MEIOSIS NOTES (11.4)

(Meiosis Notes 11.4) Reproduction Asexual- all of the parent DNA goes to offspring (miTosis-mainTains) Sexual -used to create sex cells(mEiosis-rEduce)

2 TYPES OF CELLS BODY CELLS SEX CELLS

-Also called somatic cells -Made by mitosis Body Cells -All cells other than sex cells -Also called somatic cells -Made by mitosis This scanning electron micrograph (courtesy of Dr. Marion J. Barnhart) shows the characteristic biconcave shape of red blood cells.

-Contain 2 copies of each chromosome -homologous chromosomes Body Cells -Contain 2 copies of each chromosome -homologous chromosomes -have diploid #, 2n EX. Humans =46

-Eggs and sperm -Made by meiosis -Have haploid #, n -EX. Humans =23 Sex Cells -Gametes -Eggs and sperm -Made by meiosis -Have haploid #, n -EX. Humans =23

How do we get 46 Chromosomes? Egg (haploid #) + Sperm(haploid #) ZYGOTE (diploid #) Ex. Humans 23 + 23 =46

-starts with 1 diploid cell and ends up with 4 haploid cells Meiosis  sex cells mEiosis = rEduction division -starts with 1 diploid cell and ends up with 4 haploid cells **Meiosis I and Meiosis II

Meiosis I

MEIOSIS II

Meiosis Diagram

ADVANTAGE: genetic variation CROSSING OVER Occurs during Prophase I of meiosis Tetrads form and DNA is exchanged XX ADVANTAGE: genetic variation

                                                               Adapted from: Morgan T.H., Sturtevant A.H., Muller H.J., and Bridges C.B., "The Mechansim of Mendelian Heredity", 1915. Crossing Over

Egg Formation (unequal cytokinesis)

Comparing Mitosis and Meiosis HOW MANY CELLS ARE MADE? Mitosis 2 Meiosis 4

Comparing Mitosis and Meiosis ARE RESULTING CELLS GENETICALLY THE SAME OR DIFFERENT? Mitosis- Genetically the same Meiosis - Genetically different

Comparing Mitosis and Meiosis WHAT TYPES OF CELLS RESULT IN THE PROCESS? (BODY CELLS OR GAMETES) Mitosis = Body cells Meiosis = Gametes

Comparing Mitosis and Meiosis WHAT ARE THE ADVANTAGES OF EACH PROCESS? Mitosis- Growth and repair Meiosis- Formation of sex cells and genetic variation