Ans.The main sources of variations in sexually reproducing populations are as follows;
• The genetic recombination produced through crossing over (recall that crossing over occurs during meiosis) results in gametes with variations.
• Mutations (changes in DNA) are important source of variations. Mutations also happen during gametes formation through meiosis.
• During fertilization, one of the millions of sperms combines with a single egg. The chance involved in this combination also act as the source of variations.
• Gene flow i.e. movement of genes from one population to another is also an important source of variations.
• Variations are also caused by different combination of chromosomes in gametes and then in zygote. In the case of humans possible number of chromosomal combinations at fertilization is 70,368,744,177 ,664. In other words, a couple can produce