In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette.
a. What is the genotype for black chickens? BB
b. What is the genotype for white chickens? WW
c. What is the genotype for erminette chickens? BW
d. If two erminette chickens were crossed, what is the probability that:
a. They would have a black chick?
b. They would have a white chick?
e. A black chicken and a white chicken are crossed.
f. An erminette chicken and a white chicken are crossed.
g. An erminette chicken and a white chicken are cro
The Correct Answer and Explanation is:
Answers:
a. Genotype for black chickens: BB
b. Genotype for white chickens: WW
c. Genotype for erminette chickens: BW
d. If two erminette (BW) chickens were crossed:
- a. Probability of black chick (BB): 25%
- b. Probability of white chick (WW): 25%
- Probability of erminette chick (BW): 50%
e. If a black chicken (BB) and a white chicken (WW) are crossed:
- All offspring will be BW (erminette). Probability of erminette: 100%
f. If an erminette chicken (BW) and a white chicken (WW) are crossed:
- 50% BW (erminette), 50% WW (white)
g. If an erminette chicken and a white chicken are crossed (again):
- Same as f: 50% BW (erminette), 50% WW (white)
Explanation
In chickens, feather color can be determined by a codominant inheritance pattern. Codominance means that both alleles in a heterozygous genotype are fully and equally expressed. This differs from dominant-recessive inheritance, where only the dominant allele is visible in the phenotype. In this case, the allele for black feathers is B and for white feathers is W. When a chicken inherits both alleles (BW), it does not show one color over the other but instead expresses both traits simultaneously, producing a speckled or erminette appearance.
When two erminette chickens (BW × BW) are crossed, a Punnett square shows the possible combinations:
- BB (25%) – black
- BW (50%) – erminette
- WW (25%) – white
Thus, each chick has a 1 in 4 chance of being black, a 1 in 4 chance of being white, and a 1 in 2 chance of being erminette.
When a black chicken (BB) is crossed with a white chicken (WW), all offspring receive one B and one W allele, making them all BW – 100% erminette.
When an erminette chicken (BW) is crossed with a white chicken (WW), half the offspring inherit W from both parents (WW, white), and the other half inherit B from the erminette and W from the white (BW, erminette). The result is a 50-50 ratio.
This genetic scenario illustrates how codominance allows both alleles to be equally expressed, creating a unique third phenotype in heterozygous individuals.
