Meiosis

1
Meiosis Grasshopper predivision nuclei

• These two nuclei were stained with Feulgen.
  Heterochromatin is visible, but chromosomes are
  not. DNA replication and chromosome duplication
  have occurred, but the latter will not be seen
  until later.

2
Meiosis Very early Prophase 1

• Chromosomes are condensing and so are beginning
  to become visible as threads.

3
Meiosis Early Prophase 1

• Homologous chromosomes have paired. The dark
  blob at the left is heterochromatin.

4
Meiosis Mid Prophase 1

• Pairing is complete. This is the time that
  chiasma form, but we cannot see this through the
  optical microscope.

5
Meiosis Late Prophase 1

• The attraction between the homologous chromosomes
  has given way to repulsion. Chiasmata and the
  result of chromosome duplication are clear.

6
Meiosis Late Prophase 1 Another picture

• The attraction between the homologous chromosomes
  has given way to repulsion. Chiasmata and the
  result of chromosome duplication are clear.

7
Meiosis Metaphase 1

• The spindle has formed (it has not been stained),
  the chromosomes have attached to spindle fibers
  and are now aligned with the centromeres of the
  paired homologues on opposite side of the
  metaphase plate.

8
Meiosis Anaphase 1

• The homologous pairs of chromosomes are now
  separating from each other, moving to opposite
  poles of the spindle.

9
Meiosis Late Anaphase 1

• Homologous chromosomes are fully separated.
  Products of chromosome duplication and crossing
  over have stayed together. There are 9 duplicated
  chromosomes at left, 8 at the right.

10
Meiosis Very Late Anaphase 1

• The heterochromatic X-chromosome appears fainter
  at the top of the right group.

11
Meiosis Metaphase 2

• Polar view of chromo-somes arranged approximately
  in a circle. Chomosomes with a centromere near
  the middle appear to have 4 arms, while those
  with terminal centromeres have only 2 arms.

12
Meiosis- Metaphase 2

• Equatorial view, including the X-chromosome

13
Meiosis Anaphase 2

• Eight separating from eight. Thus there is no
  X-chromosome here.