Members of the same chromosome pairs (autosomes) that undergo crossing over during meiosis are called what?

• A. Homologous chromosomes
• B. Sister chromatids
• C. Chromosome
• D. Alleles

Answer: (A)

Homologous chromosomes are the paired chromosomes in a diploid organism, one from each parent, that carry the same genes in the same order. During meiosis, these pairs align and crossing over occurs between their non-sister chromatids, meaning the chromatids that belong to different homologs, not the identical copies on the same chromosome. This exchange of genetic material between homologous chromosomes creates new combinations of alleles and increases genetic diversity in gametes. The other terms don’t fit because sister chromatids are the two identical copies of a chromosome tied at the centromere and do not define the paired chromosomes themselves; a chromosome is a single DNA molecule with its associated proteins; and alleles are the different versions of a gene, not the chromosomes that pair up.