To Study the Stages of Meiosis in Onion Bud Cells or Grasshopper Testis Through Permanent Slides

You must be knowing that all germ cells divide by meiosis. One cell after meiosis forms four cells. Meiosis occurs in two stages: meiosis I and meiosis II. Meiosis is known as reductional division because chromosome number is reduced to half in this division. Meiosis leads to variation. Continuous accumulated variation leads to evolution. All of you must have seen the grasshopper or grasshopper diagram. It is widely used for studying meiosis. To know more about this experiment and meiosis continue reading this article.

Table of Content

• Aim

• Articles Required

• Theory

• Procedure

• Observations

• Result

• Precautions

• Lab Manual Questions

• Viva Questions

• Practical Based Questions

• Summary

Aim

To study meiosis in onion bud cells or grasshopper testis through permanent slides

Articles Required

• Permanent slides

• Microscope

Theory

Meiosis is a double division that occurs in diploid reproductive cells. It leads to variation and evolution. It occurs in two steps, meiosis I and meiosis II. Meiosis II is the same as mitosis. Meiosis I occurs in two steps: karyokinesis and cytokinesis. Karyokinesis is divided into four stages: prophase, metaphase, anaphase, and telophase. Prophase is of five stages - leptotene, zygotene, pachytene, diplotene, and diakinesis.

Procedure

• Fix the permanent slides under the microscope

• First, observe slides under a low power microscope, and  then high power microscope

Observations

The different stages of meiosis are observed in high-power microscopes. The characteristics of different stages of meiosis are explained below:

Meiosis 1

There are four phases of nuclear division in meiosis 1.

Prophase 1 

In meiosis, there are five stages of prophase 1, and it is the longest phase of nuclear division. 

• Leptotene - in this stage, chromatin fibres become condensed and form a thick thread-like structure called chromosomes

• Zygotene - In this stage, homologous chromosomes paired together to form bivalent or tetrad

• Pachytene - In this stage, there is a crossing over between non-sister chromatids of homologous chromosomes. In this stage, tetrad appears more clearly.

• Diplotene - In this stage, there is the separation of non-sister chromatids except at some sites which are known as chiasmata. A chiasma is an x-shaped structure that represents the site of crossover. 

• Diakinesis - This is the last stage of meiosis 1. In this stage, homologous chromosomes appear thick and ring-shaped, and the nucleus membrane and nucleolus disappear, and spindle fibres also start to form.

Metaphase 1 

In this stage, all paired homologous chromosomes are arranged at the centre of the nucleus, which is known as the equatorial plane, and the equatorial plate can be seen in metaphase 1. Bivalent or tetrad are visible in this stage.

Anaphase 1 

In this phase, homologous chromosomes separate from each other and move toward opposite poles. Now each pole has half the number of chromosomes with two chromatids.

Telophase1

It is the last phase of karyokinesis, in this phase chromosomes condensed to form future daughter nuclei, and nucleolus and nuclear membrane reappear.

After karyokinesis, cytokinesis occurs and leads to the formation of two daughter nuclei.

Interkinesis

Interkinesis is defined as the period of rest between meiosis 1 and meiosis 2. Sometimes interkinesis is also known as interphase. But during this phase, there is no DNA replication.

Meiosis II

Two cells formed by meiosis 1 undergo further division to make four cells. There are two stages of meiosis 2, first karyokinesis and cytokinesis. Meiosis II is the same as mitosis.

Prophase II 

The chromosomes of daughter cells begin to condense and become thick, and at the last of this stage nucleolus and nuclear membrane begin to disappear.

Metaphase II 

The chromosomes are arranged at the equator. All chromosomes are arranged at the equatorial plate. In this stage, two spindle fibers are attached to each chromosome from opposite poles.

Anaphase II 

The sister chromatids of homologous chromosomes separate from each other and move toward opposite poles. And each pole receives the same number of chromosomes as that in parent nuclei.

Telophase II 

This is the last stage of meiosis. The nuclear membrane and nucleolus reappear and chromosomes condensed to form future daughter nuclei. 

