Cell Division

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Cell Division

• Meiosis

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Relationship Between Meiosis and Genetics

• Meiosis results in egg (females) and sperm
  (males) cells.
• When egg and sperm combine a new human is formed.
• The egg carries the genes from mom and the sperm
  carries the genes from dad
• You are a combination of genes from your mom and
  your dad!
• Your eye color, hair color etc. all depends on
  which egg cell and sperm cells combine!

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Let Us Review Mitosis

• Cellular division involving replication and
  division of chromosomes (DNA).
• New cell contains complete set of chromosomes.
  (Two copies of genetic info.)
• Results in DIPLOID cells (chromosomes occur in
  pairs)

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Diploid Cells

• Chromosomes after replication (ready for mitosis)

• Chromosomes in early interphase (actually
  chromatin)

Both are Diploid
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Diploid Cells cont.

• All body cells are diploid.
• Sex cells egg and sperm are the only monoploid
  cells

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Sex Cells

• Germ Cells
• Also know as Sex Cells
• Only contain one copy of genetic information
• Have one chromosome of each pair or half that of
  diploid cells.
• Haploid (N) state.

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of Chromosomes
Total Chromosomes in a diploid cell of homologous pairs in a diploid cell Total chromosomes in haploid cell
HUMAN 46
CAT 36
23
23
18
18
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Why is Haploid Important?

• If diploid cells are fertilized

2N 2N ? 4N
Chromosome will keep doubling!!
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Why is Haploid Important?

• If haploid cells are fertilized

N N ? 2N
Like all cells of the body!!
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Sexual Reproduction

• Reproductive process in which haploid sex cells
  (gametes) fuse to produce a diploid fertilized
  egg (zygote)

EGG SPERM Fertilized Egg
(ZYGOTE)
GAMETES
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MEIOSIS

• Cell division that reduces the number of
  chromosomes in half
• Occurs in sex cells (germ cells Egg and Sperm)
• Two Divisions
• MEIOSIS I
• MEIOSIS II

Meiosis I
Meiosis II
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Prophase I

• Chromosomes form
• Nuclear membrane and nucleolus disappear
• Synapsis homologous chromosomes pair up
• Crossing Over exchange of DNA creating genetic
  variability

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Metaphase I

• Homologous chromosomes line up at the equator

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Anaphase I / Telophase I

• ANAPHASE I
• Homologous chromosomes separate and move to
  opposite poles
• Cells are still diploid
• TELOPHASE I
• Cell membrane pinches in

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Interphase????
There is NO interphase between Meiosis I and
Meiosis II
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Prophase II

• Cells are diploid.
• Cells get ready to divide again.

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Metaphase II

• Chromosomes align at the equator
• Looks like mitosis

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Anaphase II / Telophase II

• ANAPHASE II
• Sister chromatids move to opposite poles
• TELOPHASE II
• Cell membrane
• pinches in
• Nuclear membrane
• reappears.

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Resulting Sex Cells

• Four HAPLOID sex cells are produced.

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MEIOSIS