Question

1.) If a male who is color-blind has children with a female who is a carrier for color-blindness, what is the possible phenotypic ratio of their offspring? Use numbers in each blank out of 4 possible offspring: ________ girls with color vision : ________girls without color vision : _________boys with color vision : ________boys without color vision.

2.) If two dihybrid pea plants, PpSs and Ppss (P=purple flowers, p=white; S=starchy seeds, s=sweet), what are the genotypic and phenotypic ratios? Use numbers in each blank out of 8 possible offspring in each blank. Genotypic ratio: [a] PPSs : [b] PpSs : [c] ppSs : [d] PPss : [e] Ppss : [f] ppss; Phenotypic ratio: [g] purple, starchy : [h] purple, sweet : [i] white starchy : [j] white sweet

3.) Sickle-cell anemia is autosomal recessive. Which of the people in this pedigree are definitely carriers? Mark all correct answers.

Answer 1

First we have to remember that color blindness is a X-linked recessive mutation. In males this particular deficiency frequentl, as males have only one X chromosome compared to females which have two X chromosomes. For a male to be affected with color blindness he only needs​ one X chromosome affected; in contrast, females need both X chromosomes to be affected, as if only one is affected the other chromosome is functional, meaning that she will not present the trait, but she would be a carrier of the mutation.

That being said, then 1 out of 4 (1/4) children would be girls with normal color vision, 1/4 would girls with color blindness, 1/4 would be boys with color vision, and 1/4 boys would be boys with color blindness.