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.
Random assortment of chromosomes produces many variations among daughter cells, giving rise to genetic diversity in offspring. A cell with 2 pairs of chromosomes gives 4 possible chromosome combinations in daughter cells (2^2).here are three mechanisms responsible for this: random assortment of chromosomes (chromosomes are sorted into daughter cells randomly), crossing over (chromosomes switch chunks of DNA) and random fertilization (chance alone is responsible for which sperm meets which egg).