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 (black and white spotted).
The correct answer and explanation is :
Answer:
- Genotypes and Phenotypes:
- BB (Homozygous Black): Black feathers
- WW (Homozygous White): White feathers
- BW (Heterozygous Erminette): Black and white spotted feathers
Explanation (300 Words):
In chickens, feather color is controlled by codominance, which means that both alleles (B for black and W for white) are fully expressed in heterozygous individuals. Unlike complete dominance, where one allele completely masks the other, codominance results in a phenotype that shows both traits simultaneously.
When a chicken inherits two black alleles (BB), it will have black feathers. Similarly, if it inherits two white alleles (WW), it will have white feathers. However, if the chicken inherits one black allele and one white allele (BW), neither color is dominant over the other. Instead, the bird exhibits erminette coloring, where both black and white feathers appear in a spotted or speckled pattern.
Genetic Crosses:
- BB × WW Cross (Black × White)
- Offspring Genotype: 100% BW
- Offspring Phenotype: 100% Erminette (black and white spotted)
- BW × BW Cross (Erminette × Erminette)
- Offspring Genotypes: 25% BB (black), 50% BW (erminette), 25% WW (white)
- Offspring Phenotypes: 25% black, 50% erminette, 25% white
Significance of Codominance:
Codominance is an important genetic principle as it explains how multiple alleles can contribute to a phenotype without one being completely dominant over the other. This is seen in various organisms beyond chickens, such as in human blood types (AB blood type). Understanding codominance helps in predicting genetic inheritance and is fundamental in breeding and genetic studies.
In summary, codominance in chickens results in an intermediate phenotype (erminette) where both parental traits appear distinctly, illustrating the unique nature of genetic inheritance.