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Meiosis and Sexual Reproduction

Honors Bio Presentation. Images from Biology: Life on Earth, 8th edition and Campbell Biology 7th edition.

Christopher Himmelheber

on 27 January 2014

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Transcript of Meiosis and Sexual Reproduction

Meiosis I
Meiosis II
Meiosis and Sexual Reproduction
Why do cells need meiosis?
Diploid number (2n) must be maintained after fertilization

If gametes were not haploid, chromosome number would double each generation

Meiosis is a reductive division
Different Organisms ... Different Sexual Lifecycles
Organsisms use a combination of mitosis and meiosis throughtout their lifecycle

Either the haploid or the diploid state (or both) can be multicellular
Chromosome Review
Errors in Meiosis
No DNA Replication
Reduction division
Forms two haploid cells
During anaphase
Chromosomes occur in homologous pairs

One from each parent

Diploid cells: 2 copies of each (2n)

Haploid cells: 1 copy of each (n)

Homologous chromosomes have same genes, but not neccessarily the same DNA sequences
During S phase, DNA replicates

Sister chromatids are exact copies of each other
Key Events of Prophase I
Homologous chromosomes pair up to form a tetrad
Crossing over
A nondisjunction occurs when chromosomes or sister chromatids fail to separate

Usually diagnosed via karyotype
Nondisjunction of sex chromosomes (X & Y)
Trisomy 21 = Down Syndrome
Trisomy 13 = Patau Syndrome
Trisomy 18 = Edwards Syndrome
Nondisjunction of somatic chromosomes (Pairs 1 - 22)
Big Questions
Why do cells need two types of cell division?

How is meiosis similar to mitosis?

How is meiosis different from mitosis?

What effects do errors during meiosis have on the individual?
Sources of Genetic Diversity
Independent Assortment
Crossing Over
For cells with a hapliod number n

Possible combinations = 2
Occurs at random locations

Functionally infinite possibilities
Key Points
Meiosis is a key part of sexual reproduction

Meiosis results in haploid daughter cells

Crossing over and random assortment lead to genetic diversity

Errors in meiosis result in changes in chromosome number
Sexual Reproduction = Genetic Diversity
Very similar to mitosis
Forms four haploid cells
Example: A cell with 6 chromosomes (n=3)

2 possible combinations = 8 genetically unique gametes
Full transcript