Task

In cats, the genes for black (Xᴮ) and ginger (Xᵇ) coat colour are on the X chromosome and are codominant: XᴮXᵇ females are tortoiseshell. A tortoiseshell female was crossed with a ginger male. 1) Using this example, explain sex-linked inheritance and codominance. 2) Write the cross, gametes, offspring genotypes and phenotypes; explain why tortoiseshell males are very rare and what genotype they usually have. 3) Give the offspring phenotypic ratio (taking sex into account) and the share (%) of each class. 4) If the pair has 12 kittens, how many tortoiseshell and how many ginger kittens are expected? 5) Calculate the probability (%) that at least one of three kittens is tortoiseshell. For each part, write out the law or method used (cross scheme, formulas, reasoning) and all calculations step by step.