Predictability of Color Deficiency

color deficient males cannot have color deficient children (unless their spouse is a carrier...). BUT: exactly 1/2 of the male GRANDCHILDREN born to the DAUGHTERS of a color deficient person will be color deficient. so *this* really *is* one of those things that "skips a generation", unlike having twins. twins "skipping a generation" is a myth.

color deficiency is carried on the X chromosome. males are XY & females are XX. when a color-deficient male has a son, those males got their normal (not color-deficient) X from their mother and their Y from the color-deficient father, but the Y doesn't carry the color-deficient gene. Almost ALL males born to a color-deficient male will be normal-color-vision (the rare exception would be if the mother was also a carrier from a color-deficient father from another, different bloodline/genepool).

when a color-deficient male has a daughter, the daughter gets one X from their mother & the "defective" color-deficient X from their color-deficient father. these females will be "carriers" for color-deficiency but will not be color-deficient (b/c they have a "normal" X from their mother).

so none of the children of a color-deficient male will be color-deficient, unless the mother was a carrier.

however its when the daughters of color-deficient males have male children...thats when it gets interesting. if the daughters of a color-deficient male have SONS...there is a 50/50 chance those males will be color-deficient, b/c there's a 50/50 chance that the X they get from their mother will be the color-deficient X.

also, 50% of female offspring of color-deficiency carriers will also be carriers (but won't be color-deficient themselves), so 50% of THEIR sons will be color deficient as well.

got your brain wrapped around THAT yet? :D

now lets talk about eye color & "incomplete dominance" just kidding. the short version is: no one can predict eye color based on the eye color of the parents b/c of an uber-complicated genetic pattern called "incomplete dominance" that eye color genes exhibit. patients want me to "predict" the color of their baby's eyes...but b/c of incomplete dominance its impossible to do so. no one can.


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