Question

You are breeding chickens and your friend gives you a grey chicken with yellow legs and a plain black rooster with orange legs. You cross these two and get a bunch of chickens, all of them are grey, and half of them have yellow legs while the other half have orange legs. You are curious about the leg allele so you take two of the grey yellow leg offspring and cross them together and you get 1/4 black yellow legs and 3/4 grey yellow legs. Then you cross two of the grey red legs together, and you get a mix of grey and black chicks with yellow, orange and a new color, red legs. What can you tell me about the relationship between these alleles and the genotypes of the parent chickens? (assume you only have two genes and got enough chicks to see all possible genotypes)

Answer 1

As per the inheritance pattern shown by the chicken, it is autosomal inheritance and the genes are present in different chromosomes and not linked. Because there is independent assortment occurring in the genes.

Suppose we take Grey color as 'G' and black color as 'g'. we considered Grey as dominant because in F1 generation all chicks are grey in color.

Leg alleles Red-R, yellow -r. Red is considered dominant here because in the F2 generation, Red appears when two orange legged chicks are crossed. Orange color is due to heterozygous condition of the alleles for red and yellow.

These are the first cross obtained which we can call F1.

This is one of crosses from F1 individuals. This punnet square clearly shows that the Grey is dominant and black is recessive.

The alleles for leg color are incompletely dominant over each other. That is why it is giving 3 colors when F1 'grey and orange' chicks of F1 generation are crossed. Red and yellow are alleles are incompletely dominant. So when orange color legged chicks crossed, we get yellow, orange and red colored legs in the offspring.

So, RR is red, Rr is orange, rr is yellow. When the gene is in heterozygous condition, it is giving intermediate color orange.

So grey is dominant over black allele. Where as red and yellow are incompletely dominant.

This is the relation between these genes and their alleles.