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 black and orange 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, showing all possible combinations of offspring genotypes: cross X\^B and Y from the male with X\^B and X\^b from the female.
4. Analyze the genotypes of the offspring: Female offspring will be either X\^B X\^B (black) or X\^B X\^b (tortoiseshell), and male offspring will be either X\^B Y (black) or X\^b Y (orange).
5. Calculate the probability of each offspring type by counting the number of each genotype combination and dividing by the total number of possible offspring; specifically, note that tortoiseshell males (X\^B X\^b Y) are 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 have one X and one Y chromosome, so they express the allele present on their single X chromosome. Females have two X chromosomes, allowing for heterozygous combinations that can produce unique phenotypes, such as tortoiseshell coat color in cats.

Alleles and Phenotypes in Coat Color

The B allele codes for black coat color, while the b allele codes for orange. In heterozygous females (Bb), both alleles are expressed in different cells due to X-chromosome inactivation, resulting in the tortoiseshell pattern. Males, having only one X chromosome, show either black or orange but not tortoiseshell.

Punnett Square and Probability in Genetic Crosses

A Punnett square helps predict offspring genotypes and phenotypes by combining parental alleles. For X-linked traits, it is important to consider the sex chromosomes separately. Calculating the chances of specific phenotypes, like tortoiseshell males, involves analyzing possible allele combinations and their associated probabilities.