I) inbreeding; II) genetic drift; III) mutation; IV) random mating
Processes Causing Heterozygosity Decline
A decline in heterozygosity means that the proportion of heterozygous individuals in a population decreases. This occurs when populations tend towards homozygosity. Let's analyze the given processes:
- I) Inbreeding: This process involves mating between closely related individuals. It increases the likelihood that offspring inherit identical alleles from both parents (identical by descent), thus increasing homozygosity and reducing heterozygosity.
- II) Genetic Drift: This refers to random fluctuations in allele frequencies, especially significant in small populations. Over time, drift can lead to the loss of alleles or the fixation of others, which reduces the overall genetic variation and heterozygosity.
- III) Mutation: Mutations introduce new genetic variations by creating new alleles. While the immediate effect might be small, mutations generally increase or maintain genetic diversity, not decrease heterozygosity.
- IV) Random Mating: In a population where mating occurs randomly, allele and genotype frequencies remain stable (assuming other Hardy-Weinberg conditions are met). Random mating itself does not drive a decline in heterozygosity.
Identifying Key Processes
Based on the analysis, the processes that directly result in a decline in heterozygosity are inbreeding and genetic drift.
- Inbreeding specifically promotes homozygosity.
- Genetic drift, through random chance, can lead to loss of alleles and reduced heterozygosity, particularly in finite populations.
Therefore, processes I and II are the correct choices.
Important 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?
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?
- In a population of 100 individuals of a diploid organism with 1:1 sex ratio, the probability of fixation of a new neutral mutation is ______ (round off to three decimal places).
