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प्रश्न
With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.
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उत्तर
Prophase-I is the first stage of meiosis-I and is the longest and most important stage. It is divided into five sub-stages:
1. Leptotene
- Chromosomes begin to condense.
- They become long, thin, and distinct.
2. Zygotene
- Homologous chromosomes pair together by a process called synapsis.
- A synaptonemal complex is formed.
- Paired chromosomes form bivalents or tetrads.
3. Pachytene
- It is the longest stage of Prophase-I.
- Chromosomes become shorter and thicker.
- Crossing over occurs between non-sister chromatids of homologous chromosomes.
- Recombination nodules appear at crossing-over sites
4. Diplotene
- Synaptonemal complex dissolves.
- Homologous chromosomes begin to separate.
- Chiasmata appear at crossover points.
5. Diakinesis
- Chiasmata terminalise.
- Chromosomes condense further.
- The nuclear membrane and nucleolus disappear.
- Meiotic spindle fibres begin to form.
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संबंधित प्रश्न
Given below is a diagram representing a stage during mitotic cell division in an animal cell Examine it carefully and answer the questions which follow.
- Identify the stage. Give one reason in support of your answer.
- Name the cell organelle that forms the ‘aster’.
- Name the parts labelled 1, 2 and 3.
- Name the stage that follows the one shown above; how is that stage identified?
- Mention two differences between mitosis and meiosis with regards to:
- The number of daughter cells produced.
- The chromosome number in the daughter cells.
For formation of plasma membrane, ______ molecules are necessary.
The diagram given alongside represents a stage in cell division.
Study the same and answer the questions that follow:
(i) Identify the stage of cell division.
(ii) Name the parts labeled A,B,C and D.
(iii) What is the unique feature observed in this stage?
(iv) Where does this type of cell division usually occur?
(v) How many daughter cells are formed from this type of cell division?
(vi) Is the dividing cell shown a plant or an animal cell?
Give a reason to support your answer.
Choose the correct answer:
Which division takes most time?
Explain the Term Pachytene
Name the following:
The kind of division normally seen at the tip of the root and shoot system.
Name the Following
The stage when chromosomes arrange at the equator.
Name the Following
Nuclear envelope and nucleoli reappear in which stage.
Mention, if the following statement is True or False. If false rewrite the wrong statement in its correct form:
The alkaloid colchicine inhibits the formation of the mitotic spindle.
Multiple Choice Question:
The nuclear membrane and nucleolus become indistinguishable during
Column ‘II’ is a list of items related to ideas in Column ‘I’. Match the terms in Column ‘II’ with a suitable idea given in Column ‘I’.
| Column I | Column II |
| (i) Anaphase | (a) Chromosomes become arranged in a horizontal plane at the equator. |
| (ii) Prophase | (b) Daughter chromosomes move to opposite poles of the spindle. |
| (iii) Telophase | (c) Chromosomes become visible as fine, long threads. |
| (iv) Metaphase | (d) Chromosomes lose their distinctiveness and gradually become transformed into chromatin network. |
Give the sequence of the events occurring during the prophase of mitosis.
Identify the stage of mitosis from the below picture. List the chromosomal events in this stage.
During Mitosis what is the position of chromatids in metaphase?
The phase of karyokinesis which is almost the reverse of prophase is ______.
