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 Genetics Kaplan consanguinity  

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this is from Genetics Kaplan lectures notes.

A man who is a know heterozygous carrier of oculocutaneous albinism mariies his halfcousin (they share one common grandparent). This trait is transmitted as a fully penetrant autosomal recessive. What is the probability that this couple will produce a child with this disorder?

The answer is 1/64.

but I have a question.

If they are not relatives , and in the same case (both heterozygous) the probability that this couple produce a child with that disorder will be 1/4 right?

So it isnĀ“t supposed that consanguinity increase the risk of have the desease?

Does anyone coulp explain me this concept plz?


Hey, alright.. the way you get 1/64th is that..

For every generation of kids on both sides of the male and female families you multiply by 1/2 of the genes being passed on... this means that "grandfather passing on to his son (1/2 of his genes) and grandfather passing on this his daughter (1/2 of his genes)"... from here the son will pass on the genes to the male carrier in question "another (1/2 of genes) and from the cousins mother to her daughter (cousin) would be (1/2 genes)..
i.e. a total gene homogeneity of 1/2 x 1/2 x 1/2 x 1/2

i.e. simplified, for every generation, multiply 1/2 for both sides, grandfather to grandson - 1/2 x 1/2 and grandfather to granddaughter 1/2 x 1/2 .. for a total of ... 1/2 x 1/2 x 1/2 x 1/2 = 1/16 ..

Now we have only figured out how much they have in common so therefore how much the probability is that the woman shares the mutant gene with the male (which we already know he has).. now we have to add on the probability of getting a baby born with a recessive trait.. i.e. "aa"

which means that both parents must pass on the defective gene, which would be a 1/4 chance (as by punnet square) (if mother was a carrier for which we have a 1/16 chance that she is) ... therefore multiply 1/16 by 1/4.. which would give you a total of 1/64..

which is the probability that this child is born with the autosomal recessive trait given...

hope this helps
i hope that helps

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