1.Describe the phases of Prophase 1.Enumerate the chromosomal events during each stage.
2.What is tetrad?
3.Give significance of mitosis n meiosis
1. Prophase I − longest phase and is further sub-divided into 5 phases
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Leptotene − Condensation makes chromosomes become distinct and compact.
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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.
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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 terminalizes and chromosomes condense. Meiotic spindle assembles and nucleolus and nuclear envelope disappear.
2. During the Zygotene stage of prophase I of meiosis, the homologous chromosomes start pairing together by a process called synapsis to form a complex structure called synaptonemal complex. Two synaptonemal complexes further form a complex called bivalent or tetrad.
3. Significance of mitosis:
- It helps in maintaining the same number of chromosomes in daughter cells after division.
- It is responsible for growth and development of multicellular organisms.
- It helps in repairing of damaged tissues.
- It helps the cell to maintain proper size.
Significance of meiosis:
- From diploid cells haploid gametes are produced by this process
- It restricts the multiplication of chromosome numbers in every generation.
- It results in variation among the offspring due to crossing over.