Zebrafish Population Genetics Under Isolation
When a small population, like the isolated zebrafish described, experiences reduced population size and becomes isolated (preventing gene flow), specific evolutionary forces become more pronounced.
Impact of Small, Isolated Populations
- Genetic Drift: In small populations, random chance events have a significant impact on allele frequencies. This is known as genetic drift. Alleles can be lost or become fixed purely by chance, not necessarily because they are advantageous or disadvantageous.
- Isolation: The lack of gene flow from other populations means no new genetic variations can enter, and existing variations cannot easily spread. The population evolves based only on factors within the isolated group.
Consequence: Reduced Genetic Variability
The combined effects of strong genetic drift and lack of gene flow in a small, isolated population lead to a decrease in genetic variability. Over generations, some gene variants (alleles) are lost, and others may become universal (fixed), reducing the diversity of genetic traits within the population.
Analysis of Options
- Genetic variability is low: This is the most likely outcome due to strong genetic drift in a small, isolated population.
- Fixation of genotypes due to drift is low: Incorrect. Drift tends to increase fixation rates in small populations.
- Inbreeding is low: Incorrect. Small, isolated populations often experience increased inbreeding.
- Mutation rate is high: There is no evidence to suggest a change in the mutation rate; drift is the dominant factor affecting variability here.
Important Questions from Genetic drift
- Which one of the following statements about genetic drift is accurate?
- 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?
- 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).
