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What causes dominance between alleles?

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

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What causes dominance between alleles?

Postby Fearnot » Fri Aug 09, 2013 4:22 pm

In alleles, what makes one dominant and the other recessive? Why is the transcription of the chromosome that carries the dominant gene preferrable to the one that carries the recessive gene?
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Re: What causes dominance between alleles?

Postby jonmoulton » Fri Aug 09, 2013 7:45 pm

This is not the only way that dominance and recessiveness can happen. But this is a good way to illustrate once possibility (and a fairly common one).

When you have two healthy alleles for a particular gene, one copy on a maternal and one on the corresponding paternal chromosome (and excluding the sex chromosomes), then usually both copies are making transcripts.

Maternal - good protein
Paternal - good protein
Result - plenty of good protein

Now say you have one allele that encodes a defective protein. Since there is still good transcript being made from the healthy allele, you don't see a disease due to lack of the protein.

Maternal - good protein
Paternal - defective protein
Result - some good protein

or

Maternal - defective protein
Paternal - good protein
Result - some good protein


But what happens if both of the alleles encode defective proteins? Now that protein is not being made and a disease can result. This would be a case of the healthy allele being dominant over the recessive defective allele.

Maternal - defective protein
Paternal - defective protein
Result - no good protein **bummer**
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Postby Fearnot » Fri Aug 16, 2013 5:17 pm

Thank you Jonmoulton, ur reply has enlightened me a lot about this topic.
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