Evolution question multiple choices

[299678]

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1. There are 40 individuals in population 1, all of which have genotype A1A1, and there are 25 individuals in population 2, all of genotype A2A2. Assume that these populations are located far from one another and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is mostly likely an example of

genetic drift.
gene flow.
disruptive selection.
discrete variation.
directional selection.


2. A population of 15 birds inhabits a fairly new island. Ten of the birds are dark brown and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to _____.

natural selection
genetic drift
gene flow
disruptive selection
a cline

what do you think guys? I need a brief reasoning to support your answer

 

[TexasOMFS]

2. is genetic drift. None of the others fit. A cline is a difference in appearance due to different geography (both of these types of birds live on the same island so that's not it), disruptive selection is when extreme phenotypes are favored over intermediate ones, there's nothing stated in the problem to suggest that natural selection is taking place thus that cancels both A and D. Gene flow is due to migration of individuals out of or into a population (there's no migration). Genetic drift is changes in frequency due to random chance (note the problem states that they die by chance).

 

[TexasOMFS]

I believe 1 is discrete variation (i don't even know the definition of that, but the others don't fit by process of elimination).

 

[299678]

1. There are 40 individuals in population 1, all of which have genotype A1A1, and there are 25 individuals in population 2, all of genotype A2A2. Assume that these populations are located far from one another and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is mostly likely an example of

genetic drift.
gene flow.
disruptive selection.
discrete variation.
directional selection.


2. A population of 15 birds inhabits a fairly new island. Ten of the birds are dark brown and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to _____.

natural selection
genetic drift
gene flow
disruptive selection
a cline

what do you think guys? I need a brief reasoning to support your answer

answers for both of questions are genetic drift. I guess frequencies of alleles on both cases occur by random or chance. I hope someone can fully explain these questions

 

[orthosm2021]

agree with TexasOMFS with both answers.

regarding #1, it can only be either discrete variation or directional selection by process of elimination. I have no idea what discrete variation is but others dont really fit. Directional selection may work also if discrete selection is something totally random. It seems like only a specific genotype (homozygous) is favored in each population, which could a characteristic of directional selection (favoring extreme phenotypes).

 

[UCB05]

My first guess for #1 was disruptive selection.

The question mentions nothing to hint at gene flow or genetic drift. Discrete variation is the property whereby characteristics have discrete properties, e.g. black or white fur, attached or unattached ear lobes. The question doesn't mention anything about phenotype, so I would not go with this choice.

Directional selection favors one extreme over others, like long giraffe necks or male peacock flairs. Disruptive selection favors two extremes against a hybrid. The question mentioned that the two populations' environments are similar, and with the two populations representing full homozygous genotypes of one or the other, it seems that the environment encourages either but not hybrids, and not only one extreme (not directional) so I would go with disruptive selection.

A popular example of disruptive selection is black/white/gray rabbits hunted by wolves. Black rabbits hide around rocks, white rabbits hide around snow, gray ones get screwed. If you say that the black ones hide near some hilly rocks and white ones predominate 2 miles away in open fields and light brush, it would seem to fit the question very well

 

[299678]

1. There are 40 individuals in population 1, all of which have genotype A1A1, and there are 25 individuals in population 2, all of genotype A2A2. Assume that these populations are located far from one another and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is mostly likely an example of

genetic drift.
gene flow.
disruptive selection.
discrete variation.
directional selection.

The question ask for genetic variation, so we can eliminate directional, disruptive. Discrete variation occur within a population (purple flower or white flower within a same species), so we can eliminate it also. Question said similar environment, so the variation between two population appears to have resulted from chance events (drift) rather than natural selection. So correct answer is "genetic drift"


2. A population of 15 birds inhabits a fairly new island. Ten of the birds are dark brown and five of them are light brown. By chance, two of the dark brown birds and three of the light brown birds die before producing any offspring. All of the birds in the next generation are dark brown. This change in phenotypic frequency can be attributed to _____.

natural selection
genetic drift
gene flow
disruptive selection
a cline

This question gave us great hint, the question said, by chance, (ring a bell?)
Answer is genetic drift.

Final answers for both questions are genetic drift.