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![Page 1: A special type of cell division. Only occurs in reproductive organs Reduces the number of chromosomes in the nucleus -Reduction division.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551b3e03550346dd1a8b5522/html5/thumbnails/1.jpg)
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A special type of cell division.Only occurs in reproductive
organsReduces the number of
chromosomes in the nucleus -Reduction division
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End result: - Gametes in animals - Spores in plants
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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
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A.K.A. gametesContain half of the total
number of chromosomes Hap/oid number (n) Humans have a haploid
number of 23
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![Page 8: A special type of cell division. Only occurs in reproductive organs Reduces the number of chromosomes in the nucleus -Reduction division.](https://reader035.fdocuments.in/reader035/viewer/2022070307/551b3e03550346dd1a8b5522/html5/thumbnails/8.jpg)
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Example: Humans
Diploid =46 Haploid = 23
Female gamete = egg = n = 23 Male gamete = sperm = n = 23
Zygote (fertilized egg) = 2n = 46
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meiosismeiosis
mitosis
mitosis
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Each diploid cell has two copies of each chromosome
One copy 'donated' by the haploid egg
One copy 'donated' by the haploid sperm
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Homologous Chromosomes
Matching chromosomes
Carry information for the same genes
Tetrad
Two homologous chromosomes attached
•Tetrad:- Two homologous chromosomes attached
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Divided into two parts: Meiosis I & Meiosis II
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DNA replication
Homologous chromosomes form
Homologous chromosomes align at equator and separate into chromosomes
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Chromosomes align at equator and separate into sister chromatids
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GametogenesisDevelopment of gametes Occurs in organs (gonads)
of reproductive system Ovaries Testicles
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Oogenesis-In females - Produce eggs (ovum/ova)
Spermatogenesis.-In males - Produce sperm
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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.
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2. Crossover (Recombination) Totally Random and mistakes can occur
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3. Random Line up During Metaphase I
We have pairs of 23 so 223 = 8.4 million combinations
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4. Random Seperation During Metaphase II and Anaphase II