What occurs during prophase I that increases genetic variation?

• A. DNA replication
• B. Nuclear dissolution
• C. Cytokinesis
• D. Crossing over

Answer: (D)

During meiosis, genetic variation is heightened by crossing over in prophase I. Here, homologous chromosomes pair up in synapsis to form tetrads, and nonsister chromatids exchange DNA segments at crossover points. This recombination produces chromatids with new maternal and paternal allele combinations, so the gametes that result carry novel genetic mixes. This event is specific to prophase I and directly creates diversity among offspring.

DNA replication happens earlier in the cell cycle (before meiosis) and simply duplicates the genome, not generating new allele combinations. Nuclear envelope breakdown is a structural change that allows chromosome movement but doesn’t alter genetic content. Cytokinesis splits the cell after division and does not affect allele combinations.