Meiosis Division of Sex Cells

Meiosis A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Diploid – 2 sets of chromosomes Haploid – 1 set of chromosomes Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

Meiosis

Meiosis Stages Meiosis usually involves 2 distinct stages Meiosis I Meiosis II

Prophase I Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromosomes in a tetrad. The pairing of homologous chromosomes is the key to understanding meiosis. Crossing-over may occur here Crossing-over is when chromosomes overlap and exchange portions of their chromatids.

Prophase I

Metaphase I Spindle fibers attach to the chromosomes Tetrads attach

Metaphase I

Anaphase I The fibers pull the homologous chromosomes toward opposite ends of the cell. Tetrad splits apart into pairs.

Anaphase I

Telophase I & Cytokinesis Nuclear membranes reform. The cell divides into 2 cells.

Telophase I

Prophase II Meiosis I results in two diploid (2N) cells. Each cell has the same number of chromosomes as the original cell before replication. There is NO Interphase before!

Prophase II

Metaphase II The chromosomes line up similar to metaphase in mitosis.

Metaphase II

Anaphase II Sister chromatids separate and move to opposite ends of the cell.

Anaphase II

Telophase II Meiosis II results in 4 haploid cells.

Telophase II

Gamete Formation In males, meiosis results in 4 sperm cells In females, meiosis results in 1 egg cell and two polar bodies, which are not used in reproduction.

Mitosis vs Meiosis Mitosis Meiosis Results in 2 Diploid Cells (2N) 4 Haploid Cells (N) Cells are Genetically Identical Genetically Different Occurs in Somatic (Body) Cells Sex Cells