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Question
With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.
Solution
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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