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Quick question for any Genetists out there...

Discussion in 'Other Off Topic Forum' started by Auraraptor, Oct 4, 2004.

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  1. Auraraptor

    Auraraptor F1 World Champ
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    #1 Auraraptor, Oct 4, 2004
    If the penetrance rate is 80%, does this imply that concordance rate for mono. twins will be .80?

    Thanks.
     
  2. Auraraptor

    Auraraptor F1 World Champ
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    #2 Auraraptor, Oct 4, 2004
    Or would it imply that Concordance = (0.80 x 0.80) + (0.20 x 0.20) = 0.68? (Chance that both sibs are expressive of the same trait...ie each has an 80% chance of expressing the mutant phenotype, so the chance they both match would be .8 x .8; alternately they each will match expressing the wild type .20 x .20 of the time, making the net .68)
     
  3. tbakowsky

    tbakowsky F1 World Champ
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    #3 tbakowsky, Oct 4, 2004
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  4. Auraraptor

    Auraraptor F1 World Champ
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    #4 Auraraptor, Oct 4, 2004
    LoL! It's a shot in the dark, but no one I can think of that knows the answer is awake at this time...so I might as well try here. :p
     
  5. mdo

    mdo Karting

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    #5 mdo, Oct 5, 2004
    a penetrance of 80% means that 80% of those that have the mutant genotype will express the mutant phenotype, i.e. that they will show that they are mutant. It also depends as to whether the disease is sex-linked or autosomal...that will determine your odds as well. The genotype of the parents will also determine what the odds are of the children getting said disease. Give me the necessary info (parents' genotype [i.e. are they carriers or do they possess] and whether what you are looking at is autosomal Dominant or recessive, etc) and i can work it out for you.

    Good ol' Cornell University Genetics 281...lol.
     
  6. Auraraptor

    Auraraptor F1 World Champ
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    #6 Auraraptor, Oct 5, 2004
    All they give me is the following:

    Determine the %C for Monozygotic and Dizygotic twins with respect to:

    A) trait is recessive allele tt based with a penetrance of 80%

    B) trait is determined by dominant allele U_ with a 50% penetrance

    C) Determined by a cominbination of U_ and tt and overall penetrance of 30%
     
  7. Auraraptor

    Auraraptor F1 World Champ
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    #7 Auraraptor, Oct 5, 2004
    For (A) I said:

    Concordance = (0.80 x 0.80) + (0.20 x 0.20) = 0.68 for MZ. DZ = 1/4 x MZ, or DZ = .17

    For (B) I said:

    Concordance = (0.50 x 0.50) + (0.50 x 0.50) = 0.50 for MZ. DZ = 3/4 x MZ, or DZ = .375

    For (C) I said:

    Concordance = (0.30 x 0.30) + (0.70 x 0.70) = 0.58 for MZ.
    Not sure about DZ, it is either
    DZ = (3/4)(1/4) x MZ, or DZ = 3/16MZ = ~.11

    or maybe
    DZ = 3/4MZ + 1/4MZ = .58 ...which does not seem right, so I went with the above.

    I am not sure though if I should be adding the second term for each %C (the + (0.20 x 0.20) for A, or the (0.50 x 0.50) for B etc)
     
  8. zjpj

    zjpj F1 Veteran

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    #8 zjpj, Oct 5, 2004
  9. Auraraptor

    Auraraptor F1 World Champ
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    #9 Auraraptor, Oct 5, 2004
    I may have been right the first time through...namely Penetrance = %C of a MZ. Go figure.

    I take this since %C of Id. Epilepsy is ~.84, which happens to correspond to its Penetrance rate by some sources.

    Ah but wait, some sources say that Id. Epilepsy's P = .90; which would give a .82 %C by my calculations....

    ..damn it.
     
  10. F40

    F40 F1 Rookie

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    #10 F40, Oct 5, 2004
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  11. Forzaholics Anonymous

    Forzaholics Anonymous Formula Junior

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    #11 Forzaholics Anonymous, Oct 5, 2004
    Monozygotic twins come from a single fertilized egg and therefore should exhibit the penetrance in an identical manner. One would ASSu&me that both genotypes would behave as one single genotype in one single organism since they are identical and therefore %C should = Penetrance. This does not factor in things like "developmental noise or environmental factors.

    I'd assume that the question is asking for %C WRT a single type whether wild or mutant as opposed to total %C WRT all possible genotypes. How clear is the question? I'd give as detailed an answer as possible to cover all bases. That was my CYA strategy on short answer exams in grad school.

    Dizygotic Twins come from separate fertilized eggs and therefore really are two different organisms WRT genotype. I'd argue that %C = penetrance^2 * proportion of offspring carrying the dominant allele for this part of the question(s).

    Man, what the hell am i doing up past midnight dealing with this s**t?? I'm supposed to be hounding sponsors for a OEM spec fuel pump for a grumpy old 308 :D
     
  12. UroTrash

    UroTrash Four Time F1 World Champ
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    #12 UroTrash, Oct 5, 2004
    Does this mean we can all post our homework on here and get smart people to solve it?
     
  13. Auraraptor

    Auraraptor F1 World Champ
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    #13 Auraraptor, Oct 5, 2004
    Yes. :)
     
  14. Auraraptor

    Auraraptor F1 World Champ
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    #14 Auraraptor, Oct 5, 2004
    Incidently, the professor agrees that my way in post #2 is the right way of doing it. :cool:
     
  15. MarkG

    MarkG Formula Junior

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    #15 MarkG, Oct 5, 2004
    The Josef Mengele Institute for Genetic Research in Brazil might be able to answer your questions......seems the study of twins was of special interest to him.
     

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