Independent assortment refers to:

• A. Homologous chromosomes lining up during meiosis I
• B. Sister chromatids separating during meiosis II
• C. Random joining of two gametes
• D. Crossing over between homologous chromosomes

Answer: (A)

Independent assortment is about how homologous chromosomes are distributed into gametes during meiosis I. When these homologous pairs line up at the center of the cell, which member (maternal or paternal) goes into a given gamete is random, and each pair sorts independently of the others. This orientation creates many possible combinations of chromosomes in the gametes, quantified conceptually as 2^n if there are n chromosome pairs. This distinct process happens during meiosis I as the homologs separate. The separation of sister chromatids during meiosis II is a different step, not the basis of independent assortment. Crossing over in prophase I changes the alleles that may be carried on a chromosome but is separate from the random segregation of whole chromosomes. Random joining of gametes is fertilization, not how chromosomes are distributed during meiosis.