Meiosis and Genetic Variation Biology 4th & 7th Hall ©Hall2010

Gene Variation There are 3 mechanisms that contribute to genetic variation in sexual organisms. Independent Assortment Crossing-Over Random Fertilization

Independent Assortment Each gamete receives one chromosome from each of 23 pairs of homologous chromosomes Which chromosome the gametes receive is up to chance There is random distribution during meiosis

Crossing-Over DNA exchange that occurs during crossing-over adds even more recombination to independent assortment Number of genetic combinations that can occur are almost unlimited

Random Fertilization Zygote is formed by random joining of 2 gametes 50 - 500 million sperm per ejaculation Typically one egg, although more than one is possible

Importance of Genetic Variation ESSENTIAL TO EVOLUTION Generates variation the quickest Pace of Evolution increases as the level of genetic variation increases Natural Selection does not always favor genetic or outward change.

Chick Variation