Mendel's observation that most genes assort independently is explained by...

• A. Most genes are on different chromosomes
• B. All genes on the same chromosome assort independently
• C. Crossing over during mitosis breaks linkages
• D. Genes on different chromosomes do not recombine

Answer: (A)

Independent assortment comes from the way chromosomes behave during meiosis. When the cell forms gametes, homologous chromosomes line up and separate independently of one another. If most genes sit on different chromosomes, each chromosome is sorted into gametes without regard to the others, producing the many allele combinations Mendel observed.

The other ideas don’t fit as well. Genes that are linked on the same chromosome don’t assort independently across generations unless crossing over during meiosis breaks that linkage. Crossing over occurs in meiosis, not mitosis. And saying that genes on different chromosomes do not recombine is misleading; independent assortment describes their separate distribution, while recombination is a distinct process that reshuffles alleles on the same chromosome.