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MEIOSIS

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! Meiosis results in 4 genetically different cells! So genetically different offspring result!

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MEIOSIS

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  1. MEIOSIS Cell Division to form Gametes Animation

  2. Meiosis: Animation CLICK HERE!

  3. 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!

  4. 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)

  5. Vocabulary con’t…….. • Diploid (2N): • 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!

  6. DRAW CROSSING OVER!

  7. 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

  8. Gametogenesis

  9. KEYS TO MEIOSIS • Original cell has complete set of chromosomes (Diploid or 2N) • 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

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

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

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