Meiosis in onion bud cell or grasshopper testis through permanent slides

Aim: Meiosis in onion bud cell or grasshopper testis through permanent slides

Theory:

1. Meiosis is a double division which occurs in diploid cells and give rise to four haploid cells each having half the number of chromosomes as compared to the parent cells.

2. It occurs in cells that produce gametes in sexually reproducing organisms.

3. The male gametes (sperms) are produced in testes and the female gametes (egg's) are produced in the ovaries through meiosis.

4. Meiosis comprises of two division- meiosis I and meiosis II. Meiosis I result in reduction of chromosomes number into half. i.e from 2n to n. hence is called reductional division. Meiosis II maintains same number of chromosomes, hence is called equational division.

Material / Apparatus Required:

• Permanents slides of different stages of meiosis
• Microscope

Procedure:

1. Fix the permanent slide under the microscope.
2. First observe it under the low power and then under high power of the microscope.

Observation:

A. Meiosis I (reductional division or heterotypic)

i. Prophase I

• Leptotene: appearance of beaded chromosomes.
• Zygotene: pairing of homologous chromosomes.
• Pachytene: formation of tetrad, crossing over and chaismata formation.
• Diplotene: Two chromosomes of each bivalent move away and chaismata disappears.
• Diakinesis: nucleolus and nuclear envelope disappear and spindle begin to formed.

ii. Metaphase I: Formation of spindle and arrangement of chromosome at equator.

iii. Anaphase I: Separation of homologous chromosome and their movement towards2 opposite2222 poles of the spindle.

iv. Telophase I: Formation of two haploid nuclei.

B. Meiosis II (homotypic or equational division)

i. Prophase I: Sister chromosome of each chromosome begins to condense.

ii. Metaphase II: Formation of spindle, arrangement of chromosome at equator.

iii. Anaphase II: Movement of daughter chromosomes towards pole of spindle.

iv. Telophase II: Formation of two daughter nuclei from each daughter cell formed by meiosis I.

C. Cytokinesis: division of cytoplasm resulting into four haploid daughter cells form a diploid cell.

Precautions:

1. First observe the slide under low power and then under high power of the microscope.
2. Use fine adjustment of the microscope for focusing the slide under high power.