MEIOSIS Chapter 11-4 Making reproductive cells …. called the gametes http://waynesword.palomar.edu/lmexer2a.htm Making reproductive cells …. called the gametes

+ EGG SPERM  If egg and sperm had same number of http://www.angelbabygifts.com/ Image by Riedell Image by Riedell EGG + SPERM  If egg and sperm had same number of chromosomes as other body cells . . . baby would have too many chromosomes! http://www.acmecompany.com/stock_thumbnails/13217.forty-six_chromosomes.jpg

is a special type of cell division… - makes cells with half number of chromosomes for sexual reproduction http://waynesword.palomar.edu/lmexer2a.htm

A. DIPLOID & HAPLOID -called homologous chromosomes - most cells have 2 copies of each chromosome = diploid (2n) (one from mom; one from dad) - all body or somatic cells are diploid. -called homologous chromosomes

- some cells have only one copy of each chromosome = haploid (1n) - all sperm and egg cells are haploid.

B. MEIOSIS Makes 4 cells genetically different from parent cell Makes haploid gamete cells Main cause of genetic variation in individuals reshuffles genes during process Used for sexual reproduction http://waynesword.palomar.edu/lmexer2a.htm

MITOSIS vs MEIOSIS INTERPHASE INTERPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html DNA is spread out as chromatin Nuclear membrane/ nucleolus visible DNA is copied during S phase Makes ‘stuff’ new cell needs in G2 SAME AS MITOSIS

MITOSIS vs MEIOSIS PROPHASE PROPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html DNA coils into chromosomes Nuclear membrane disappear Spindle fibers appear DNA coils into chromosomes Nuclear membrane disappear Spindle fibers appear Homologous chromosomes pair up

C. WHAT MAKES PROPHASE IN MITOSIS DIFFERENT FROM PROPHASE 1 IN MEIOSIS? -Exchange of DNA between homologous pairs = CROSSING-OVER during PROPHASE I -allows shuffling of the genetic material of DNA -creates genetic variation http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

SEE CROSSING OVER ANIMATION Video 5 Crossing Over SEE CROSSING OVER ANIMATION Video 5

MITOSIS vs MEIOSIS METAPHASE METAPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html Chromosomes line up in middle Chromosomes line up in middle with homologous pair

MITOSIS vs MEIOSIS ANAPHASE ANAPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html APART: APART: Chromatids split Chromatids stay together; Homologous pairs split

MITOSIS vs MEIOSIS TELOPHASE TELOPHASE I http://www.pbs.org/wgbh/nova/baby/divi_flash.html See TWO nuclei Nuclear membrane returns DNA spreads out as chromatin Spindle/centrioles disappear SAME AS MITOSIS

MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS I http://www.pbs.org/wgbh/nova/baby/divi_flash.html Cytoplasm splits into 2 cells SAME AS MITOSIS

MITOSIS vs MEIOSIS INTERPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html DNA is spread out as chromatin Nuclear membrane/ nucleolus visible DNA is copied during S phase SKIP INTERPHASE II DNA NOT COPIED

MITOSIS vs MEIOSIS PROPHASE PROPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html DNA scrunches into chromosomes Nuclear membrane disappear Spindle fibers appear SAME AS MITOSIS

MITOSIS vs MEIOSIS METAPHASE METAPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html Chromosomes line up in middle SAME AS MITOSIS

MITOSIS vs MEIOSIS ANAPHASE ANAPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html Chromatids split and move apart SAME AS MITOSIS

MITOSIS vs MEIOSIS TELOPHASE TELOPHASE II http://www.pbs.org/wgbh/nova/baby/divi_flash.html Two nuclei Nuclear membrane/ nucleolus returns Centrioles/spindle fibers disappear DNA spreads out as chromatin SAME AS MITOSIS Cells contain single copy of each gene

MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS II http://www.pbs.org/wgbh/nova/baby/divi_flash.html Produces 4 haploid cells, results in egg or sperm cells Cytoplasm splits, producing 2 diploid cells http://www.pbs.org/wgbh/nova/baby/divi_flash.html