Four haploid Algae Cells MEIOSIS Four haploid Algae Cells

MEIOSIS “Cell Division which produces Gametes with half the number of chromosomes in the parent’s body.” In humans, Gametes are haploid cells with 23 homologous chromosomes in each. Meiosis takes place in the male and female reproductive organs. Male Gametes – Sperm Female Gametes - Eggs

Mitosis produced TWO new cells, while Meiosis produces FOUR new cells!

Do you remember Mitosis? Mitosis – “Cell Division” Results in 2 copies of the Original cell. Why do cells Divide? Grow Old Grow too Large

Compare Mitosis and Meiosis 4 HAPLOID CELLS! 2 DIPLOID CELLS!

Why MEIOSIS? 1. Diploid (2n) organisms must produce Haploid (n) cells before they can reproduce sexually. Sexual Reproduction guarantees a “mixing” of genes. This mixing of genes helps that species have enough variation to survive changing environmental conditions. MEIOSIS is the process of “mixing” those genes

MEIOSIS - Step 1 The number of chromosomes must be halved to form gametes. Diploid Cell (46 chrom.) -----> 4 Haploid Cells (23 chrom.) GAMETES

MEIOSIS - Step 2 Meiosis I: DNA replicates to form “homologous chromosomes.” 46 chrom. --> 92 total chrom. After the first cell division, each cell has one set of homologous chromosomes which have 2 copies of identical DNA Prophase I Telophase I http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/page3.html

MEIOSIS - Step 3 Metaphase I: “crossing over”. Genes mix by switching chromosomes Source of Genetic Variation, which is how organisms evolve

MEIOSIS - Step 4 Anaphase I: Chromosomes line up but don’t split around the centromeres. Instead, the entire chromosome moves apart.

MEIOSIS - Step 5 Telophase I: Results in two cells, each with 46 chromatids. Meiosis II begins AFTER Telophase I (the last step in Meiosis I)

MEIOSIS - Step 6 Meiosis II: the same process as mitosis, but without DNA replication. It’s called “reduction division.” 2 diploid cells (46 chrom) --> Cell Division

MEIOSIS - Step 7 Results in 4 haploid cells with 23 chromosomes in each. These cells are also called Gametes or daughter cells. http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/page3.html

Why Meiosis? What is this micrograph showing? Diploid (2n) organisms must produce Haploid (n) cells before they can reproduce sexually. Sexual Reproduction guarantees a “mixing” of genes. This mixing of genes helps that species have enough variation to survive changing environmental conditions. 4 MEIOSIS is the process of “mixing” those genes Pollen grains being produced by Meiosis in a Lilly plant