Meiosis and Variation

VERY GOOD YOUTUBE VIDEO: https://youtu.be/8yyxn0ERtBg

Basic Overview:

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

1. %%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

2. %%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

3. %%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!

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