Red-green colorblindness is an X-linked trait. Color vision (XR) is dominant to
ID: 211586 • Letter: R
Question
Red-green colorblindness is an X-linked trait. Color vision (XR) is dominant to red-green colorblindness (Xr). Note that XR is a single chromosome - an X chromosome carrying the allele R for normal color vision. Similarly, Xr is a single chromosome - an X chromosome carrying the allele r for red-green colorblindness.
A. True or false: If a woman displays a sex-linked recessive trait, then all of her sons will display that trait as well.
B.
Cynthia has red-green colorblindness, but her husband, Tom, has normal vision. What are their genotypes?
C,
What are the possible genotypes of their children, Naomi, Nathan and Oliver?
Explanation / Answer
A. True If a woman displays a sex-linked recessive trait, it implies that she carries two mutant alleles on X-chromosomes and a son inherits its X chromosome from his mother only. Hence all the sons of the affected mother will inherit the mutant X-chromosome and will display the trait.
B. Cynthia`s genotype will be Xr Xr and her husband`s genotype will be XR Y.
C. Naomi`s genotype will be Xr XR, Nathan`s genotype will be Xr XR and oliver`s genotype will be Xr Y. Her daughters will be carrier of the trait and sons will be affected.
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