[Campbell Biology P.349] Why are tortoiseshell cats almost always female? | Practice Question

Why are tortoiseshell cats almost always female?

  • A: The gene for coat color is on the Y chromosome.
  • B: The tortoiseshell phenotype requires being heterozygous for an X-linked gene, which is only possible in XX females.
  • C: Male cats with both black and orange fur are sterile.
  • D: The orange fur allele is lethal in males.

Explanation

As explained in Figure 15.8, the tortoiseshell phenotype requires the presence of two different alleles for coat color one for orange, one for black on the X chromosome. Since males are XY, they normally only have one X chromosome and thus can only have one of these alleles being either all black or all orange . Only females XX can have two different alleles and be heterozygous. The patchy pattern then results from random X inactivation in different cell populations.