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.
Sexual reproduction is a source of genetic variation. Recombination of chromosomes during meiosis allows for the exchange of DNA, also known as independent assortment. Random â¦segregation also plays a role, as well as some mutations to change the phenotype within different offspring.