Meiosis and Variation

Meiosis is the splitting of sex cells during sexual reproduction to pass on 23 chromosomes to the offspring.

]]MEIOSIS IS MITOSIS BUT FOR SEX CELLS (GAMETES)]]

Results in 4 daughter cells that are haploid and have novel chromatids due to crossing over.
  * Long explanation: One full diploid sex cell from each parent (one sperm, one egg) splits twice creating 4 new cells called daughter cells. This is done in three phases: interphase, meiosis one, and meiosis two.
    * In interphase, a diploid sex cell will $double its chromosomes$ from 46 to 92 in one cell. These new (novel) chromosomes are still the same as before just twice the number (homologous).
    * In meiosis one, the cell with 92 chromosomes will $split into two$ diploid daughter cells with non-homologous chromosomes.
    * In meiosis two, the two diploid daughter cells will $split again$ ending the entire cycle by creating 4 non-homologous haploid daughter cells ready to be merged with another haploid cell of a sperm or egg to create a diploid zygote.

The Three Methods for Genetic Variation

%%Independent Assortment%% - genes that do not reside on the same chromosome may sort independently (anaphase 1 of meiosis)

1. the formula for possible combinations is 2^n, where n = # of haploid chromosomes

%%Random Fertilization%% - only one sperm will fertilze the egg and turn the haploid into a diploid. It’s random which sperm will get there.

1. fertilization is the opposite process of meiosis

%%Crossing Over%% - genetic information may be exchanged between homologues, further shuffling the genetic information of the eventual gamete (prophase 1)

1. uses non-sister chromatids

These three process are found in all eukaryotes!