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Question
In which phase of meiosis are the following formed? Choose the answers from hint points given below.
a. Synaptonemal complex __________
b. Recombination nodules __________
c. Appearance/ activation of __________ enzyme recombinase
d. Termination of chiasmata __________
e. Interkinesis __________
f. Formation of dyad of cells __________
Hints :
1) Zygotene, 2) Pachytene, 3) Pachytene, 4) Diakinesis, 5) After Telophase-I/ before Meiosis-II, 6) Telophase-I/ After Meiosis-I.
a. Synaptonemal complex __________
b. Recombination nodules __________
c. Appearance/ activation of __________ enzyme recombinase
d. Termination of chiasmata __________
e. Interkinesis __________
f. Formation of dyad of cells __________
Hints :
1) Zygotene, 2) Pachytene, 3) Pachytene, 4) Diakinesis, 5) After Telophase-I/ before Meiosis-II, 6) Telophase-I/ After Meiosis-I.
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Solution
a. Synaptonemal complex
Zygotene, the second stage of meiosis I, is characterised by the pairing up of homologous chromosomes forming a complex structure called synaptonemal complex. These paired up homologous chromosomes are referred to as bivalents.
Final answer: Zygotene.
b. Recombination nodules
The exchange of segments between non-sister chromatids of homologous chromosomes, also known as crossing over, takes place in the third stage of meiosis I called pachytene stage. This is mediated due to the formation of recombination nodules between the non-sister chromatids of homologous chromosomes. These nodules contain certain enzymes like recombinase, which help in the process of recombination.
Final answer: Pachytene.
c. Appearance/ activation of enzyme recombinase
Crossing over is the process of exchange of DNA segments between the non-sister chromatids of homologous chromosomes. This process requires an enzyme called recombinase which helps in the exchange of DNA segments. This exchange of DNA segments is called recombination.
Final answer: Pachytene.
d. Termination of chiasmata
Diakinesis is the last and final phase of prophase-I of meiosis. In this phase, the terminalisation of the X- shaped structure called chiasmata occurs.
Final answer: Diakinesis.
e. Interkinesis
Interkinesis is a short-lived phase that occurs after the completion of meiosis-I but before prophase-II of meiosis-II.
Final answer: After Telophase-I/ before Meiosis-II.
f. Formation of dyad of cells
Telophase-I is characterised by the reappearance of the nucleolus and the nuclear membrane surrounding the chromatin at the opposite poles. Cytokinesis occurs after telophase-I resulting in the distribution of chromosomes into two cells. These two cells are referred to as the dyad of cells.
Final answer: Telophase-I/ After Meiosis-I.
Zygotene, the second stage of meiosis I, is characterised by the pairing up of homologous chromosomes forming a complex structure called synaptonemal complex. These paired up homologous chromosomes are referred to as bivalents.
Final answer: Zygotene.
b. Recombination nodules
The exchange of segments between non-sister chromatids of homologous chromosomes, also known as crossing over, takes place in the third stage of meiosis I called pachytene stage. This is mediated due to the formation of recombination nodules between the non-sister chromatids of homologous chromosomes. These nodules contain certain enzymes like recombinase, which help in the process of recombination.
Final answer: Pachytene.
c. Appearance/ activation of enzyme recombinase
Crossing over is the process of exchange of DNA segments between the non-sister chromatids of homologous chromosomes. This process requires an enzyme called recombinase which helps in the exchange of DNA segments. This exchange of DNA segments is called recombination.
Final answer: Pachytene.
d. Termination of chiasmata
Diakinesis is the last and final phase of prophase-I of meiosis. In this phase, the terminalisation of the X- shaped structure called chiasmata occurs.
Final answer: Diakinesis.
e. Interkinesis
Interkinesis is a short-lived phase that occurs after the completion of meiosis-I but before prophase-II of meiosis-II.
Final answer: After Telophase-I/ before Meiosis-II.
f. Formation of dyad of cells
Telophase-I is characterised by the reappearance of the nucleolus and the nuclear membrane surrounding the chromatin at the opposite poles. Cytokinesis occurs after telophase-I resulting in the distribution of chromosomes into two cells. These two cells are referred to as the dyad of cells.
Final answer: Telophase-I/ After Meiosis-I.
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