Question

Crossing over occurs during
A. Leptotene
B. Pachytene
C. Diplotene
D. Diakinesis

Answer 1

Meiosis is a type of cell division that occurs in sexually reproducing organisms' germ cells and is used to produce gametes such as sperm and egg cells. It takes two rounds of division to produce four cells, each with only one copy of each chromosome.

Complete answer:
Chromosomal crossover, also known as crossing over, is the exchange of genetic material between two homologous chromosomes' non-sister chromatids during sexual reproduction, resulting in recombinant chromosomes. It is one of the final stages of genetic recombination, which occurs during synapsis in the pachytene stage of prophase I of meiosis. Synapsis begins before the formation of the synaptonemal complex and is not completed until late in prophase I. When matching regions on matching chromosomes break and reconnect to the other chromosome, this is known as crossover.
A distinguishing feature of meiosis is the pairing of homologous chromosomes. During the prophase stage of meiosis I, homologous chromosomes pair. Leptotene, zygotene, pachytene, diplotene, and diakinesis are substages of the prophase stage of meiosis I. The physical exchange of equal pieces of adjacent non-sister chromatids is known as crossing over.
When chromatids cross over, they break and may be reattached to another homologous chromosome. During the pachytene stage, non-sister chromatids of a pair of homologous chromosomes cross over.

As a result, option B: Pachytene is the correct answer.

Note:
The crossing-over value is the frequency with which two gene loci (markers) cross over. Recombination in a specific region of a linkage structure (chromosome) tends to be constant under a fixed set of genetic and environmental conditions, and the same is true for the crossing-over value used in the production of genetic maps.