MEIOSIS Cell Division to form Gametes Meiosis Animation

MEIOSIS Cell Division to form Gametes

Meiosis: Animation CLICK HERE!

Things to remember • Genes from both parents are both in sex cells until meiosis occurs! • Meiosis results in 4 genetically different cells! So genetically different offspring result! • Half of genetic info from each parent! • The process is similar to mitosis, with a few VERY IMPORTANT NEW STEPS!

Vocabulary • Homologous Chromosomes: – Chromosomes from female parent that correspond to chromosomes from male parent. • Ex. 2 genes for eye color – 1 gene from mom (on chromosome z) – 1 gene from dad (on chromosome z)

Vocabulary con’t……. . • Diploid (2 N): – A cell that contains the full chromosome # • I. e. mitosis always STARTS and RESULTS in a diploid number (46) • I. e. meiosis always STARTS with diploid number (46) • Haploid (N): – A cell (always a gamete) that contains ½ the number of chromosomes – Meiosis results in cells with ½ number of chromosomes (23)! • Crossing-over: – Process when homologous chromosomes “cross” each other and exchange genes – Reason why you aren’t exactly like your siblings!

DRAW CROSSING OVER!

Spermatogenesis and Oogenesis • Spermatogenesis: – Formation of sperm cells – Results in 4 functional gametes • Oogenesis: – Formation of egg cells (ova) – Results in 1 functional gamete and 3 polar bodies

Gametogenesis

Basic diagram of Meiosis- Sperm 46 chromosomes Male Human Pre. Gamete Replication and Crossing-Over 46 different chromosomes 23 23 46 First cell division different chromosomes 4 functional sperm After 2 nd cell division 23 23

Basic diagram of Meiosis- Ova 46 chromosomes Female Human Pre. Gamete Replication and Crossing-Over 46 different chromosomes First cell division 1 functional ovum and 3 23 polar bodies 46 different chromosomes

Meiosis I • Interphase I – DNA copies itself • Prophase I – Chromosomes pair with their homologous partner to form a tetrad (4 chromatids) – CROSSING OVER OCCURS!!!!!!!

Meiosis I • Metaphase I – Homologous chromosomes align along middle of cell

Meiosis I • Anaphase I – Spindle fibers pull homologous chromosomes toward opposite poles

Meiosis I • Telophase I and Cytokinesis – Nuclear membranes reform – Cell separates into 2 cells

Meiosis II • Each cell still has 2 chromatids • The goal of meiosis II is to get 1 chromatid into each cell! • Prophase II – Happens very quickly – Spindle fibers appear – Nuclear membranes disappear

Meiosis II • Metaphase II – Chromatids align at middle of cells

Meiosis II • Anaphase II – Sister chromatids separate and move toward poles

Meiosis II • Telophase II and Cytokinesis – Chromatids are at opposite poles – Nuclear membranes reappear – Cells divide and result in 4 genetically different gametes that are HAPLOID!

Meiosis Square Dance link Start at 1: 35

KEYS TO MEIOSIS • Original cell has complete set of chromosomes (Diploid or 2 N) • 2 divisions result in 4 DAUGHTER CELLS (gametes: 1 ova or 4 sperm) – Genetic material is exchanged during CROSSING OVER • CHROMOSOMES “criss-cross” EXCHANGING GENES – Daughter cells (gametes) are genetically different – Daughter cells (gametes) are now HAPLOID or N ( ½ the original # ) • Ex. If original cell has 46 chromosomes, gametes that result from meiosis will have 23 chromosomes • OCCURS ONLY IN MULTICELLUAR, SEXUALLY REPRODUCING ORGANISMS

Basic diagram of Meiosis- Sperm 46 chromosomes Male Human Pre. Gamete Replication and Crossing-Over 46 different chromosomes 23 23 46 First cell division different chromosomes 4 functional sperm After 2 nd cell division 23 23

Basic diagram of Meiosis- Ova 46 chromosomes Female Human Pre. Gamete Replication and Crossing-Over 46 different chromosomes First cell division 1 functional ovum and 3 23 polar bodies 46 different chromosomes

Meiosis/Sexual Reproduction • Multicelluar-human, animal, flowering plants, trees • Two cell divisions • 4 daughter cells • Haploid (monoploid) (N) = ½ the number of chromosomes • Egg, sperm, pollen • Genetically different (VARIATION!!!!) • Diploid reduced to haploid • BEFORE zygote • BEFORE fertilization • NO PAIRS of chromosomes • Crossing-Over- the exchange of genetic material

Meiosis and Sexual Reproduction • Sperm and egg-ovumova (gamete) • Genetically different (VARIATION!!!) • Crossing-over (the exchange of genetic material) • Results in ½ haploid (monoploid) number of chromosomes • 4 daughter cells • NO PAIRS of chromosomes • BEFORE ferilization • BEFORE zygote • Multicellular-human, animal, flowering plants and trees • Reduced number

Meiosis/Sexual Reproduction • Genetically different (VARIATION)!!!!! • BEFORE fertilzation • 2 cell divisions • 4 daughter cells • Gametes (sex cells) • Egg and sperm (pollen) • CROSSING OVER (exchange of genetic materal) • Ovaries and testes • ½ # of chromosomes (haploid or monoploid) result • Reduced # of chromosomes • NO PAIRS of chromos in gametes!!!! • Multicellular- humans, animals, flowering plants, trees • BEFORE zygote

Words associated with Meiosis/Sexual Reproduction • Diploid (2 N) becomes haploid (N) (monoploid) • 2 cell divisions • Multicellular • Sexually reproducing. Corn, flowering plants, humans, other animals • Crossing Over- exchange of genetic material • Gametes (sex cells) • NO PAIRS IN GAMETES! • 4 daughter cells • VARIATION!!!!! • BEFORE fertilization • Making sperm and eggs • Two parents • Ovaries • Testes

Comparing Mitosis and Meiosis - Basic Diagram Animation

Comparing Mitosis and Meiosis - Diagram