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pedigree analysis of trait

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

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pedigree analysis of trait

Postby biogirl87 » Thu Oct 26, 2006 11:19 pm

Hi, so if given this pedigree (sorry I don;'t have a picture of it...):

Generation I:
female- normal x male- affected

Generation II (offsprings of that match) and Gen III:
normal female- married to normal male to give 5 normal offsprings (3 daughter, 2 sons)
affected male
normal male

affected male- married to normal female to give a normal son
affected female- married to normal male to give an affected daughter, normal daughter, and an affected son

I hope this is comprehensible, again, sorry for the lack of a diagram.

Okay, so this is a rare genetic disorder, and there's the pedigree.
We have to determine whether it's recessive or dominant ... autosomal o X linked. (or can't be determined from this pedigree)

I ruled out rec and dom X linked because then the offspring patterns of the affected female in generation II doesn't make sense. However, I couldn't rule out either one of the dominant or the recessive autosomal mutations. Am I missing something or is the pedigree in fact not giving enough info?

Thanks!!!
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Postby Dr.Stein » Fri Oct 27, 2006 1:20 am

It is a recessive X-linked genetic disorder ;)
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Postby biogirl87 » Fri Oct 27, 2006 1:40 am

that's not possible because then that means that the affected female in Generation II could not have had an affected daughter.... affected female in generation II should have had X*X* (where X* is recessive mutation), and her husband, since not affected, should have been XY... cross them and you can't get X*X* (ignoring non-disjunction and things like that)... at least thats my understanding...
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Postby Dr.Stein » Fri Oct 27, 2006 2:31 am

Oops sorry I made some mistakes :oops: First I thought it was a X-linked thingy, then I typed it that way. But then I believe it is a recessive autosomal thingy. I forgot to delete the "X-linked" words. And I also forgot to upload my pedigree 8)

Here is my proposal :

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Postby biogirl87 » Fri Oct 27, 2006 3:17 am

Nice pedigree!

Okay, here's the actual reason why I raised this question. This was a question on my test... pedigree was given and the five choices were:

A- a recessive autosomal mutation
B- a recessive mutation on the X chromosome
C- a dominant mutation on the X chromosome
D- a dominant autosomal mutation
E- none of the above can explain the pedigree

At first I guessed recessive autosomal... but then I ended up picking E as my answer because I considered dominant autosomal mutation and it worked just fine as well:

Gen I: aa-Aa
Gen II: aa, aa-Aa (with offsprings: aa, Aa, Aa), aa-aa (with offsprings all aa), Aa, aa-Aa (with offspring aa)

Correct me if I'm wrong, but that pattern works as well (in the order you've given in your pedigree)? (that is, if A is the dominant mutation and therefore aa will be the wild type and Aa or AA will be the affected ones)

And either way... you get a roughly expected ratio of offsprings don't you? For instance, in the recessive, since you crossed a heterozygote and a homozygote GI parents, you roughly expect half affected individuals and half carriers (displaying normal phenotype).... in the dominant, in the same cross, you're also expecting roughly half affected individuals (heterozygotes) and half normal individuals.... I looked at the ratio for all the crosses and it seemed to work out fine either way...

I just want to ask for opinions from others before I should go ask my professor and make sure I'm not missing something really obvious...
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Postby Dr.Stein » Fri Oct 27, 2006 1:07 pm

Well, as you may know, Genetics is not my major. Thus, I think that's all I can do for you ;)
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