In certain breeds of hamsters, females can be black, orange, or a black-and-orange mosaic called tortoise-shell, where small patches of black and orange fur are interspersed (see image at right). However, males of these breeds can be either black or orange but never tortoise-shell. For example, in a parental cross between orange females and black males, all of the F1 female offspring are tortoise-shell, but all of the F1 males are orange.
A. Using the information provided above, propose a hypothesis that would explain why tortoise-shell coloration occurs only in females, and briefly explain. As part of your answer, please produce the Punnett square in the space provided for the parental cross described above and explain your notation system (solved)
B. At a second gene locus on a different chromosome, the dominant allele P allows black pigment to be deposited in fur, but the recessive allele p prevents the deposition of black pigment, turning hairs that would normally be black to white. Alleles at this locus, however, have no effect on the deposition of orange pigment. Thus, female hamsters who are homozygous pp recessive can be white, orange, or a white-and-orange mosaic called creamsicle, but never black or tortoise-shell. Males who are pp can only be white or orange. Now imagine a parental cross between a white female and an orange male. The F1 female offspring are all tortoise-shell, and the F1 male offspring are all black. In the spaces below, write the genotypes of parents and F1 offspring for this cross (solved)
c. Now consider a cross between the F1 tortoise-shell females and the F1 black males from part (B) on the previous page. In the spaces below, (1) fill out the complete Punnett square for this F1 cross, and (2) write the number of female and male F2 offspring for each of the five possible coat colors
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