Advanced Placement (AP) Biology Practice Exam

Homologous chromosomes share the same sequence of genes, which is the reason that option B is the correct answer. Each homologous chromosome pair consists of one chromosome inherited from the mother and one from the father that carry genes for the same traits in the same order. However, while they have the same genes at the same loci, they may carry different alleles, which are versions of those genes. Other aspects, such as having the same number of chromosomes, is true for any diploid organism, as they all have pairs of homologous chromosomes—this does not specifically define what is shared between homologs. The presence of the same alleles is not guaranteed, as homologous chromosomes can differ at certain loci—this is where genetic variation comes into play. Lastly, the origin of chromosomes from the same parent is not applicable to homologous chromosomes collectively, since one chromosome comes from each parent, not the same one. Thus, the unique factor that homologous chromosomes have in common is their gene sequences.