List the most likely force (or mechanism) resulting in the observed pattern or change to a population?

blue01

2010-06-07 6:25 am

List the most likely force (or mechanism) resulting in the observed pattern or change to a population

1) HIV patients treated with powerful anti-retroviral drugs initially show a decline in circulation viruses but then show a rapid increase despite continued treatment with the drugs.

2) The most successful swiss starlings have 4 or 5 eggs. Those that have fewer or more eggs, are less successful in raising the chicks.

3) Two cousins marry and one of their children suffers from a rare genetic disease.

回答 (1)

[匿名]

2010-06-07 7:52 am

✔ 最佳答案

1. Mutation and Natural selection
The viruses are initially affected by the drug, but some are not affected due to being genetically different from the main population due to some mutation or mutations. The drugs "kill" the nonresistant viruses, leaving only the resistant ones to reproduce (with the aid of host cells) and increase in number.

2. Stabilizing selection
Natural selection favors intermediate phenotypes and disfavors both extremes in phenotype (here, number of eggs laid). The mean in the phenotype is not changed, but the variance is reduced, resulting in a narrowing of the bell curve.

3. Inbreeding
Inbreeding involves mating between closely related individuals. It does not create mutations nor does it change allele frequencies, but it does alter genotype frequencies by increasing homozygosity, possibly at a large number of loci. Increased homozygosity increases the probability of offspring being homozygous for a deleterious recessive trait.

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