Review:
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stages of mitosis
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cancer cells
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mitosis and cancer
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cancer treatments
Nov 3­1:04 PM
Meiosis:
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the division of cells to create the sex cells known as gametes (egg and sperm)
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involves the halving of genetic material (chromosomes)
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means an egg or sperm would have half the number of chromosomes
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human body cells have a diploid number of 46 chromosomes while sex cells have a haploid number of 23 chromosomes
Haploid(monoploid) cells contain half the number of chromosomes (n)
Diploid cells contain a full number of chromosomes (2n)
Ex. human body cells (2n) = 46 chromosomes
sperm cells (n) = 23 chromosomes
Nov 3­1:06 PM
1
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when fertilization occurs the chromosomes from the egg and sperm join to form a zygote
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in humans two haploid (n) gametes fuse to form a diploid (2n) cell
* 23 chromosomes + 23 chromosomes = 46
Nov 3­1:12 PM
Stages of Meiosis:
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as with mitosis the cells are in interphase before division occurs
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chromosomes will divide and double before meiosis begins
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meiosis has an extra sequence over mitosis
Mitosis: 46 interphase 92 mitosis 46 (2 cells)
Meiosis:46 interphase 92 meiosis 1 46 meiosis 2 23 (4 cells)
Nov 3­1:16 PM
2
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stages of meiosis are the same as mitosis but there are two sets of the four stages
Meiosis 1
Meiosis 2
prophase 1
metaphase 1
anaphase 1
telophase 1
prophase 2
metaphase 2
anaphase 2
telophase 2
* the events in each stage are similar to mitosis but the extra stage ensures half the number of chromosomes
* see handout provided (turn to diagram on page 472)
Nov 3­1:22 PM
Nov 3­1:31 PM
3
The Results of Meiosis
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when meiosis is complete there are four new haploid cells ­
in males all four cells survive to become sperm
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in females only the largest one cell survives to become the egg
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this is called gametogeneis of which there are two types:
(a) Spermatogenesis
(b) Oogenesis
(see handout provided)
Nov 3­1:31 PM
Spermatogenesis
Nov 3­6:58 PM
4
Oogenesis
Nov 3­6:58 PM
Readings:
­ pages 470 ­ 478
­ stem cell article on page 479
Questions:
­ page 480, #'s 1,2,3,4,5
Assignment:
STSE #2: Nov 3­7:00 PM
5