Found this question out there and I didn’t know the answer myself. Thought I’d share…
In humans, one of the genes determining color vision is located on the X chromosome. The dominant form (C) produces normal color vision; red-green colorblindness (c) is recessive. If a man with normal color vision marries a color-blind woman, what is the probability of their having a color-blind son? A color-blind daughter?
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(Brace yourself for an old high school chemistry lesson here in case you forgot)
ok we generally write this as Xc or XC (to show its linked to the X chromosome…the Y has nothing to do with it) Also note the c’s are supposed to be superscript!
The different genotpyes and phenotypes are
XC XC = normal female
XC Xc = carrier female, not affected
Xc Xc = affected female
XCY= normal male
Xcy = affected male
ok so a normal mae (XCY) + colour blind female (XcXc)
Xc : Xc (female alleles)
XC. XCXc XCXc Female all carriers
Y . XcY XcY All males colourblind
Note that its the mother that passes colourblindness to her sons (on the X , the Y is passed from his father and has no influence on the actual presence of the gene), if a male is colourblind then his maternal grandfather will probably also have been colourblind.
Because males only get 1 copy, they are more often to be colourblind than females, which require 2 reccessive alleles (1 from each parent…which is statisically harder to achieve)
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