Bio 115 Cells & Evolution of Life
Genetics and Reproduction
Meiosis
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Bio 115 Cells & Evolution of Life
Evolution and Cell Division
Mitosis
Mitosis results in 2
genetically identical
daughter cells.
Important in
-growth
-asexual reproduction
Drawback: lack of genetic variation
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Bio 115 Cells & Evolution of Life
Meiosis vs. Mitosis
Meiosis
vs.
Mitosis
Two rounds of cell division
⇒ 4 daughter cells
one round of cell division
⇒ 2 daughter cells
Daughter cells with half the
amount of chromosomes as
parent cell
Daughter cells with same
amount of chromosomes
as parent cell
Crossing over results in genetic
variation
No crossing over
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Bio 115 Cells & Evolution of Life
Stages of Meiosis
Meiosis I
Meiosis II
prophase I
metaphase I
anaphase I
telophase I
cytokinesis
prophase II
metaphase II
anaphase II
telophase II
cytokinesis
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Bio 115 Cells & Evolution of Life
Prophase I: Crossing Over
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Bio 115 Cells & Evolution of Life
Homologous Chromosomes Separate During
Meiosis I
During anaphase I, homologous chromosomes
separate and move to opposite ends of the cell.
Sister chromatids remain attached to each other.
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Bio 115 Cells & Evolution of Life
Interkinesis: Preparations for Meiosis II
Telophase and
cytokinesis
of meiosis I
Interkinesis (some species)
⇒ Synthesize more cell
membrane, enzymes, etc.
No DNA replication!
Meiosis II
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Bio 115 Cells & Evolution of Life
Meiosis II: A Mitotic Division
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Bio 115 Cells & Evolution of Life
Meiosis Review
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Bio 115 Cells & Evolution of Life
Meiosis and Sexual Reproduction
Meiosis in parent 1
Meiosis in parent 2
genetically distinct egg cells (gametes)
genetically distinct sperm cells (gametes)
zygote
Each fertilization event results
in the combination of two unique gametes,
hence a genetically unique individual.
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Bio 115 Cells & Evolution of Life
Maintaining Ploidy Level
Meiosis in parent 1
Meiosis in parent 2
Gamete: ½ chromosomes
of parent
Gamete: ½ chromosomes
of parent
Zygote: same number of
chromosomes as parent
Reduction of chromosome number during meiosis I
assures species maintain same ploidy level (number of
sets of chromosomes)
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