can you explain why natural selection acts on the phenotype rather than on the genotype of an organism?

Answer 1

Why?

Because of the way it has all turned out, an outcome created by changes in a system (our universe) where there seem to be some parameters controlling its behaviour at a deep, fundamental level.

The phenotype is the carrier of a piece of information for building a new phenotype of a similar kind. Carriers tend to live for limited amounts of time, but if they build a new one before dying, at least a fair amount of their genotype might survive. It might even turn out to be a better 'recipe' for that environment.

The idea of natural selection came about before we had any good explanation of what genes actually are, and refers to organisms in environments. But we can apply the principle to DNA, RNA and how these pieces of molecular information came about, stayed around and evolved.

Answer 2

The genotype is the sum total of all the genes in an organism. But not all of those genes are *expressed*. The phenotype is that subset of the genes that are expressed. Since unexpressed genes provide neither advantage nor disadvantage ... natural selection cannot act on unexpressed genes ... only on expressed genes (the phenotype). Reproductive and geographic isolation is when a a subpopulation gets isolated from other members of its species. Geographic isolation causes reproductive isolation (this is called 'allopatric speciation') but there are also ways that members of the same species might not be geographically isolated, but are still reproductively isolated (e.g. if members of a species begin specializing in two different niches in the same geography ... say one takes to the small nuts in the high branches, and the other takes the larger nuts that fall to the ground. In either case, if the two subpopulations do not interbreed or are geographically separated so they can't interbreed, then enough genetic changes will accumulate to where they are biologically unable to reproduce together (and produce fertile offspring). At that point the two subpopulations are technically two species (unable to interbreed) ... so speciation has occurred.

Answer 3

Because natural selection works by selecting traits that have some advantage over ones that have disadvantage.

If a gene is not expressed (i.e. it is recessive, and therefore in the genotype but not the phenotype of the invididual), then it is neither an advantage nor a disadvantage to have that gene. So natural selection cannot act on it. Natural selection can only act on phenotype (the genes that are actually expressed).

Answer 4

I guess it could act on genotype if the selection factor caused mutations. Let's say we screw up the environment so bad that we all get such high doses of UV radiation due to the ozone layer. That will cause mutations in the DNA and cause a change in the genotype right? I'm just thinking aloud here........


But most of the time, it is other environmental factors that are causing the pressure so that's why it is more about phenotype than genotype.

Answer 5

It's a trick question, sort of. The genotype could include a recessive allele or two, and natural selection doesn't select between certain crossings such as (genotype) AA and Aa, or Bbb BBb, simply because either is fit, because in this case, the dominent allele takes over the recessive allele (each animal has the same trait (phenotype) to be seelcted for)

Answer 6

genotypes aren't always detectable.

For example, I have a cat, she is dd (double recessive for the dilution gene- it means she is a gray cat, whereas if she was Dd, she would be black. In fact, I have a kitten she gave birth to who is black.... I know that that cat is Dd. (if she got a d from dad, she'd be gray, and she got a d from mom because that's all mom has to give.

Being gray makes her MORE likely to be killed by one of the great big hawks in my area....her phenotype, gray is acting against her. Her genotype causes the phenotype.

My black cat, who is Dd, is just as well hidden from the hawks as a black cat who is DD, because of that, we say that PHENOTYPE, rather than genotype is what selection acts on.

because a cat can carry the dilution gene (have the dilution genotype) without expressing the dilution phenotype (they have to have 2 copies of it to do so) their phenotype is what causes the difference in selection.

So natural selection acts on the phenotype (what is expressed) not the genotype (what genetics are inside the animal) because genotype that is not expressed as phenotype is not expressed, and not there to be worked on.

Answer 7

their is no geno types