Question

Sally's brother is color-blinded. her husband is normal. what is the chance for her son to be color-blinded?

Answer 1

The inheritance of colorblindness gene is X linked. Sally is a female, she'll have two copies of X chromosomes. Since she is not colorblind indicates that she is a carrier of the gene, the presence of at least one functional gene on either of the X chromosome in Sally prevented colorblindness in her. The chances that her husband will have a colorblind child is 25% (1:3) and 50% for the colorblind son (1:1),based on the solved punnett square in the image, where X' denotes the colorblindness gene.