In certain breeds of chicken, feather colour is an illustration of codominance in birds.
Here, a white-feathered chicken and a black-feathered chicken can mate and produce offspring with both white feathers and black feathers.
The allele for black feathers is $F^{B}$ and the allele for white feathers is $F^{W}$.
Fig. 5.1 shows a pedigree diagram for a chicken family.
(a)[1]
State the type of variation that is controlled only by genes.
(b)[2]
State all possible genotypes for chicken 2 and chicken 7 in Fig. 5.1.
(c)[5]
Complete the genetic diagram to show the outcome of a cross between chicken 5 and chicken 6 in Fig. 5.1.
parental phenotypes [BLANK] \times [BLANK]
parental genotypes [BLANK] \times [BLANK]
gametes [BLANK], [BLANK] [BLANK], [BLANK]
offspring genotypes [BLANK]
predicted offspring phenotype percentage [BLANK]
(d)[1]
State one example of codominance in humans.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “discontinuous variation” …