from gloria stephens
stephens at hq.jcic.org
Sat Jul 15 21:32:27 EST 1995
Thank you for your reply. I am still not comfortable.
In "Genetics a molecular approach' by T A Brown
"In the heterozygote only one allele, the cominant one, contributes to
the phenotype; the ressive allele is, in effect, silent.
The functional version of the gene we designate 'G': it is the correct
version that can be expressed by transcription and translation to produce
a functional gene product. The non-functional form we will designate 'g':
this version contains a mutation that destroys the biological information
carried by the gene so it no longer codes for the functional gene
..can be explained in terms of dominant = active gene and recessive =
inactive gene. This is not always the case and variations on this basic
theme are known:
Incomplete dominance: heterozygous form displays a phenotype intermediate
between the two homozygous forms
Codominance: both alleles are active in the heterozygous state
Multiple alleles: Multiple alleles - like blood type
I deal with domestic feline genetics. May we send a messenger to the cell
to make - chocolate. In the cat world chocolate is recessive to black.
We now have one chromosome from the mother with the recessive 'b' and one
chromosome from the father with the recessive 'b' gene.
To which chromosome does the messenger go?
If it goes to the maternal chromosome first, is mRNA formed from that
chromosome. Is this enough for a complete transcription?
Suppose, on the other hand the paternal chromosome has the dominant gene
B. If the messenger goes to 'b' first, is mRNA formed from 'b' or does
the messenger go looking for the dominant trait?
I understand that if the dominant gene is present, then it is read and
mRNA is formed.
On a molecular basis, what happens?
You say 'that only one strand of the two DNA strands is actually
I understand that. As far as I know, it is not known which strand acts as
a template and which strand is actually transcribed. But, again, my
question concerns both chromosomes, not the strands or the two strands of
the double helix.
Sorry to be brain dead, but this is a question that has bugged me for a
May I return to B and b? In B - no problem, unless there is codominance?
If that is the case, then B and b would have to be transcribed to make a
In the case of b and b, then two polypeptides are transcribed and bonded
to form one polypeptide?
I understand the importance of genetic material coming from both parents
in meoisis and crossing over.
I just want to understand more about mRNA and recessive genes - again -
on a molecular basis.
No, I do not have a Ph D or an MD. Degree in Biology - some time ago. So
what I know, I have taught myself. The only thing, the more I think I
know, the more I find I do not know.
I wish to thank you for helping me to understand.
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