Pedigree

Genetics as it applies to evolution, molecular biology, and medical aspects.

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greece_italia
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Pedigree

Post by greece_italia » Thu Oct 18, 2007 1:16 am

#1 is to determine what type of inheritance is involved.

My ans: autosomal recessive

#2 is to write the genotype for each individual using A for normal pigmentation and a for albinism and if genotype is unknown, A_

This is where I'm having a bit of difficulty.
My ans:
Gen I: Aa Aa AA aa
Gen II: A_ Aa aa Aa Aa Aa AA
Gen III: A_ A_ aa A_ A_

#3 is to determine the probability that the marriage between individuals III-1 and III-5 will produce albino children.

I'm not sure about this either.
My methodology would be to first find the probability that these individuals are carriers and then the probability that they would produce albino children. I would use a punnett square to find out the probability that they are carriers but if I don't know the genotypes (considering I am right in #2), how do I do this?

Thanks
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canalon
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Post by canalon » Thu Oct 18, 2007 1:44 am

You cannot really know if II-2 and II-7 are Aa or AA and as a consequence there is no way to be 100% sure of III-1, III-4 and III-5's genotypes.

The method is correct and you have only 2 choices: either you research the probability to be a healthy carrier of the albinos gene in the general population and use it to calculate the probability of carriage of albinism for those individuals. Or you assume that it is to small to be relevant, and just assume that they are AA. Note that II-2 has only 50% of being Aa
Patrick

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any proof. (Ashley Montague)

greece_italia
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Post by greece_italia » Thu Oct 18, 2007 2:53 am

Assume that III-1 and III-5 are AA?

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canalon
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Post by canalon » Thu Oct 18, 2007 12:59 pm

No! II-1 and II-7, the non-members of the family. because you cannot really know if they are aA or AA, but the probability to be acrrier is probably small enough to be neglected compared to the original family.
Patrick

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Post by greece_italia » Thu Oct 18, 2007 11:01 pm

Ok I understand. So I can assume II-1 and II-7 as AA, but what about II-2? If it has 50% chance of being Aa... how do I determine which one to use in the punnett square?

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Post by canalon » Fri Oct 19, 2007 5:34 pm

You just calculate the probabilities with the 2 different possible genotypes and calculate the weighted average (in this case 50% / 50%) of the 2 outcome to get the final probabilities.
Patrick

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