Molecular exam question 7

Describe how unequal crossing over affects the amount of genomic DNA

Unequal crossing over occurs when homologous chromosomes misalign during meiosis and exchange DNA at non-equivalent positions. This can produce a duplication of a DNA segment in one chromosome and a deletion of that segment in the other. In turn, unequal crossing over can increase or decrease the amount of genomic DNA and generate variation in genome size within a population

Assuming that unequal crossing over is the only source of variation, describe what you would expect for the evolution of genomes by genetic drift in recently diverged populations.

Assuming that unequal crossing over is the only source of variation, genetic drift can randomly change the frequencies of these DNA duplications and deletions over time. Variants may increase or decrease in frequency by chance and may eventually become fixed or lost from the population. In recently diverged populations, there has been relatively little time for these variants to arise and for genetic drift to produce independent changes. Therefore, we would generally expect these populations to have relatively similar genome sizes

What would you expect for sister-species that have been evolving independently for a long time in terms of amount of genomic dna

Sister species that have evolved independently for longer have had more time for unequal crossing over events to generate different DNA duplications and deletions in each lineage. Genetic drift then acts independently in each species, potentially causing different variants to become fixed or lost. Over time, these independent changes can accumulate so we would generally expect the sister species to exhibit greater differences in genome size.

What would the extent of the differences between sister species genomes that hvae had al ong time to evolve independently depend on

The rate of unequal crossing-over determines how often new duplications and deletions arise while effective population size influences how strongly chance affects whether those variants persist, become fixed, or disappear.