The Amami spiny rat (Tokudaia osimensis) lacks a Y chromosome, yet scientists at Hokkaido University in Japan have reported that key sex-determining genes continue to be expressed in this species. Provide possible explanations for why male differentiation can still occur in this mammalian species despite the absence of a Y chromosome.

In mice, the X-linked dominant mutation Testicular feminization (Tfm) eliminates the normal response to the testicular hormone testosterone during sexual differentiation. An XY mouse bearing the Tfm allele on the X chromosome develops testes, but no further male differentiation occurs—the external genitalia of such an animal are female. From this information, what might you conclude about the role of the Tfm gene product and the X and Y chromosomes in sex determination and sexual differentiation in mammals? Can you devise an experiment, assuming you can 'genetically engineer' the chromosomes of mice, to test and confirm your explanation?

In the wasp Bracon hebetor, a form of parthenogenesis (the development of unfertilized eggs into progeny) resulting in haploid organisms is not uncommon. All haploids are males. When offspring arise from fertilization, females almost invariably result. P. W. Whiting has shown that an X-linked gene with nine multiple alleles (Xₐ, Xb, etc.) controls sex determination. Any homozygous or hemizygous condition results in males, and any heterozygous condition results in females. If an Xₐ/Xb female mates with an Xₐ male and lays 50 percent fertilized and 50 percent unfertilized eggs, what proportion of male and female offspring will result?

The genes encoding the red- and green-color-detecting proteins of the human eye are located next to one another on the X chromosome and probably evolved from a common ancestral pigment gene. The two proteins demonstrate 76 percent homology in their amino acid sequences. A normal-visioned woman (with both genes present on each of her two X chromosomes) has a red-color-blind son who was shown to have one copy of the green-detecting gene and no copies of the red-detecting gene. Devise an explanation for these observations at the chromosomal level (involving meiosis).

When the cloned cat Carbon Copy (CC) was born, she had black patches and white patches, but completely lacked any orange patches. The knowledgeable students of genetics were not surprised at this outcome. Starting with the somatic ovarian cell used as the source of the nucleus in the cloning process, explain how this outcome occurred.

In reptiles, sex determination was thought to be controlled by sex-chromosome systems or by temperature-dependent sex determination without an inherited component to sex. But in the Australian lizard, Pogona vitticeps, it was recently revealed that sex is determined by both chromosome composition and by the temperature at which eggs are incubated. What effects might climate change have on temperature-dependent sex determination in this species, and how might this impact the sex ratio for this species in subsequent generations?