Meiosis

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Meiosis A Source of Distinction
Why do you share some but not all characters of
each parent?
What are the rules of this sharing game?
At one level, the answers lie in meiosis.
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Meiosis A Source of Distinction
Meiosis does two things -
1) Meiosis takes a cell with two copies of every
chromosome (diploid) and makes cells with a
single copy of every chromosome (haploid).
This is a good idea if youre going to combine
two cells to make a new organism. This trick is
accomplished by halving chromosome number.
In meiosis, one diploid cells produces four
haploid cells.
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Reduction of Chromosome Number in the First
Division of Meiosis
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Meiosis A Source of Distinction
The second accomplishment of meiosis
2) Meiosis scrambles the specific forms of each
gene that each sex cell (egg or sperm) receives.
This makes for a lot of genetic diversity. This
trick is accomplished through independent
assortment and crossing-over.
Genetic diversity is important for the evolution
of populations and species.
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Keys to Understanding Meiosis
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One Way Meiosis Makes Lots of Different Sex Cells
(Gametes) Independent Assortment
Independent assortment produces 2n distinct
gametes, where n the number of unique
chromosomes.
In humans, n 23 and 223 8,000,0000.
Thats a lot of diversity by this mechanism alone.
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Another Way Meiosis Makes Lots of Different Sex
Cells Crossing-Over
Crossing-over multiplies the already huge number
of different gamete types produced by independent
assortment.
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Between Independent Assortment and Crossing-Over,
No Two Gametes Are Identical.
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Meiosis Following a Single Chromosome Pair
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The Key Difference Between Mitosis and Meiosis is
the Way Chromosomes Uniquely Pair and Align in
Meiosis
Mitosis
The first (and distinguishing) division of meiosis
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Boy or Girl? The Y Chromosome Decides
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Boy or Girl? The Y Chromosome Decides
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Oogenesis A Path of Meiosis in Humans
Woman are less busy in meiosis than men meiosis
produces only a few hundred mature eggs over a
lifetime.
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Spermatogenesis Another Path of Meiosis in
Humans
Men are busy meiosis produces roughly
250,000,000 sperm per day.
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Putting It All Together - Fertilization
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What Meiosis is About
Meiosis allows the creation of unique individuals
through sexual reproduction.