Polytene pairings of paracentric inversion polymorphisms in Drosophila pseudobscura:
 Dobzhansky et al. (1937 ~ 1975)
"The Genetics of Natural Populations," I - XLIII

    Some of the first studies of the importance of genetics in evolution were performed by Theodosius Dobzhansky (1900 - 1975) on Drosophila pseudobscura fruit flies of southwestern North America. Where Giemsa banding patterns on the giant salivary gland chromosomes of flies are readily visualized, Dobzhansky showed that different geographic populations of D. pseudobscura had undergone paracentric inversion of specific chromosomal segments with respect to the Standard karyotype. When genetic crosses between these populations were made, Dobzhansky showed that the expected inversion loops formed between the chromosomes.

    Because the heterozygous chromosome combinations were less fertile, the paracentric inversions served as reproductive barriers between populations, which allowed them to develop local genetic adaptations. For example, Dobzhansky showed that certain chromosomal types varied regularly with altitude and temperature. Such chromosome differences also exist between closely-related species in the genus Drosophila, thus showing the continuity of within- and between-species genetic variation.

    Dobzhansky's 1942 book "Genetics and the Origins of Species" is considered one of the foundations of the Modern Synthesis in evolutionary biology  .

Figure ©2002 by Griffiths et al.; all text material ©2014 by Steven M. Carr