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Probability tree of Biology

GouchnoxGouchnox Posts: 6,337Member, Friendly, Cool, Conversationalist ✭✭✭✭✭✭
It made a thread because there's more room for fat calculi.
(at that moment Gouchnox remembers that no one replies in those threads, nor do they even see them)

In this family tree, the person in II.1 has a genetic disease, that has an average of 1 in 16,000 chance of occurring in a normal population.
What is the probability of III.1 having this disease?
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  • erdbeereerdbeere Posts: 3,360Member, Helpful ✭✭✭✭✭
    What are the rules for inheritance of genetic diseases?
    I searched for some formulae, but only found walls of text without formulae.
  • DarthCookieDarthCookie Posts: 5,618Moderator, Friendly, Helpful, Flagger, Conversationalist Mod
    Is it not 25%?
    Oh, wait, I forgot a "variable", would it be 12.5% (Assuming it's an X chromosome thing like color-blindness. That's 50% chance of being a dude, 50% chance of mother being a carrier and 50% chance of actually receiving the "correct" x-gene.)
  • GouchnoxGouchnox Posts: 6,337Member, Friendly, Cool, Conversationalist ✭✭✭✭✭✭
    To do stuff:
    Based on the fact that II.1 has the disease, and that it's recessive (of course), you can calculate the probability of II.2 being heterozygous. You can do the same thing with the 1/16000 to calculate it for II.3, and then you calculate the chance of III.1 having it.
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  • ZyzzyzusZyzzyzus Posts: 4,255Member, Helpful, Conversationalist ✭✭✭✭✭
    edited January 2015
    Is it caused by a single recessive gene? Is it sex linked?
    erdbeere said:

    What are the rules for inheritance of genetic diseases?
    I searched for some formulae, but only found walls of text without formulae.

    That depends on the disease. For a single gene there is a 50/50 chance of inheriting each allele from a parent. For sex linked genes (one's on the X chromosome) males only have 1 allele and it comes from the mother. When considering multiple genes it becomes much harder since 2 genes close together do not have independent probabilities. But far apart genes are approximately independent.

    I have done some probability theory on this kind of thing but I am too lazy to calculate it. :p

    In the question in the OP, the parents of II.I can't both have the disease. Either 1 does and the other is a carrier or both are carriers. But you are given that II.I has the disease so this alters the probabilities.
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  • Deathranger999Deathranger999 Posts: 1,692Member ✭✭✭
    I could work this out but I'm way too lazy to. ;_;
    "Monotheism is progress of a sort because they're getting nearer the true figure all the time." -C. Hitchens
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  • YaddladdlYaddladdl Posts: 699Member ✭✭✭
    My grandfather devoted his life's work to pedigree charts doing exactly these kinds of calculations. Unfortunately I am not a talented mathematician, so I can't answer the OP either.
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