A really tough (for me) evolution question...

[kankerfist]

I just took a test that had a question that stumped me... I still can't figure out the answer:

Q: Evolution is a ____ over time

A) change in distribution of phenotypes in a population
B) change in distribution of genotypes in a population

I am under the impression that :
-natural selection is the process that acts directly on phenotypes in a population
-evolution is the result of natural selection over a long time
-a genotype can be identified by its phenotypes

Can someone help me figure out why one answer would be better than the other? Are my 3 assumptions correct? Any tips would be appreciated!

[canalon]

I would say B, because sometimes apparent change in phenotypes can happen without changes in genotype (Not very frequent though) so I tend to relate evolution to the "original cause" i.e the genotype. Yet I can understand that A could be a good answer too.

And yes your assumptions are correct As far as I know.

[AstusAleator]

Genotype, for the most part, determines phenotype. Thus, even though natural selection operates on phenotype, the result is a change in genotype.

The answer would be neither. Evolution is a change in the number/distribution of GENES over time. Often, shifts in genotypes will denote a shift in the number of genes, but not necessarily.

For example, you have a population with 50 rr and 50 RR fireflies where R is red eyes and r is white eyes. If having white eyes decreases fitness to a significant degree, you will see the population naturally shift towards more individuals with red eyes. So eventually you may have a population where there are 10 rr, 50 rR, and 40 RR.
Since R is dominant (signified by caps) then rR exhibits the phenotype of red eyes. Thus the population now has 10 white-eyed individuals and 90 red-eyed individuals.
If you count the occurences of genes, you'll see that there are less r and more R.
50rr and 50RR = 100r and 100RR
10rr 50rR and 40RR = 70r and 130R
Now, having more red eyes doesn't always necessarily mean that there are less r genes in the population (for example 20rr 60rR 20RR), but if that is the case then you have evolution.

So the take home point is that:
from an original population 50rr and 50RR
20rr 60rR 20RR is a shift in genotype but not genes.
10rr 50rR 40RR is a shift in genotype AND genes, and is thus evolution.

[/b]

[Locus]

Evolution is a change in the number/distribution of GENES over time.

Allels of the genes, not genes itself directly^ shimpanse and human has similal genes but different alleless that had changed during the evolution.

[clumpymold]

Evolution is a change in the number/distribution of GENES over time.

Allels of the genes, not genes itself directly^ shimpanse and human has similal genes but different alleless that had changed during the evolution.

Uh, pretty much what he said (I think). Evolution is the change in the frequency of alleles in a given gene pool of a population over time.

Nothing about genes or phenotypes there. Just alleles.

[Darby]

It's a flawed question, to be sure, but there is an answer.

Selection can only work on expressed alleles, so it's phenotypes. Phenotypes are related to genotypes, and the overall gene pool is affected as well, but the process deals with effects rather than hidden codes.

[Locus]

Uh, pretty much what he said (I think). Evolution is the change in the frequency of alleles in a given gene pool of a population over time.

Nothing about genes or phenotypes there. Just alleles.

Briliant definition of evolution!!! I fully agree!

[AstusAleator]

I stand corrected Alleles, not genes.

[AstusAleator]

It's a flawed question, to be sure, but there is an answer.

Selection can only work on expressed alleles, so it's phenotypes. Phenotypes are related to genotypes, and the overall gene pool is affected as well, but the process deals with effects rather than hidden codes.

Sorry to double post but...

Selection is not the only force of evolution. There is also genetic drift and gene flow (among others). These processes can both operate independently of phenotype (though gene flow may be effected in some way by it depending on the situation).

I maintain that the given answers are both false.

[45561]

Evolution is change between generations within a population, usually described as changes in allele frequency. I'd run with B.

[JDavidE]

I am already being pilloried so I'll do some stirring here as well. Were I to take that test (and I'm glad it was you) my answer would have been A. Phenotype. Go back to Darwin's finches. The genus didn't change, but the phenotypes did.

[AstusAleator]

Generally subspecies and species are subject to change before genus. Regardless, I'm sure the genotype DID change.