Thomas Hunt Morgan's Discoveries:
Thomas Hunt Morgan, through his experiments with the fruit fly Drosophila melanogaster, discovered the phenomenon of sex-linked inheritance, notably in the context of the white-eyed mutation in fruit flies. This finding appeared to violate Mendel's principles, particularly concerning the notion that traits assort independently and that they can be inherited regardless of sex.
Morgan's Explanation:
Morgan explained his findings by proposing the theory of gene linkage. He observed that certain traits were inherited together more often than would be expected if genes were assorted independently, suggesting that these genes were located close to each other on the same chromosome. Specifically, he demonstrated that the white eye color trait was linked to the X chromosome, indicating that inheritance patterns could not be explained solely by Mendel's laws of independent assortment, as these traits seemed to be co-inherited based on their proximity on the chromosome.
Alfred Sturtevant and Gene Mapping:
Alfred Sturtevant, a student of Morgan, took the next step in harnessing the concept of gene linkage to create the first chromosome maps. Sturtevant used the frequency of recombination between linked genes to estimate their distances on a chromosome. By conducting crosses of fruit flies and analyzing the offspring for various combinations of traits, he was able to observe how often recombination occurred. The frequency of recombination between two genes is proportional to the physical distance between them; genes that are closer together tend to be inherited together more frequently than those that are further apart.
From this analysis, he created a genetic map that indicated the relative positions of genes on a chromosome, expressed in map units (centimorgans), which reflected the likelihood of recombination occurring. This revolutionary approach allowed for a systematic method of mapping genes based on their linkage relationships, laying the groundwork for modern genetics and the understanding of chromosome structure and function.