Genetic Variation in:
Independent Assortment of Chromosomes – Homologous pairs of chromosomes are randomly oriented
at metaphase of meiosis I. Each pair may orient such that either the paternal or maternal homolog are
closer to a given pole which gives a 50% chance that a daughter cell of meiosis I will get will get the
maternal chromosome and a 50% the daughter cell will get the paternal chromosome. Each homologous
pair of chromosomes is positioned independently of the other pairs. The number of possibilities in
humans by independent assortment in the gametes is 223.
Crossing Over – During prophase of meiosis I, a set of proteins cause an exchange of corresponding
segments of one maternal and one paternal chromatid. Through this exchange, end portions of
nonsister chromatids trade places to produce genetic variation. The resulting chromosomes are called
recombinant chromosomes, chromosomes carrying genes from two different parents. Crossing over is a
very important source of genetic variation and increases the number of genetic possibilities of daughter
cells resulting from meiosis astronomically.
Random Fertilization – The fusion of a male gamete with a female gamete will produce a zygote of 223 x
223 possibilities from independent assortment. If the genetic variation brought about crossing over is
factored in, the possibilities are astronomical.