Meiosis Chapter 11 Sec. 4

Meiosis Reduces # of chromosomes to half Diploid (2n) to haploid (1n)

Meiosis Produces gametes = sperm and egg Each contains 23 chromosomes

Stages of Meiosis Goes through G1, S, G2 Basically go through mitosis twice 1 cell divides into 4 cells with half of information

Meiosis I Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 and cytokinesis 1

Prophase 1 DNA coils into chromosomes Spindle fibers appear Nuclear envelope disappears

Prophase 1 Homologous pairs form tetrads Crossing over can occur here –Exchange of genetic material between chromosomes

Prophase 1 Crossing over results in genetic recombination –Produces new genes

Metaphase 1 Tetrads line up along the equator of cell Kinetochore attach to centromeres

Anaphase 1 Kinetochore pulls tetrads apart to separate poles Randomly separates= independent assortment Provides variation

Telophase 1 Chromosomes reach separate ends Cytokinesis begins

Meiosis 1 Original cell produces two new cells Each contains one chromosome= haploid

Meiosis 2 Second stage of meiosis –Prophase 2 –Metaphase 2 –Anaphase 2 –Telophase 2 and Cytokinesis

Prophase 2 Spindle fibers form Nuclear envelope disappears

Metaphase 2 Chromosomes move to middle of cell

Anaphase 2 The chromatids separate and move towards opposite poles

Telophase 2 Nuclear membrane forms Cytokinesis occurs Results in 4 new cells each with haploid #

meiosis

Gametes In animals meiosis = gametes Occurs in testes and ovaries Only in sex chromosomes

Spermatogenesis Production of sperm cells

Oogenesis Production of eggs

Asexual Reproduction Production of offspring from one parent –Mitosis, binary fission or budding –Genetically identical

Sexual Reproduction Production of offspring through meiosis and union of sperm and egg –Genetically different from parents