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.
Independent assortment is a basic principle of genetics developed by a monk named Gregor Mendel in the 1860's. Mendel formulated this principle after discovering another principle now known as Mendel's law of segregation. This principle states that the alleles for a trait separate when gametes are formed.