meiosis reduction division post falls high school science department
TRANSCRIPT
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MeiosisReduction Division
Post Falls High SchoolScience Department
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A. Sexual Reproduction
• 1. Asexual repro. needs only one parent
• 2. Sexual repro. needs two sex cells– a. Sperm--male sex cell– b. Egg--female sex cell
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B. Importance of Sex Cells• 1. In body cells, chromosomes
found in pairs– a. Pairs form because chromosomes
are alike– b. Cell with 2 of every kind of
chromosome is called diploid– c. Sex cell is haploid--23
chromosomes in egg or sperm
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B. Importance of Sex Cells
• 2. Sexual repro starts with sex cell & ends with fertilization– a. Zygote is formed in fertilization--in
humans it is diploid or 2n with 46 chromosomes
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Meiosis occurs in reproductive organs only; not in somatic (body)
cellsMeiosis is called “reduction
division” because the chromosome number is reduced to half the
normal number for that particular species; from “diploid” (46 in
humans) to “haploid” (23) in the gametes (sex cells)
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See Chapter 10 (Honors) or 11 (General Biology) to
discover the value, importance, and advantage organisms gain by meiosis and sexual reproduction
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C. Meiosis--Sex Cell Formation
• 1. In meiosis, there are 2 divisions of the nucleus: meiosis I & meiosis II
• 2. Prophase I: double stranded c’somes and spindle fibers appear; nuclear membrane and nucleolus fade
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• 3. Metaphase I: chromosome pairs (chromatids) line up– spindle fibers attach to centromeres
and centrioles
• 4. Anaphase I: chromotids separate from matching pair
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• 5. Telophase I: cytoplasm divides and 2 cells form
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• 6. Prophase II: chromatids and spindle fibers reappear but no duplication of chromatids occurs
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• 7. Metaphase II: chromatids line up in the center of the cell– spindle fibers attach to centromere &
centriole
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• 8. Anaphase II: centromere divides– chromosomes split and move to opposite
poles
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• 9. Telophase II: spindle fibers disappear– nuclear membrane forms around
chromosomes at each end of cell; cytokinesis occurs
– each nucleus has half the # of chromosomes as the original (haploid)
– now there are 4 sex cells (daughter cells)
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So, all meiosis occurs identically, right?
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Actually, it is different in the male and female
processes!
Check out the differences between spermatogenesis in males and oogenesis in
females
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Spermatogenesis
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Click below for an animation. Read the intro, view the
animation, read the conclusion, and take the quiz.
Meiosis
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Why does the meiotic process produce so many more spermatozoa than ova?
For a challenge, respond to the questions on the following site:
Some Questions for You