Re: What is a recessive gene?

Gary Bohn wrote:
> "hersheyhv" <hersheyh@xxxxxxxxxxx> wrote in
> news:1137952785.317644.62850@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:
>
>
>>Gary Bohn wrote:
>>
>>>What is your favourite colour?
>>>What is the air-speed velocity of an unladen swallow?
>>>
>>>Sorry.
>>>
>>>I've been playing with the Hardy-Wienberg equation to see how
>>>selection can actually work in a population and suddenly realized I
>>>have no idea of what makes a recessive allele recessive. What
>>>attributes does the recessive allele have that makes it less likely
>>>to be expressed or what attributes does the dominant allele have that
>>>makes it more likely to be expressed?
>>
>>Actually it is not the *gene* that is recessive. It is the
>>*phenotype* that that gene plays a role in generating. The way to
>>detemine *if* an allele (one form of a gene) has a dominant or
>>recessive *effect* is to create a heterozygote, a diploid individual
>>with two *different* alleles or forms of the same gene (call this the
>>A/a state) and observe one of the *phenotypes* that that gene is
>>responsible for and compare that to the *phenotypes* produced when
>>both alleles are the same (the A/A and a/a states). The allele, which
>>produces the same phenotype in both the heterozygote and the
>>homozygote (say the A/a and A/A states), is called "dominant". The
>>other allele is recessive to the dominant A allele.
>>
>>The reason for dominance generally has to do with the fact that the
>>phenotypes being looked at are relatively distant from the genes
>>themselves and the fact that *functional* genes often have the
>>capacity to produce the same amount of gene product whether or not it
>>is present in a single or two copies.
>>
>>Keep in mind that dominance and recessiveness is purely a phenotypic
>>description. The same alleles can be dominant for one phenotype,
>>recessive for another, and intermediate or co-dominant for a third.
>>In general, the closer the phenotype is to the actual genes and its
>>products, the greater the probability that the relationship will be
>>co-dominant. DNA sequence information is almost always co-dominant
>>(with large deletions being an exception).
>>
>>Take sickle cell for example:
>>
>>At the level of DNA sequence or protein, the relationship between S
>>(the sickle allele) and A (w.t.) is c-odominance. That is, the
>>heterozygote exhibits the presence of both A and S proteins and thus
>>differs from either the A/A or S/S state.
>>
>>The phenotype of sickle cell disease is recessive. That is, the
>>heterozygote A/S does not exhibit the disease and S is, for this
>>phenotype, recessive to the w.t. allele A.
>>
>>Under very low (non-physiologic) level of O2, however, the phenotype
>>of the heterozygote in terms of sickling of cells resembles that of
>>the S/S individual.
>>
>>Thus, depending on the phenotype you are examining, sickle cell is
>>co-dominant, recessive, or dominant. Those terms are descriptive, not
>>inherent features of a sequence.
>>
>
>
> Thanks HH, this goes a long way toward correcting my misunderstanding.
> From here I'll do some more digging.
>

What kept you from digging on google in the first place?


--
Nicolas

"The reason the theory of evolution is so controversial is that it is
the main scientific prop for scientific naturalism. Students first learn
that "evolution is a fact," and then they gradually learn more and more
about what that "fact" means. It means that all living things are the
product of mindless material forces such as chemical laws, natural
selection, and random variation. So God is totally out of the picture,
and humans (like everything else) are the accidental product of a
purposeless universe. Do you wonder why a lot of people suspect that
these claims go far beyond the available evidence?" Phillip E.Johnson,
The Church Of Darwin

.

Relevant Pages

  • Re: What is a recessive gene?
    ... >> have no idea of what makes a recessive allele recessive. ... > *phenotype* that that gene plays a role in generating. ... > Keep in mind that dominance and recessiveness is purely a phenotypic ...
    (talk.origins)
  • Re: What is a recessive gene?
    ... > of what makes a recessive allele recessive. ... > attributes does the dominant allele have that makes it more likely to be ... Keep in mind that dominance and recessiveness is purely a phenotypic ... The same alleles can be dominant for one phenotype, ...
    (talk.origins)
  • Re: Hamiltons rule
    ... does the altruistic phenotype come into play? ... >> It is the frequency of the allele in donors as a class. ... If the allele is dominant, ...
    (sci.bio.evolution)
  • Re: What is a recessive gene?
    ... >>>other allele is recessive to the dominant A allele. ... >>>Keep in mind that dominance and recessiveness is purely a phenotypic ... The same alleles can be dominant for one phenotype, ...
    (talk.origins)