Cell%20Division

1
Cell Division

• Meiosis

2
Definition

• Cell division by which eggs and sperm are
  produced.
• The production of sex cells, which are not
  genetically identical, through a series of cell
  divisions.

3

• Ensures that humans have the same number of
  chromosomes in each generation.

4

• It is a two-step process that reduces the
  chromosome number by halffrom 46 to 23to form
  sperm and egg cells.
• This is a reduction in genetic material.

5

• When the sperm and egg cells join at
  fertilization, each contributes 23 chromosomes so
  the resulting embryo will have the usual 46.

6

• Meiosis also allows genetic variation through a
  process of DNA shuffling while the cells are
  dividing.

7
Meiosis

• TWO divisions
• ONE DNA replication

8
Meiosis

• Interphase Before meiosis begins, genetic
  material is duplicated.
• First division of meiosis
• Prophase 1 Duplicated chromatin condenses. Each
  chromosome consists of two, closely associated
  sister chromatids. Crossing over can occur during
  the latter part of this stage.
• Metaphase 1 Homologous chromosomes align at the
  equatorial plate.
• Anaphase 1 Homologous pairs separate with sister
  chromatids remaining together.
• Telophase 1 Two daughter cells are formed with
  each daughter containing only one chromosome of
  the homologous pair.

9
Meiosis

• Second division of meiosis Gamete formation
• Prophase 2 DNA does not replicate.
• Metaphase 2 Chromosomes align at the equatorial
  plate.
• Anaphase 2 Centromeres divide and sister
  chromatids migrate separately to each pole.
• Telophase 2 Cell division is complete. Four
  haploid daughter cells are obtained.
• One parent cell produces four daughter cells.
  Daughter cells have half the number of
  chromosomes found in the original parent cell and
  with crossing over, are genetically different.

10
http//www.palaeos.com/
11
Crossing Over

• Where a section of one chromosome switches places
  with the same section from the other chromosome
  of the pair.
• Recombination

12
http//www.accessexcellence.org
13
http//post.queensu.ca/
14
Animation

• http//www.johnkyrk.com/meiosis.html

15
Animation

• http//www.csuchico.edu/jbell/Biol207/animations/
  meiosis.html

16
(No Transcript)