Question

What are the sources of genetic variation in sexually-reproducing organisms? In asexually-reproducing organisms, such as viruses and prokaryotes?

Answer 1

Sources of genetic variation in sexually-reproducing organisms

The sexually reproducing organisms will have variation through independent assortment, crossing over and random fertilization.

In case of independent assortment, the random orientation of tetrads which occur during the process of metaphase will generate the variation as each daughter cell during meiosis I will 50-50 chances to get maternal or paternal chromosome. So if you take in humans, the number of possible combination of chromosomes are 2²³ or 8 million.

During crossing over, the genes inherited from father and mother will combine to produce recombinant chromosomes. The crossing over is observed between homologous portions of two non-sister chromatids and through independent assortment, during meiosis II the non-identical sister chromatids will produce a variety of gametes with different genetic types of gametes.

Sources of genetic variation in asexually-reproducing organisms

If you see in asexual reproduction, here the offspring will be arising only from a single organism, so it will be inheriting the genes from a single parent. But still they will have genetic variation by undergoing mutations. Through mutations these asexually reproducing organisms will have a change to acquire new genetic information.

For example, through conjugation the bacteria will acquire genetic variation in its genome.