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
- 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?
- 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?
All else being equal, among isolated populations comprising of 10, 100, 500 and 1000 individuals, the impact of random genetic drift is LOWEST in the population with _____________ individuals.
