Speciation in Drosophila
Evolution of dominance
Genetics of speciation:
My research focuses on the role of genetic conflict in the evolution of intrinsic postzygotic isolation. Recent studies have identified several genes that cause hybrid sterility or inviability; several of these evolve rapidly. However, the evolutionary forces that drive the rapid changes in these genes remain unclear. The idea that intra-genomic conflict may cause the evolution of hybrid sterility is intuitively appealing, but empirical evidence has been scant. “Sterile” F1 hybrid males between the USA and Bogotá subspecies of Drosophila pseudoobscura become very weakly fertile when aged and produce all daughters, reflecting sex chromosome segregation distortion. My work involves identifying the hybrid segregation distorter and hybrid sterility genes and testing the idea that normally suppressed segregation distortion within species gets unmasked in the hybrids to cause sterility.
Evolution of dominance:
The dominance of deleterious mutations has important consequences for phenomena such as inbreeding depression, the evolution of diploidy, and levels of natural genetic variation. Kacser and Burns' metabolic theory provides a paradigmatic explanation for why most large-effect mutations are recessive. According to the metabolic theory, the recessivity of large-effect mutations is an inevitable consequence of a diminishing-returns relationship between flux through a metabolic pathway and enzymatic activity at any step in the pathway. Using data on gene deletions in yeast, I showed that a negative correlation between homozygous effects and dominance of mutations exists for all major categories of genes analyzed, not just those encoding enzymes. My findings show that Kacser and Burns’s theory, in it present form, cannot provide complete explanation of dominance.
Phadnis, N. and Orr, H.A. 2008. A single gene causes both male sterility and segregation distortion in Drosophila hybrids. Science, accepted.
Orr, H.A., Masly, J.P & Phadnis, N. 2006. Speciation in Drosophila: from genes to molecules. Journal of Heredity 2007 98(2):103-110
Phadnis, N. & Fry, J.D. 2005. Widespread Correlations between Dominance and Homozygous Effects of Mutations: Implications for Theories of Dominance. Genetics 2005 171: 385-392 .
Fry, J.D., C.M. Bahnck, M. Mikucki, N. Phadnis and W.C. Slattery. 2004 Dietary ethanol mediates selection on aldehyde dehydrogenese activity in Drosophila melanogaster. Integrative and Comparative Biology 44:275-283.
Watve, M., V. Shejval, C. Sonawane, M. Rahalkar, A. Matapurkar, Y. Shouche, M. Patole, N. Phadnis, and 5 other authors 2000 The ‘K’ selected oligophilic bacteria: a key to uncultured diversity? Current Science 78:1535-1542.