MEIOSIS Cell Division to form Gametes Animation

Meiosis: Animation CLICK HERE!

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

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

Vocabulary con’t…….. Diploid (2N):Diploid (2N): –A cell that contains the full chromosome # I.e. mitosis always STARTS and RESULTS in a diploid number (46)I.e. mitosis always STARTS and RESULTS in a diploid number (46) I.e. meiosis always STARTS with diploid number (46)I.e. meiosis always STARTS with diploid number (46) Haploid (N):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 :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

KEYS TO MEIOSIS Original cell has complete set of chromosomes (Diploid or 2N)Original cell has complete set of chromosomes (Diploid or 2N) 2 divisions result in 4 DAUGHTER CELLS (gametes: 1 ova or 4 sperm)2 divisions result in 4 DAUGHTER CELLS (gametes: 1 ova or 4 sperm) –Genetic material is exchanged during CROSSING OVER CHROMOSOMES “criss-cross” EXCHANGING GENESCHROMOSOMES “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 chromosomesEx. If original cell has 46 chromosomes, gametes that result from meiosis will have 23 chromosomes OCCURS ONLY IN MULTICELLUAR, SEXUALLY REPRODUCING ORGANISMSOCCURS ONLY IN MULTICELLUAR, SEXUALLY REPRODUCING ORGANISMS

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

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