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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 longest phase of meiosis and is further sub divided into 5 phases:
- Leptotene
Condensation makes chromosomes become distinct and compact. - Zygotene
Homologous chromosomes start pairing together by a process called synapsis to form a complex structure called synaptonemal complex. Two synapsed homologous chromosomes form a complex called bivalent or tetrad. - Pachytene
Longest phase of prophase I
Recombination nodules appear in this stage at the sites where crossing over has to take place between non-sister chromatids of homologous chromosomes. - Diplotene
Synaptonemal complex dissolves and recombinants separate from each other except at crossover sites to form X-shaped structure called chiasmata. - Diakinesis
Chiasmata terminalises and chromosomes condense. Meiotic spindle assembles and nucleolus and nuclear envelope disappear.
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संबंधित प्रश्न
Fill in the blank and explain the statement.
For formation of plasma membrane, ____________ molecules are necessary.
Describe anaphase in mitosis.
Define the following:
Karyokinesis
Fill in the blank:
______ is the indirect cell division.
Choose the correct answer:
Which division takes most time?
The figure below shows a certain stage of mitosis:
(i) Name the stage,
(ii) Label the parts 1 to 4
(iii) How many chromosomes are shown here?
Give Technical Terms
The stage in mitosis when the nucleolus starts disappearing.
Complete the following sentence with appropriate word :
______means the splitting of the nucleus.
Complete the following sentence with appropriate word :
Colchicine arrests cell division at __________.
Choose the Odd One Out
Multiple Choice Question:
The nuclear membrane disappears in
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. |
Explain the following figure.
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?
Name these:
Two steps of the process Mitosis
What is the main function of the spindle fibres during mitosis?
