Dd C^WC^W) X (dd C^RC^R)

DC^W, DC^W, dC^W, dC^W dC^R, dC^R, dC^R, dC^R

	dC^R	dC^R
DC^W	DdC^RC^W	DdC^RC^W
dC^W	ddC^RC^W	ddC^RC^W

Expected Phenotype Ratio:

1 Tall with Pink : 1 Dwarf wtih Pink

6. A plant that is homozygous normal in height and has ping flowers is crossed with a dwarf plant that has pink flowers. What is the expected phenotype ratio in the offspring?

(DDC^RC^W) X (ddC^RC^W)

DC^R, DC^W, DC^R, DC^W dC^R, dC^W, dC^R, dC^W

	dC^R	dC^W
DC^R	DdC^RC^R	DdC^RC^W
DC^W	DdC^RC^W	DdC^WC^W

Expected Phenotype Ratio:

Tall with Red = 1

Tall with Pink = 2

Tall with White = 1