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Genetics question

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

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Genetics question

Postby biouser123 » Tue Oct 31, 2006 11:08 pm

In the case of complete dominance, how does the cell know which allele is dominant over the other. Thx
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Postby druid » Wed Nov 01, 2006 1:52 am

The other is fully inactive. The product of only one allele - dominant allele - is functional.
For example, deletion of a locus on one of two homologeous chromosomes will make the second allele fully dominant ( if it's homosufficient ).
Say, A codes for RED eyes, a codes for BLUE eyes. A heterozygote, A/a will produce red-blue color of eyes ;).
Now if deletion of a occurs than A's product will be only pigment which will paint eyes in red, without blue pigment interference.
Last edited by druid on Wed Nov 01, 2006 2:03 am, edited 1 time in total.
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Postby biouser123 » Wed Nov 01, 2006 2:01 am

so the recessive allele is inherently inactive... if so what will be the case with two recessives or like the case u mentioned. if it is inactive how can it be used to code for a protein. :?:

Also can you please explain what homosufficient is. Thanks a lot.
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Postby druid » Wed Nov 01, 2006 2:07 am

With two recessives no protein will be produced. So no pigment - neither red nor blue will be produced at all and eyes` color will be let me assume transparent ;)

Homosufficient is when product of only one allele is sufficient for phenotipic trait to appear. Well, the example doesn't require usage of this term.
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Postby druid » Wed Nov 01, 2006 2:21 am

Of course if two alleles are recessive and protein for which they code is necessary for living ( smth like pyruvate dehydrogenase ), the creature will die..
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Postby druid » Wed Nov 01, 2006 2:26 am

Moreover, even heterozygote may die. Suppose A/A produce enzyme E. Heterozygote A/a will produce only half of amount of E in homozygote A/A. If half of amount of enzyme E is insufficient for living, we'll soon go to funeral of heterozygote. That's a case when allele A homoINsufficient.
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Postby biouser123 » Wed Nov 01, 2006 2:29 am

druid wrote:With two recessives no protein will be produced. So no pigment - neither red nor blue will be produced at all and eyes` color will be let me assume transparent ;)


I thought that if there were 2 recessives then the color of the eyes will be blue....... so how can we can get transparent eyes?
Thanks for your help
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Postby druid » Wed Nov 01, 2006 2:51 am

"Say, A codes for RED eyes, a codes for BLUE eyes. A heterozygote, A/a will produce red-blue color of eyes.
Now if deletion of a occurs then A's product will be only pigment which will paint eyes in red, without blue pigment interference."
I hope you agree with that.

Now suppose there occured two deletions - of A allele and of a allele. Do you agree with me that NO genes produce NO their products? ;) Therefore by no means eyes can be blue, because a was deleted and cannot produce protein which gives eyes blue color. The same is about A allele. So what do we get? We get no pigments that can paint eyes. What color can eyes be if there's no pigment that can paint them? But you are right - they will not be transparent ( note, i gave smile ) because there is one billion things in eye that prevent it from being transparent ;)
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Postby biouser123 » Wed Nov 01, 2006 10:58 pm

hmm... ok i think i understand the explanation. so u are saying that the recessive allele is deleted from its locus, if there is a dominant allele in the cell. is that even possible; if not is there something like a marker that infront of the gene that tells a cell that it is the dominant one.
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Postby druid » Thu Nov 02, 2006 12:03 pm

biouser123 wrote:the recessive allele is deleted from its locus, if there is a dominant allele in the cell.


There are many ways by which one allele can be made recessive relative to other. It has not to be obligately deletion. For example, gene A produces pigment for RED color, allele a produces pigment for BLUE color. Suppose RED pigment can catalize degradation of BLUE pigment. Then blue color of eyes can appear only in homozygous a/a. Why not in heterozygous? A will produce pigment for red color AND a will produce pigment but for blue color. Because red pigment will degrade blue pigment (AFTER both have been synthesyzed ) phenotype will be RED. Here dominance of A is determined NOT by deletion of homologeous allele but by dominance of PRODUCT of A over PRODUCT of a.

is there something like a marker that infront of the gene that tells a cell that it is the dominant one.


No, there is not such a marker. It's like in sport - you are not born with champion medal, you must PROOVE your dominance in struggle.
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Postby biouser123 » Thu Nov 02, 2006 9:06 pm

Okay that makes more sense. Thanks a lot for your help :D
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