Which process is crucial for genetic variation during reproduction?

Meiosis is the process crucial for genetic variation during reproduction because it involves two rounds of cell division that produce gametes (sperm and egg cells) with half the original number of chromosomes. During meiosis, genetic recombination occurs through crossing over, where homologous chromosomes exchange segments of genetic material. This not only shuffles alleles but also creates new combinations of genes, leading to increased genetic diversity in the offspring.

Additionally, meiosis ensures that gametes are haploid, which means they contain only one set of chromosomes. When fertilization occurs, the fusion of two haploid gametes restores the diploid state in the zygote, introducing a mixture of genetic material from both parents. This variation is fundamental in evolution and adaptation, as it provides a basis for natural selection to act upon.

In contrast, mitosis, replication, and transcription serve different roles in cell division, DNA duplication, and gene expression respectively. Mitosis results in two identical daughter cells, making it key for growth and repair rather than variation. Replication involves copying DNA, ensuring fidelity rather than diversity. Transcription is about producing RNA from DNA, which is essential for expressing genes but does not directly contribute to genetic variation.