How and Why Chromosome Inversions Evolve

Alfred Sturtevant, who invented genetic mapping while still an undergraduate, published the first evidence of a chromosomal inversion in 1921 He suggested then, and later proved, that they have a dramatic effect on transmission: when heterozygous, inversions suppress recombination. Over the next half century, inspired largely by Dobzhansky and his coworkers, much of empirical population genetics devoted itself to studying the abundant polymorphisms within and fixed differences of inversions between species of Drosophila Starting in the 1970s, this rich literature largely sank from view with the rise of biochemical and then molecular genetics. But inversions are ascendant again. Comparative genomics is now revealing that chromosomes are far more structurally fluid than even Dobzhansky dared to suppose. Where classic cytogenetics identified only nine inversions that distinguish humans and chimpanzees, comparison of their genomic sequences reveals on the order of 1,500 3 (Figure Despite the importance of inversions as a major mechanism for reorganizing the genome, we are still struggling to understand how and why they evolve almost a century after Sturtevant's discovery.