The pedigree below shows the inheritance of red-green colorblindness, an X-linke

Question

The pedigree below shows the inheritance of red-green colorblindness, an X-linked recessive trait (XD = normal vision, Xd = colorblindness allele). For all of the questions below, assume that there is no abnormal event or new mutation; also, ignore X-inactivation for this problem. Below each individual (except III-1), write out their genotype for color vision. Use "?" to indicate any allele about which you are uncertain. What is the probability that III-1 will be colorblind? Explain your reasoning to show how you arrived at you answer. Using long and short chromosomes for the X and Y, respectively, diagram the sex chromosomes as they would appear in a proper metaphase I of meiosis in individual II-3 of the pedigree above. Be sure to mark the colorvision locus where you think it could be located.

Explanation / Answer

XDXd (carrier female) (1/4)

XD (1/2) Xd (1/2) XD (1/2) XDXD (normal female) (1/4)

XDXd (carrier female) (1/4)

y (1/2) XDy (normal male) (1/4) Xdy (colourblindness male) (1/4)

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