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basic misunderstandings

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

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Postby canalon » Sun Dec 18, 2005 2:58 am

Hi Joe,

It's not complication it's precision ;)
At the phenotypic level (expressed) an allele is a trait of the same character, but at the genotypic level an alleles are just the different sequences taht can be found for the same gene. Difference in sequences due to mutation.
Let's take an example. The gene CFTR.
If you sequence one of my chromosome you will find one sequemce, if you sequence you will find a very close but maybe slightly different sequence. But both proteins are perfecty functional. Either because the difference in sequence in DNA lead to the same protein (read about the translation of RNA to protein and synonimous codons) or because the mutation does not impair the way the protein is functionning. 2 genotypic alleles, one trait. Now take someone with cystic fibrosis and you will find a compltetly different thing: there is a huge mutation in both genes that makes either incomplete or faulty protein. The ion channel cannot perform its role and you have a very sick person. Once again 2 alleles (different from the first 2) and one trait. So if you sum up things you have 4 alleeles from the genotypic point of view and 2 traits (phenotypic point of view).

Hope this helps
Patrick

Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)
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basic misunderstandings

Postby joe1401 » Fri Dec 30, 2005 12:15 am

Patrick,

Thanks! I think I get what you are saying, but indulge me a bit more. In the case of the cystic firbosis situation, if I read you correctly, the disease is the result of both alleles being faulty on the chromosomes of the sick person. Does this mean that it takes both alleles to produce a faulty protein? And I'm assuming that "both" refer to the maternal and paternal chromosomes.
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