Meiosis Division of Sex Cells Meiosis A process

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