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 A special type of cell division.  Only occurs in reproductive organs  Reduces the number of chromosomes in the nucleus -Reduction division.

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Presentation on theme: " A special type of cell division.  Only occurs in reproductive organs  Reduces the number of chromosomes in the nucleus -Reduction division."— Presentation transcript:

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2  A special type of cell division.  Only occurs in reproductive organs  Reduces the number of chromosomes in the nucleus -Reduction division

3  End result:  - Gametes in animals  - Spores in plants

4  A.K.A. somatic cells  Contain the total number of chromosomes in an organism  Diploid number (2n)  Humans have a diploid number of 46 chromosomes

5  A.K.A. gametes  Contain half of the total number of chromosomes  Hap/oid number (n)  Humans have a haploid number of 23

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9  Example: Humans  Diploid =46 Haploid = 23  Female gamete = egg = n = 23 Male gamete = sperm = n = 23  Zygote (fertilized egg) = 2n = 46

10 meiosis mitosis

11  Each diploid cell has two copies of each chromosome  One copy 'donated' by the haploid egg  One copy 'donated' by the haploid sperm

12 HOMOLOGOUS CHROMOSOMES  Matching chromosomes  Carry information for the same genes TETRAD  Two homologous chromosomes attached Tetrad: - Two homologous chromosomes attached

13 Divided into two parts: Meiosis I & Meiosis II

14 DNA replication Homologous chromosomes form Homologous chromosomes align at equator and separate into chromosomes

15 Chromosomes align at equator and separate into sister chromatids

16

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18  Gametogenesis  Development of gametes  Occurs in organs (gonads) of reproductive system  Ovaries  Testicles

19  Oogenesis -In females - Produce eggs (ovum/ova)  Spermatogenesis. -In males - Produce sperm

20 1. Random Fertilization (not part of meiosis) - - picking a random mate - - determines which sperm fertilizes which egg Average number of sperm cells in the ejaculate of a healthy man: 200 and 500 million - an estimated 400,000 to 450,000 immature eggs residing in each ovary at puberty. - Any sperm can fertilize any egg. - The resulting zygote could contain anyone of more than 70 trillion possible combinations of chromosomes.

21 2. Crossover (Recombination) Totally Random and mistakes can occur

22 3. Random Line up During Metaphase I We have pairs of 23 so 2 23 = 8.4 million combinations

23 4. Random Seperation During Metaphase II and Anaphase II


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