A pedigree

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

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mensamedlem
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A pedigree

Post by mensamedlem » Tue Dec 01, 2009 12:21 pm

Please help me with this pedigree.

a) What is the mode of inheritance? Why?

b) What are the genotypes for each individual (a = sick and A = healthy)?

http://www.flickr.com/photos/[email protected]/4150173426/

mensamedlem
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Post by mensamedlem » Tue Dec 01, 2009 7:09 pm

Is this correct?

(a) Autosomal recessive
First we look at why it is recessive.
I'll use your "healthy" and "sick" instead of "normal" and "mutant" in the following explanation.
II-3 and II-4 are healthy, III-1 and III-2 are sick.
For dominant, sick offspring can only be produced by sick parents.
So dominant inheritance is ruled out.

Then we look at whether it is X-linked recessive or autosomal recessive.
If it is X-linked, II-2 must have inherited a mutant X from I-1 and another from I-2.
This is not true because I-1 is healthy (remember, for X-linked, as long as a male has a mutant allele, then he is sick).

So in conclusion this is autosomal recessive.

(b) I-1 and I-2 can produce sick offspring, but themselves are healthy. Therefore they are carrier, genotype: Aa

II-1 can either be Aa or AA.
II-2 is sick, so she must be aa.
II-3 can produce sick offspring with II-4, so both of them are carrier with genotype Aa.

III-1 and III-2 are sick, so they are aa.
III-3 can be Aa or AA.

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