Question

Which of the following events occurs only during meiosis and not in mitosis?

• A. Chromosome condensation
• B. Spindle formation
• C. Separation of sister chromatids
• D. Synapsis and crossing over of homologous chromosomes

Hint:

Crossing over during meiosis ensures genetic variation, which does not occur in mitosis.

Answer 1

The Correct Option is D

The event that occurs only during meiosis and not in mitosis is crossing-over between homologous chromosomes during prophase I.

Crossing-over is a process that occurs exclusively during meiosis, specifically in prophase I. During this phase, homologous chromosomes (chromosomes that have the same genes but possibly different alleles) pair up and exchange segments of their chromatids in a process known as genetic recombination.

This event leads to genetic diversity among the offspring, as it produces new combinations of alleles on each chromosome. The homologous chromosomes are then separated during meiosis I, and this unique event does not occur in mitosis, where the chromosomes do not undergo pairing or crossing-over.

Key difference between meiosis and mitosis:

• Meiosis: Includes two rounds of cell division (meiosis I and meiosis II), and crossing-over occurs in prophase I, leading to genetic variation.
• Mitosis: A single round of cell division that results in two genetically identical daughter cells, with no crossing-over occurring.

This difference is crucial for the generation of genetic diversity in sexually reproducing organisms.