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Stages of Meiosis, Mitosis and Meiosis, Meiosis and Genetic Information
Essential Question:
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How has genetics played into allowing every organism to survive as long as they have?

Focus Question:
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What are the stages of meiosis?
How do mitosis and meiosis differ?
How does Meiosis make sure that the genetic information is varied?

Think
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What is the end result of meiosis?

Stages of Meiosis
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Meiosis is a form of cell division that produces daughter cells with half the number of chromosomes that
are in the parent cell
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In meiosis I, homologous chromosomes are separated
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Meiosis I
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Meiosis begins with a diploid cell that has copied its chromosomes
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Homologous
chromosomes pair
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In metaphase I, the spindle moves the pairs of homologous chromosomes to the equator of the cell
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Prophase I and Metaphase I

Meiosis I
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In anaphase I, the homologous chromosomes separate
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But the chromatids do not separate at their centromeres
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The genetic material, however, has recombined
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Both cells have
one chromosome from each pair of homologous chromosomes
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The chromosomes are not copied between meiosis I and meiosis II
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During metaphase II, the chromosomes line up along the equators and are attached at their centromeres
to spindle fibers
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The chromatids, which are now called chromosomes, move to
opposite poles of the cell
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The spindle breaks
down, and the cell goes through cytokinesis
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Anaphase II Telophase II and Cytokinesis

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Review:
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What are the stages of meiosis and a brief description of what happens in each?

Think:
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How is the end result of meiosis different from mitosis?
make a Venn Diagram to compare and contrast meiosis to mitosis
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Meiosis

Mitosis

Comparing Mitosis and Meiosis
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The processes of mitosis and meiosis are similar but meet different needs and have different results
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Meiosis makes cells that enable an organism to reproduce sexually and happens only in reproductive
structures
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Meiosis produces four genetically different haploid cells
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If you compare meiosis and mitosis, they may appear similar but they are very different
In prophase I of meiosis, every chromosome pairs with its homologue
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As the tetrads form, different homologues exchange parts of their chromatids in the process of crossingover
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Therefore, a main difference between meiosis and mitosis is that in meiosis, genetic information is
rearranged leading to genetic variation in offspring
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Genetic variation can help a population survive a major environmental change
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In sexual reproduction, existing genes are rearranged
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Fusion of haploid cells from two different individuals adds further variation
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Crossing-Over
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During prophase I, homologous chromosomes pair up
Crossing-over happens when one arm of a chromatid crosses over the arm of the other chromatid
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Thus, the sister chromatids of a homologous chromosome no longer have identical genetic information
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The two pairs of chromosomes can line up in either of two equally probable ways
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Random Fertilization
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Fertilization is a random process that adds genetic variation
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Because fertilization of an egg by a sperm is random, the number of possible outcomes is squared
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Mitosis produces cells that are used during growth, development, repair, and asexual reproduction
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Three key contributions to genetic variation are crossing-over, independent assortment, and random
fertilization

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