Explain why genetic variation within a population is a prere

Explain why genetic variation within a population is a prerequisite for evolution. What factors can produce genetic variation among populations? If a population stopped reproducing sexually (but still reproduced asexually), how would its genetic variation be affected overtime? Explain. Of all the mutations that occur in a population, why do only a small fraction become widespread among the population\'s members?

Solution

A-Within a population, genetic differences among individual provide the raw material on which natural selection and other mechanisms can act. Without theses type of differences allele frequencies would not change over time and hence population would not evolve. Genetic variation (the way genes vary across a species) causes natural selection. We can take the example of the Giraffes. Among the Giraffes most of them are long necked and some are short necked. The ones with long neck can reach upto the greater heights of the trees and hence can get food, while those with short neck cannot reach to the highest branch and eventually they die over the course of time due to lack of food. This is survival of the fittest. When the short nech giraffes die their progeny decreases and gradually all of them perish, while the long necked giraffes continue to live and reproduce and produce the young ones which have long necks.

B-Genetic variation among population can arise from Natural selection if slelection favours different alleles in different populations, this might occur for example, if the different populations experience different environmental conditions. Genetic variation also arises from Genetic Drift when the genetic difference between the populations are selectively neutral.

C-Its genetic variation (whether measured at the level of the gene or at the level of the nucleotide sequence) would probably drop over time. During meiosos, crossing over and independent assortment of chromosomes produce many different and new combinations of alleles. Further, any population contains a vast number of mating combinations and fertilization of gametes of individuals with different genetic background. Thus, via crossing over, independent assortment of alleles and fertilization, sexual reproduction reshuffled alleles into fresh combos each generation. If sexual reproduction is stopped and asexual reproduction continues then the new sources of genetic variation would be reduced and thus overall amount of genetic variation would drop.

D-The mutations of the somatic cells that do not produce gametes are lost when the organism dies. Of mutations that do occur in cell lines that produce gametes, amny do not have a phenotypic effect on which natural selection can act. Some others have a harmful effect and are thus unlikely to increase in frequency as they decrease the reproductive success of their bearers.