Crossing over

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protozoan
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Crossing over

Post by protozoan » Tue Aug 30, 2005 9:32 am

Have question. How much is known about this process? I read only that the exchange of material of chromosomes occurs. But how exchange? Exchange of hole sequences in frame of one gene or what? If im thinking about mendelian genetics for example we have given one recessive allele and one dominant allele, these alleles are genes which have different sequences of nucleotides, one of these gene is transcribed (dominant) and one isnt(recessive)(why? this is good question too) each are in one chromosome of two homologous pair of chromosomes. Then if there occurs exchange of genetic material (in meiosis) then these genes must mix in and must origin whole new allele. But this is not mendelian genetics cause there genes are not mixed.
Now guys try to let me undestand.
When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth. (Sherlock Holmes)

rambobala
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Post by rambobala » Tue Aug 30, 2005 10:07 am

hi friend,
you had asked three questions

from last to first

1.mendelian genes interaction:
as you always know,genes are transcribed and then expressed.both alles of mendelian gene (dominant and recessive )will be transcribed and result in two diffrent enzymes one will be functional(dominant) other will not be functional(recessive) leading to expression.if both are dominant alleles we see expression and if not in case of recessive we see no expression means transcription is there but mutant or recessive enzyme is non functional.incase of the hybrid f1 as in the case of any heterozycotes we get phenotype as expression since we get functional enzyme.but genotypically we get unlike allees.both of them will get transcribed but one will give a functional protien.
regarding crossing over:
crossing over takes place by the mechanism of crossing over that is homologus recombination in which theoritically no single base pair will be lost.but still there are errors leading to variation thus we gent different phenotypes.

evolution:
previously there is one genotype dominant in case of a single mendelian gene,but due to mutation or errors in crossing over we got recessive (non functional) which are transcribed to give small expression or nil

protozoan
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Post by protozoan » Wed Aug 31, 2005 12:02 pm

Hello friend
The first i see now, but still i see that if two genes will recombinate the new sequence of nucleotides must origin thus two new alleles with new phenotype must arise. These new alleles will give new order of aminoacids in proteins which they are coding. This i think cannot work cause in mendelian genetics one gene (allele) can be inherited through many generation in nonalter form. Where is recombination there?
Very little infos on that process at molecular level is accesible. And i hate to read only one or two sentences which explain nothing.
When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth. (Sherlock Holmes)

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