Question

8. In chickens, brown feathers are dominant over red feathers. Suppose we cross two heterozygous chickens.

Answer 1

Answer:

Crossing two chickens heterozygous for the trait feather color, when brown feathers are dominant over red feathers, will produce offspring with brown and red feathers in a brown:red phenotypic ratio of 3:1.

Explanation:

Knowing that in chickens brown feathers are the expression of the dominant allele (B) and the recessive allele is red (b), crossing two heterozygous individuals (Bb) will result in offspring that are likely to have brown or red feathers.

The cross can be represented by a Punnett Square:

Bb X Bb cross

alleles     B    b

B             BB Bb  

b             Bb bb

Where the result is:

Genotypes:  

• Bb, 50%
• BB, 25%
• bb, 25%

Phenotypes:

• Brown feathers, 75%
• Red feathers, 25%.

In this case, the probability of having brown or red feathers is 3:1.