The process of appearance of recombination nodules occurs at which sub stage of prophase I in meiosis?
The process of appearance of recombination nodules occurs at which sub stage of prophase I in meiosis?
Pachytene
Diplotene
Diakinesis
Zygoten
The Correct Option is A
Solution and Explanation
Correct Answer: Option 1 – Pachytene
The process of appearance of recombination nodules occurs during the pachytene stage of prophase I in meiosis. This is one of the most critical and dynamic sub-stages of meiosis, where genetic variation is introduced through the process of crossing over.
Meiosis I is divided into several sub-stages: leptotene, zygotene, pachytene, diplotene, and diakinesis. Each stage plays a unique role in the preparation and recombination of homologous chromosomes.
During pachytene, the following key events occur:
- Homologous chromosomes are fully paired and tightly synapsed via the synaptonemal complex.
- Recombination nodules appear along the synaptonemal complex. These nodules are protein structures that mediate the exchange of genetic material between non-sister chromatids.
- Crossing over (genetic recombination) occurs at the sites of these nodules, leading to new combinations of genes — a fundamental mechanism for increasing genetic diversity in sexually reproducing organisms.
Explanation of Other Options:
Option 2 – Diplotene: In this stage, the synaptonemal complex dissolves and homologous chromosomes begin to separate, but are held together at chiasmata (sites where crossing over has already occurred). No new recombination nodules appear at this stage.
Option 3 – Diakinesis: This is the final stage of prophase I where chromosomes condense further and prepare for metaphase. The chiasmata are still visible, but the recombination process is already complete.
Option 4 – Zygotene: This stage is characterized by the beginning of synapsis between homologous chromosomes, but recombination nodules have not yet appeared. Their formation begins in the next stage — pachytene.
Conclusion: Recombination nodules, essential for genetic exchange during meiosis, appear in the pachytene stage of prophase I. This stage is vital for ensuring genetic variation through the formation of chiasmata and crossing over, a key topic in cell biology and frequently asked in NEET and other competitive exams.
Top Questions on Meiosis
Match the stages of prophase I given in Column-I with their features in Column-II and choose the correct options from the choices given below:
- In karyokinesis of meiosis - I, which of the following separates?
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- The correct sequence of events in prophase I is
- Which of the following stages of meiosis involves division of centromere?
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Concepts Used:
Meiosis
Meiosis is a process in which a single cell, a diploid cell, undergoes division twice to produce four haploid daughter cells, and the cells produced are known as the sex cells or gametes (sperms in males and egg in females). It contains half of the original amount of genetic information. The haploids only have half the number of chromosomes of the parent cell.
Features of Meiosis:
- It results in the formation of four daughter cells in each cycle of cell division.
- The daughter cells are identical to the mother cell in shape and size but different in chromosome number.
- The daughter cells are haploid.
- Recombination and segregation take place in meiosis.
- The process occurs in the reproductive organs and results in the formation of gametes.
- The process is divided into two types-Meiosis-I reduces the chromosome number to half and is known as reductional division. Meiosis-II is just like the mitotic division.
Phases of Meiosis
Meiosis can be divided into nine stages. The process is usually divided into two parts. The first time a cell divides (meiosis I) and the second time it divides (meiosis II). The phases are as follows –
Meiosis 1 Stages
The different stages of meiosis 1 can be explained by the following phases :
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1
Meiosis 2 Stages
The different stages of meiosis 1 can be explained by the following phases :
- Prophase 2
- Metaphase 2
- Anaphase 2
- Telophase 2