In Syrian hamsters, males are XY and females are XX. A gene on the X chromosome controls fur colour. The allele Y Y\,Y codes for yellow fur and the allele B B\,B codes for black fur. These alleles are codominant. Heterozygous females have yellow and black patches of fur and their phenotype is described as tortoiseshell female. The two alleles, S S\,S and s s\,s of a different gene, which is not sex-linked, interact with the gene controlling fur colour. The allele S S\,S is dominant and stops the formation of pigment in the fur, resulting in white fur. The allele s s\,s is recessive and has no effect on fur colour.
Name the type of interaction between the two genes affecting fur colour.
What phenotype would a hamster with the genotype XYXBss X^Y X^B ss\,XYXBss have?
Complete a genetic diagram to show all the possible genotypes and the ratio of phenotypes expected in the offspring of the cross: XYXYSs×XBYssX^Y X^Y Ss \times X^B Y ssXYXYSs×XBYss.
In a population of these hamsters, 19% of hamsters had the S S\,S allele and had white fur. Use the Hardy–Weinberg equation to calculate the frequency of the s s\,s allele in this population. Show your working.
