Question on Genetics: Fitness

[starbaduk]

This is from TPR BS Review book:

"If a recessive allele causes sterility in homozygotes, how will it affect the fitness of heterozygotes?"

TPR Answer: "IF the allele is truly recessive, it will not affect fitness at all. Natrual selection can act only on phenotypes, not genotypes"

I thought fitness was an ability to pass on its genes to future generations. So, wouldn't heterozygote's genotype affect the fitness of F1 generation by increasing the probability of F1 offsprings being sterile (compared to if he was homozygote dominant)? Since his F1 offsprings have half of his genes, wouldn't this affect the fitness of the original individual?

I'm a newbie at genetics stuff. Help would be appreciated. Thanks~

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[muchomaas]

Im not positive, but I think the point is that the heterozygote's fitness is not affected since his fertility is not affected.

It's a fair point to clarify that fitness does not refer to the gene's fitness, or its fitness in perpetuity, but solely to the individual who possesses the gene, which is what a phenotype is, in a way

basically I believe you read too far into the problem and shouldn't be considering the F1.

 

[funsmith]

Fitness IS the ability to pass on genes but how capable an organism is at doing this up to a certain degree dictated by the quality of his genes. Natural selection does indeed select only on the phenotypes. Even though it is the manifestation of a component of the genotype.

Assuming that there is no haploinsufficiency then the gene would have no effect on the organism's sterility.

It is nevertheless true that the genes do affect phenotype but phenotype is the result of genotype and environment. A recessive copy of the gene would not hinder the WT expression of the gene product in the organism. Hence, the dominant copy of the gene would still express the normal protein and thus no sterility.

I hope this helps. I hope I didn't just blabber on about nothing.

 

[zayka]

When talking about fitness of a particular individual, like in this question, it is assumed that you care about the heterozygote only (not its babies). If it asked about the allele in general, it would probably disappear from the population over the long haul. But yeah, only care about that one individual they asked.

 

[zayka]

Fitness IS the ability to pass on genes but how capable an organism is at doing this up to a certain degree dictated by the quality of his genes. Natural selection does indeed select only on the phenotypes. Even though it is the manifestation of a component of the genotype.

Assuming that there is no haploinsufficiency then the gene would have no effect on the organism's sterility.

It is nevertheless true that the genes do affect phenotype but phenotype is the result of genotype and environment. A recessive copy of the gene would not hinder the WT expression of the gene product in the organism. Hence, the dominant copy of the gene would still express the normal protein and thus no sterility.

I hope this helps. I hope I didn't just blabber on about nothing.

Wow, lots of extra info

 

[vickpick]

ok.. i see.. it is talking abt a different allele.. lol...

yea then, if its recessive then there is no effect..

 

[0Complications]

Typically, whenever you're given questions that strongly infer homozygous and heterozygous characteristics they are just getting at basic Mendelian Genetics. Think dominant, recessive, genotype, phenotype.

Don't make these questions more difficult than they are. They should be gravy points.