Phases of Meiosis

Figure 11-15 Meiosis Section 11-4 Meiosis I

Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

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 scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/ spindle fibers appear DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/ spindle fibers appear Homologous pairs match up

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 partner

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/ nucleolus return 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/ nucleolus disappear Centrioles/ 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

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

Ways Meiosis is different? Homologous pairs match up & trade DNA (SYNAPSIS & CROSSING OVER) in PROPHASE I SEGREGATION & INDEPENDENT ASSORTMENT in Anaphase I create genetic recombination Skipping INTERPHASE II- (Dividing TWICE but copying DNA once) produces 1n cells

Nondisjunction – Failure of homologous chromosomes OR chromatids to separate at anaphase

Mistakes in Meiosis Meiosis Lecture 4

Nondisjunction Results in ANEUPLOIDY = one or more chromosomes have extra or missing copies AFTER FERTILIZATION: Cell with only 1 copy of a chromosome instead of 2 = MONOSOMY Cell with 3 copies of a chromosome instead of 2 = TRISOMY

Errors in mitosis or meiosis can result in changes in phenotype Changes in chromosome number often result in: New phenotypes Sterility caused by triploidy and increased vigor of other polyploids human disorders with developmental limitations Trisomy 21 (Down syndrome) XO (Turner Syndrome)

Karyotype can show: Sex of baby Missing or extra chromosomes Major deletions or translocations Can’t see individual gene changes http://content.answers.com/main/content/wp/en/thumb/f/f3/220px-Down_syndrome_translocation.png

Down syndrome (Trisomy 21) Most common chromosomal abnormality (1 in 800 births) Similar facial features Slanted eyes / Protruding tongue Mild to severe mental retardation 50% have heart defects that need surgery to repair http://www.hadsa.org/ Both older (35+ years) and younger (under 16 years) mothers are more at risk. http://www.healthofchildren.com/images/gech_0001_0002_0_img0096.jpg

Some individuals with Down syndrome have the normal number of chromosomes but have all or part of a third chromosome 21 attached to another chromosome by translocation. http://content.answers.com/main/content/wp/en/thumb/f/f5/180px-Down_syndrome_translocation.png

Turner syndrome (X0) http://medgen.genetics.utah.edu/photographs/diseases/high/611.gif 1 in 5000 births Females have only one X chromosome Small size Broad chest Slightly decreased intelligence 35% have heart abnormalities Hearing loss common Reproductive organs don’t develop at puberty

http://www. akdeniz. edu http://www.akdeniz.edu.tr/tip/histoloji/embrders_dosyalar/slide0228_image1186.jpg Klinefelter syndrome 1 in 2000 births live births Males have extra X chromosomes (Can be XXy, XXXy, or XXXXy) Taller than average Normal intelligence have male sex organs, but are sterile. may be feminine characteristics, Often not discovered until puberty when don’t mature like peers Presence of BARR BODIES