Natural Selection, should be a more correct definition??

[pineappletree]

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The Kaplan book notes that "more favored genotypes are selected for"
But we all know that natural selection works at the phenotype level, not the genotype

Is this notable??


I ask in case a question like this comes on:

"Natural Selection selects for"
I.) Genotype
II.) Phenotype

a.) I
b.) II
c.) I and II

 

[illegallysmooth]

The Kaplan book notes that "more favored genotypes are selected for"
But we all know that natural selection works at the phenotype level, not the genotype

Is this notable??


I ask in case a question like this comes on:

"Natural Selection selects for"
I.) Genotype
II.) Phenotype

a.) I
b.) II
c.) I and II

This is not a big deal. Genotype causes phenotype. Natural selection selects based on ability to survive and produce viable offspring.

Edit: to be clear, I don't think this question would be asked. NS selects for genotype if the gene gives the organism increased fitness, which must happen via phenotype. If the genotype does not change the phenotype, it won't be selected for. So, NS selects for the genotype on the basis of the phenotype. This is a very roundabout circular question.

And to SU1989, even resistance to a pathogen would be characterized as phenotype. The phenotype is the physical manifestation of the genotype.

 

[unhappytnt]

I wondered the same thing when I was reading it. I would say it is both. Think of it this way: say a mutation causes one member of species to be resistant to a certain pathogen. This won't be apparent in the phenotype but yet still increase organism's chances of survival. So it's both the genotype and the phenotype.

 

[unhappytnt]

Having said that, I also agree with illegallysmooth: Genotype causes phenotype. So the answer would be genotype since it's more generalized.

 

[pineappletree]

Thank you!!!

 

[tncekm]

Kaplan is absolutely wrong in that case. Selection "for" is not driving evolution, it's selection "against" (i.e. the only way you can change the gene pool is when genes disappear, and that requires death and/or inability to reproduce sufficiently). And yes, it IS phenotype that is selected "against". It just so happens that certain genotypes are associated with phenotypes that are not "fittest". Keep in mind that genotype and environment can affect phenotype, so the outcome of natural selections will be different depending on environment.

However, don't think your MCAT will be this ambiguous (or wrong). Let it roll off of your shoulders and enjoy the fact that you're more well educated than the buffoon that wrote that question.

 

[startswithb]

Can't "selection for" and "selection against" both work? A mutation leading to an increased viability in an environment through better mating opportunities, etc., means the gene is more likely to continue OR a gene that leads to a decreased survival will cease to be passed on (if they die before reproductive opportunity)?

Kaplan is absolutely wrong in that case. Selection "for" is not driving evolution, it's selection "against" (i.e. the only way you can change the gene pool is when genes disappear, and that requires death and/or inability to reproduce sufficiently). And yes, it IS phenotype that is selected "against". It just so happens that certain genotypes are associated with phenotypes that are not "fittest". Keep in mind that genotype and environment can affect phenotype, so the outcome of natural selections will be different depending on environment.

However, don't think your MCAT will be this ambiguous (or wrong). Let it roll off of your shoulders and enjoy the fact that you're more well educated than the buffoon that wrote that question.

 

[pineappletree]

Thanks everyone~~
I suppose that these questions can easily be solved through deduction




Another question though...


Variation in Hardy-Weinberg equation signifies evolution is occurring. But can you know if random mating is specifically occurring?
I first thought no... that it can be any factor~~
But a question on the EK 1001 is challenging me...

 

[Lokhtar]

You mean how do you know if mating is completely random? The answer is that it almost never is. You'd have to study the behavior of the organisms in question to get more specific and/or to track the distribution of alleles.

 

[pineappletree]

Yes I know that equilibrium conditions are quite impossible, however it is for this question:


"Recently obtained data, on a population of Brazilian white squirrels, demonstrated a significant deviation from the expected data based on mating patterns between Ww x ww mammals. Based on this information it can be assumed that:

A.) Random mating was occurring in Brazilian white squirrels
B.) Random mating was not occurring in Brazilian white squirrels
C.) Random mating may be occurring in Brazilian white squirrels but data on a WW x WW cross is needed to confirm
D.) Random mating patterns in Brazilian white squirrels cannot be predicted based on the information provided



Basically the passage was talking about the Hardy-Weinberg equation the entire way through.
I thought that the answer was D because the variations could be due to anything like genetic drift...

The answer is B

 

[Lokhtar]

The answer can't be D though because if it was random, you could predict it (e.g, it would follow the HW equation). Meaning, if it was random, you would not need any more information to predict the outcome.

That's a great question. Half the Bio questions on my actual MCAT were like that 😡.

 

[pineappletree]

According to the question, couldn't it be either

-----> no Random mating
-----> Random mating + Genetic drift??



If either one is possible, the answer must be D...

 

[Phantastic]

...demonstrated a significant deviation from the expected data based on mating patterns between Ww x ww mammals...

They specifically tell you here the deviation is due to mating patterns between the heterozygote and homozygote. This indicates Nonrandom mating, and B states that the mating was not random.

Try not to introduce information. You need to assume the best answer is based only on the information given.

 

[tncekm]

Can't "selection for" and "selection against" both work? A mutation leading to an increased viability in an environment through better mating opportunities, etc., means the gene is more likely to continue OR a gene that leads to a decreased survival will cease to be passed on (if they die before reproductive opportunity)?

Well, you're thinking in the right direction in terms of understanding evolution, but is that selected for or just not selected against? I know that sounds like semantics, and sometimes the term "select for" is used in discussing evolution, but the reality is all organisms are pressured by mother nature, not nurtured by her. So, some species are more "selected against" than others, but none of them is prioritized, or "selected for", they simply experience less selective pressure.

 

[startswithb]

Well, you're thinking in the right direction in terms of understanding evolution, but is that selected for or just not selected against? I know that sounds like semantics, and sometimes the term "select for" is used in discussing evolution, but the reality is all organisms are pressured by mother nature, not nurtured by her. So, some species are more "selected against" than others, but none of them is prioritized, or "selected for", they simply experience less selective pressure.

I get what you're saying, now. I've never had it explained to me in that way. Thanks!