The testes of the grasshopper are removed and fixed in Carnoy’s fluid. After
2–14 hours, the testes are transferred to 10% alcohol and stored.
- 1 or 2 lobes of the testes are removed.
- The testes are placed on a glass slide.
- Apply 1 to 2 drops of acetocarmine stain.
- With a sharp blade, the teste lobes are cut into minute pieces and kept for
- The slide is then gently covered with a coverslip, taking care so that air
bubbles are not formed.
- Warm the slide gently and place it between 2 folds of filter paper.
- Press the material with the tip of the finger and remove the excess stain,
which comes out on the sides of the coverslip.
- The slide is observed under the microscope.
This phase is usually present in animal cells. The cells in this stage are
physiologically active. No DNA replication takes place.
- Leptotene. The chromosomes are long, standard, and uncoiled. They are densely
formed on 1 side of the cell. Only 1 sex chromosome occurs in the males,
which normally replicates later and hence appears as a dark skin body.
- Zygotene. Homologous chromosomes pair by a process called synapsis.
Pairing starts from many points on the chromosome. The chromosomes are
called bivalents. Bivalents become shortened and thickened by coiling and
condensation. Synapsis of a chromosome is cemented by a complex called
synaptonemal complex, which facilitates crossing over.
- Pachytene. Crossing over takes place between nonsister chromatids. Crossing
over is accompanied by the chiasmata formation.
- Diplotene. Condensation of chromatid material is greater. Each chromosome
can be distinguished separately.
- Diakinesis. Homologous chromosomes begin to coil and become shorter and
thicker. Chromosomes are fully contracted and deeply stained. The ‘X’
chromosome is rod-shaped, univalent, and easily distinguishable from the
rest of the chromosomes.
The chromosomes get oriented in the equatorial region of the spindle and their
centromeres are attached to the chromosomal fibers. Each chromosome is easily
seen. Maximum concentration occurs at this stage.
The spindle fibers contract and the homologous chromosomes separate and
move toward the opposite poles. Each chromosome consists of 2 chromatids
attached to 1 centromere.
The separation of homologous chromosomes is completed. They reach the
opposite poles. Two distinct daughter nuclei are formed. The daughter nuclei
formed contain only half the number of chromosomes present in the parent cell.
Cytokinesis may occur after the completion of telophase.
The chromosomes with 2 chromatids become short and thick.
This is the stage of the second meiotic division. The nuclear membrane and the
nucleolus are absent. The spindle is formed and the chromosomes are arranged
on the equator.
The spindle is formed. The centromeres of the daughter chromosomes are attached
to the spindle fibers. The 2 groups of the daughter chromosomes in each cell
have started moving apart toward the opposite poles of the spindle.
The 2 groups of daughter chromosomes in each haploid cell have reached the
2 poles of the spindle. The 2 haploid daughter cells formed as a result of first
meiotic division divide again by the second meiotic division. Four haploid cells
are formed from a single diploid cell.