Stages of meiosis

Result 

The various stages of meiosis are distinctly seen under the microscope. 

Precautions 

Following precautions must be taken while experimenting

• Slides must be cleaned before use

• Place slides under the microscope carefully. 

Lab Manual Questions 

Q1. What is the significance of Meiosis?

Ans: meiosis is necessary for evolution, and also it maintains chromosome numbers in sexually reproducing organisms.

Q2. What is crossing over?

Ans: Crossing over is the process of exchanging genetic material between non-sister chromatids of homologous chromosomes.

Q3. At what stages does crossing over take place? 

Ans: Crossing over takes place in the pachytene stage.

Viva Questions 

Q1. What is meiosis?

Ans: It is a type of reductional division in which chromosome numbers get halved. It occurs in sexually reproducing organisms. Gametes are formed by reductional division. 

Q2. What is the purpose of meiosis in plants?

Ans: Meiosis is a type of reductional division used to produce gametes or sex cells by meiosis. In this, four cells are produced from one cell.

Q3. What is spermatogenesis?

Ans: Spermatogenesis is defined as the process of formation of sperms from primordial germ cells. These cells are formed by meiosis division. 

Q4. Why is meiosis  II known as equational division?

Ans: Meiosis II is equational division because, in meiosis, chromosome number remains the same in divided cells. 

Q5. What are the different stages of meiosis?

Ans: There are many different stages of meiosis. These stages are given here- interphase, prophase1, metaphase 1, anaphase1, telophase1, cytokinesis, interphase II, prophase II, metaphase II, anaphase II, and telophase II. 

Q6. Does meiosis occur in an onion cell?

Ans: Onion root tip is only used for mitotic study, as they are meristematic cells and do not exhibit meiosis. 

Q7. In meiotic division, how many times DNA replication occurs?

Ans: In meiosis, replication occurs only one time, whereas division occurs twice. Meiosis I and Meiosis II are two divisions of meiosis.

Q8. What is the main function of meiosis?

Ans: Meiosis is used to produce gamete cells from germ cells. Here one germ cell divides to form four gametes. And in meiosis, the chromosome number is reduced to half. 

Practical Based Questions 

Q1. Why is a grasshopper used in the study of meiosis?

1. Due to smaller chromosome size 

2. Due to larger chromosome size 

3. Due to more chromosome 

4. None of the above

Ans: 2. Due to larger chromosome size 

Q2. In which cells of testis meiosis take place?

1. Spermatid 

2. Spermatogonia 

3. Spermatocytes 

4. Sperm 

Ans: 3. Spermatocytes

Q3. Who invented meiosis

1. Hertwig 

2. Robert brown 

3. Landsteiner 

4. None of the above 

Ans: 1. Hertwig

Q4. A bivalent consists of how many chromatids and chromosomes

1. 1 chromosome and 4 chromatids

2. 1 chromosome and 2 chromatids

3. 2 chromosomes and 4 chromatids 

4. None of the above 

Ans: 3. 2 chromosomes and 4 chromatids.

Q5. During cell division spindle fibers attached to which parts of chromosomes

1. Kinetochore 

2. Centromere 

3. Telomere 

4. None of the above 

Ans: 1. Kinetochore

Q6. Continuous variations are produced in which division

1. Mitosis 

2. Meiosis 

3. Both of the above

4. None of the above 

Ans: 2. Meiosis

Q7. How many cells are formed after one meiosis? 

1. 2 cells 

2. 6 cells 

3. 3 cells 

4. 4 cells 

Ans: 4. 4 cells

Q8. If there are four chromosomes in a cell, then after meiosis 1 how many chromosomes will be there?

1. 4 chromosomes 

2. 3 chromosomes 

3. 2 chromosomes 

4. None of the above 

Ans: 3. 2 chromosomes.

Conclusion 

• In this article, we have discussed meiosis in onion bud cells or Grasshopper cells

• We have seen various stages of meiosis under a microscope

• There are two phases of meiosis. Meiosis I and meiosis II. The Karyokinesis of meiosis takes place in four steps 

• Meiosis is necessary for variation and evolution

• Meiosis II is the same as mitosis.