Final answer:
Genes are linearly arranged on chromosomes, and this organization helps to understand their inheritance patterns and genetic linkage. The closer the genes are on the chromosome, the less likely they are to be separated by recombination. Chromosome mapping and the study of linkage have been essential tools in genetic research.
Step-by-step explanation:
Chromosome maps have proved that genes lie in a linear fashion in the chromosome, which is fundamental for understanding genetic inheritance and linkage. The construction of a chromosome map was greatly influenced by the work of Sturtevant, who made various assumptions including that genes were ordered serially on chromosomes and that recombination could occur with equal likelihood anywhere along a chromosome's length. This resulted in the realization that closer alleles tend to be inherited together while those farther apart have a higher chance of recombination.
During the process of meiosis, linked genes on the same chromosome may separate due to crossing-over, which leads to recombination of alleles. The frequency of crossing-over between genes is used to construct linkage maps that show the locations of genes on chromosomes. Through these studies, it was discovered that chromosomes contain hundreds or thousands of genes organized linearly on chromosomes, akin to beads on a string, and that they become highly condensed and visible under a microscope during cell division.