Question
A large proportion of individuals in a particular population of humans carry the allele for colour-blindness. Assuming colour-blindness does not confer any evolutionary advantage, which of the following mechanisms CANNOT explain the unusual abundance of this allele?
The correct answer is
Purifying selection
Examining Allele Frequency Mechanisms
The question asks to identify the mechanism that CANNOT explain why an allele for a disadvantageous trait, such as colour-blindness, is unusually abundant in a human population, given that the allele confers no evolutionary advantage.
- Founder effect: This can cause specific alleles, even rare or disadvantageous ones, to become common in a new population if the small group of founders happened to possess a high frequency of that allele.
- Genetic drift: Random chance events can cause allele frequencies to fluctuate, especially in smaller populations. This random fluctuation can lead to an increase in the frequency of a disadvantageous allele over time.
- Genetic hitchhiking: This occurs when an allele increases in frequency because it is located near a gene that is under positive selection. Even if the allele itself is neutral or slightly disadvantageous, it can increase in frequency if it's linked to a strongly favoured allele.
- Purifying selection: This is a form of natural selection that acts to eliminate deleterious alleles (harmful mutations) from a population. It works to decrease the frequency of disadvantageous alleles.
Purifying selection directly opposes the increase in frequency of disadvantageous alleles. Therefore, it cannot explain the unusual abundance of the colour-blindness allele.
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Important Questions from Genetic drift
- In a diploid population of N individuals, the probability of fixation of a new neutral mutation (assuming no other mutation occurs) is _________.
- Two isolated populations M and N have population sizes of 100 and 1000 individuals, respectively. The starting allele frequencies p and q are 0.5 in both populations. Assuming no selection, which one of the following is expected after 100 generations?
- A few years ago, a very small population of zebrafish became isolated by a newly built dam. As a result, which statement is most likely to be true about this population of zebrafish now?
- Which two of the following processes can result in a decline in heterozygosity in populations?
I) inbreeding; II) genetic drift; III) mutation; IV) random mating - Which of the following processes typically does NOT contribute to increase in genetic variation?
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