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.
Correct Answer: DImportant Questions from Genetic drift
- Which one of the following statements about genetic drift is accurate?
- 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 In a population of birds on an island, the average beak size reduced over one generation. A researcher estimated the association between beak size and relative fitness, shown in the graph. The estimated slope was –0.05 with a 95% confidence interval of -0.15 to 0.09.
Which one of the following evolutionary processes acting on beak size is the most likely reason for the observed reduction in beak size?
- Two isolated populations X and Y have 100 and 10000 individuals, respectively. Both populations have the same starting allele frequencies of p=0.5 and q=0.5. After 1000 generations of genetic drift, which of the following statements is true about the heterozygosity at this locus in these two populations?
