Page 43 - Biology - XII

4. Types of meiosis are:
(a) Zygotic or Initial meiosis (Haplotonic pattern), e.g. thallophyta.
(b) Gametic or Terminal meiosis (Diplotonic pattern), e.g. animals and higher plants.

(c) Sporic or Intermediate meiosis (Diplohaplotonic pattern), e.g. some thallophytes, but not in
animals.

n
Meiosis II
n
n
Meiosis I Equational 4 Daughter Gametes
2 Daughter cells (sex cells)
Reductional division cells Haploid cells
Parent Division n
cell (2n) n Meiosis II
n

Fig. 8.2: Scheme of meiosis cell division

Materials Required
Permanent slides and compound microscope

Procedure
1. Clean the slide and keep it on the stage of compound microscope.
2. Focus the slide under 10X (low power of microscope) and observe it.
3. Then, shift the objective lens and observe under 45X (high power) for magnifi ed structure.
4. Study the slide and draw the fi gure of various stages observed.

SPOT - 1

Meiosis in Onion Bud

Observations
1. Spores/pollens at their diff erent stages of development.
2. Cells are single, double, or at tetrad stages.

If cluster of cells are seen, tap the coverslip again to scatter them. Identify any one stage and observe it.

Comments
Prophase I
The prophase of 1st division of meiosis has fi ve subdivisions.
1. Leptotene (Leptos—thin). This stage is identifi ed by—
(a) The nucleus enlarges in size and occupies most of the cell volume.
(b) The chromatin material forms long slender thread-like structures called chromosomes.

(c) Nuclear membrane is clear.
(d) Nucleolus is also seen.

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