Great Migration: Life for Migrants in the City. By the end of 1919, some 1 million blacks had left the South, usually traveling by train, boat or bus; a smaller number had automobiles or even horse-drawn carts.
Genetic variation is increased by meiosis During fertilisation, 1 gamete from each parent combines to form a zygote. Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA.
Genetic variation is a change in the genes that occur in organisms in a population. This variation typically occurs through DNA mutation, gene flow (movement of genes from one population to another) and sexual reproduction.