Final answer:
Knowledge about chromosomes explains variation by influencing genetic diversity through crossing over, random chromosome assortment, and fertilization in sexual reproduction. Mutations provide an additional source of variation, constantly offering new genetic combinations for selection.
Step-by-step explanation:
Knowledge about the structure and function of chromosomes explains variation in sexually reproducing organisms primarily by influencing genetic diversity. In sexually reproducing organisms, each individual receives two copies of each gene, one from each parent, in the form of alleles. Different combinations of these alleles account for the variation in characteristics of organisms. Sexual reproduction has three main processes that contribute to variation among offspring, which are crossing over, random chromosome assortment during meiosis, and fertilization. Together, these processes result in offspring that are genetically unique compared to their parents and siblings.
Moreover, genetic mutations, which are changes in DNA, provide a fundamental source of new genetic variation. In sexually reproducing organisms, these mutations are continually remixed, allowing for a vast array of potential genetic combinations in successive generations. The importance of this variation is evident by the prevalence of sexual reproduction to the survival and reproduction of a population in a changing environment.