In cats, orange coat color is determined by the b allele, and black coat color is determined by the B allele. The heterozygous condition results in a coat pattern known as tortoiseshell. These genes are X-linked. What kinds of offspring would be expected from a cross of a black male and a tortoiseshell female? What are the chances of getting a tortoiseshell male?

Verified step by step guidance

1. Identify the genotypes of the parents based on the information given: The black male has genotype X\^B Y (since males have one X and one Y chromosome), and the tortoiseshell female has genotype X\^B X\^b (heterozygous for the B and b alleles).
2. Determine the possible gametes each parent can produce: The male can produce sperm carrying either X\^B or Y, and the female can produce eggs carrying either X\^B or X\^b.
3. Set up a Punnett square to combine the male and female gametes. The rows represent the male's gametes (X\^B and Y), and the columns represent the female's gametes (X\^B and X\^b).
4. Fill in the Punnett square to find the genotypes of the offspring: Combine each male gamete with each female gamete to get the possible genotypes of the offspring (X\^B X\^B, X\^B X\^b, X\^B Y, X\^b Y).
5. Interpret the genotypes in terms of coat color and sex: Females with X\^B X\^B are black, females with X\^B X\^b are tortoiseshell, males with X\^B Y are black, and males with X\^b Y are orange. Calculate the probability of each genotype, and specifically identify the chance of getting a tortoiseshell male (which is not possible because males have only one X chromosome).

Key Concepts

X-linked Inheritance

X-linked inheritance refers to genes located on the X chromosome. Males (XY) have only one X chromosome, so they express the allele present on it, while females (XX) have two X chromosomes and can be homozygous or heterozygous. This pattern affects how traits like coat color are passed and expressed differently in males and females.

Alleles and Phenotypes in Coat Color

The B allele codes for black coat color, and the b allele codes for orange coat color in cats. Females heterozygous for these alleles (Bb) exhibit a tortoiseshell pattern due to X-chromosome inactivation, which causes patches of cells to express different alleles, resulting in a mixed coat color.

Punnett Square and Probability in Genetic Crosses

A Punnett square is a tool used to predict the genotypes and phenotypes of offspring from parental crosses. By considering the X-linked nature of the alleles and the parents' genotypes, one can calculate the expected ratios of black, orange, and tortoiseshell offspring, including the probability of rare phenotypes like tortoiseshell males.