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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
The diagram given below represents a certain stage of mitosis:
- Identify the stage of cell division.
- Name the parts labelled A and B.
- What is the unique feature observed in this stage?
- How many daughter cells are formed from this type of cell division?
The diagram given below represents a stage during cell division.
Study the same and answer the questions that follow:
- Identify whether it is a plant cell or an animal cell. Give a reason in support of your answer.
- Name the stage depicted in the diagram. What is the unique feature observed in this stage?
- Name the type of cell division that occurs during:
- Replacement of old leaves by new ones
- Formation of gametes
- What is the stage that comes before the stage shown in the diagram?
- Draw a neat, labelled diagram of the stage mentioned in (iv) above keeping the chromosome number constant.
For formation of plasma membrane, ______ molecules are necessary.
Describe anaphase in mitosis.
Define the following:
Karyokinesis
Fill in the blank:
______ takes place in body cells resulting in growth and development.
Choose the correct answer:
Which division takes most time?
Identify the stages of mitosis given below and label the figures.
Explain the Term Pachytene
Explain the Term Cell Diakinesis
Name the Following
The stage when chromosomes arrange at the equator.
Name the Following
Name the stage during which nuclear membrane and nucleoli reappear.
Write the functional activity of the following structure:
Colchicine
The karyotype (set of chromosomes) shown below is taken from a dividing cell in a certain individual.
(i) Is the individual male or female? Explain your answer.
(ii) How would you expect
(a) a female cell and
(b) sperm cell to differ in chromosome composition?
Identify the stage of mitosis from the below picture. List the chromosomal events in this stage.
The diagram given below represents a stage in mitosis.
- Identify the stage given above.
- Give one reason to support your answer in (a).
- Mention the number of chromosomes given in the diagram.
