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The critical event of meiosis is the crossing over. It occurs during:
a. Leptotene
b. Pachytene
c. Diplotene
d. Zygotene

Answer Verified Verified
Hint: A distinct type of cell detachment in sexually replicating creatures made use to produce the gametes, such as sperm or egg cells is called Meiosis.

Complete answer:
Meiosis is a process wherein a single cell divides twice to generate four cells comprising half the innovative amount of genetic info is the process of Meiosis. We are now aware that the process that takes place between homologous chromosomes in demand to upsurge hereditary assortment is called crossing over.

The Leptotene is the stage where we observe that the chromosomes begin to repel each other and separate themselves from each other longitudinally.

This permits for genomic assortment, which will benefit cells to take part in the existence of the rightest and progression. A defining characteristic of meiosis is the combination of homologous chromosomes.

The second stage of the prophase of the process of meiosis, which follows leptotene, during which homologous chromosomes begin to pair is Zygotene. It is not a critical period in which crossing over occurs.

During the period in which the corresponding chromosomes shorten and thicken, the two chromatids of each distinct, and change in segments amid chromatids may arise is Pachytene. Crossing over is known to be one of the most imperative characteristics of the process of meiosis. You can see that this process takes place during the fourth stage of the first prophase of meiosis in the procedure of gametogenesis. This stage is called Diplotene.

You can observe that the pairing of Homologous chromosomes takes place during the prophase stage of meiosis I. The prophase stage of meiosis I comprises zygotene, diakinesis, leptotene, pachytene, substages, and diplotene stages. A physical replacement of equal parts of adjacent non-sister chromatids is the process of Crossing over.

In the next step, on careful observation, we can see the chromatids breakdown and maybe recommitted to a different homologous chromosome when crossing over takes place during the stage of pachytene between non-sister chromatids of a twosome of homologous chromosomes.

Hence, The correct answer is option (B).

Note: We should note that during the process of crossing over, a part of one chromosome is swapped or switched with another. Normally, a hybrid chromosome with an exclusive shape of genetic material is the outcome. Moreover, we can also perceive that the gametes gain the capability to be hereditarily dissimilar from their neighboring gametes after passing over befalls.