Which statement best describes independent assortment?

• A. It is the random alignment of chromosomes on the spindle during metaphase II.
• B. It occurs during prophase I.
• C. It is identical to crossing over.
• D. It describes the random distribution of maternal and paternal chromosomes into gametes, contributing to genetic variation.

Answer: (D)

Independent assortment describes how chromosomes from each pair are distributed into gametes in a random way, so the maternal and paternal chromosomes are sorted independently. This occurs as homologous chromosome pairs align and separate during meiosis I, and the orientation of each pair is random, producing many possible combinations of chromosomes in gametes. This randomness creates genetic variation in offspring because each gamete can carry different mixes of maternal and paternal chromosomes. The other statements mix up the stage or process: random alignment during metaphase II involves sister chromatids, not homologous pairs; prophase I is when crossing over happens, which reshuffles alleles within chromosomes, not the distribution of whole chromosomes. Crossing over is a separate mechanism from independent assortment.