Genetic Analysis of Evolution in Fruit Flies

Primary Article: Genome-wide analysis of a long-term evolution experiment with Drosophila by Burke, Dunham, Shahrestani, Thorton, Rose, and Long. doi:10.1038/nature09352

Drosophila melanogaster pictured above is the common species of fruit fly typically used as a model organism for the experimental observation of Mendelian inheritance patterns by scientists of all levels across the world. A recent study performed by the department of Ecology and Evolutionary Biology at the University of California Irvine, and the department of Molecular and Computational Biology at the University of Southern California outlined an experiment using D. melanogaster that compiled data obtained from examining the genome of fruit flies that have undergone sustained selection for shortened developmental time for over 600 generations with the genome fruit flies that had no direct selection on developmental time.  The commonly held genetic theory of evolution can be explained in a model of a classic sweep, which holds that there is a change among the nucleotides in the neighboring DNA of a mutation as a result of natural selection, and that the resulting advantageous allele becomes set within a population. However, in this study, the involved scientists noted that the classical sweep model was not followed, but instead presented a model for the genetic variation caused by selective breeding, which held that a population generally reached a new phenotypic optimum before beneficial mutations have had time to become fixed. The overall conclusion of this study was that selective breeding across 600 generations of fruit flies did not lead to the fixation of newly arising unconditionally advantageous alleles, and that selection doesn’t readily expunge the genetic variation in sexual populations. This study provides evidence against the classically held model of genetic sweeps, whether through a series of small sweeps involving single nucleotide polymorphisms or through classic sweeps in which one advantageous allele becomes fixed within a population. The results of this study were that there was an absence of actual mutations at the genetic level that allowed for the lessened developmental time of the flies selected for shorter developmental time, and that the flies were somehow able to better use the vast array of developmental genes that they already possessed for short term developmental superiority.

This study is a good example of the overall theme that genetics students will come to learn and appreciate, that genetics is much like real life. If you can think of a situation where something might exist, you will most likely be able to find an example of it, often in contradiction to classically held “textbook” type models.