The Cost of Acquiring Crossveinless-ness in Waddington’s Assimilation - The Cost of Acquiring Crossveinless-ness in Waddington’s Assimilation - Open Access Pub

Neo-Darwinian natural selection theory indicates that sudden, drastic changes in the environment place selective pressure on genetic variants in a population. As time progresses, this pressure sculpts individuals to better fit this new environment. Waddington’s classic experiment was repeated using white-eyed (the w1118strains) flies which produced the crossveinless (cve; disturbed wing crossveins) trait from the parent generation. The F1 generation was split into two selection lines: an Upward Selection Line, that produced more cve in successive generations, and a Downward Selection Line that responded with a consistent but non-linear decline in the percentage of crossveinless. This article will introduce and enlarge observations made on flies with cve; especially the manner in which the Waddington experiment impacts the population. It seems that Waddington evaluated crossveinless just by what it is good for, but not by the price of using it. That is to say, there is an inevitable cost that needs to be paid in order to acquire crossveinless-ness (cve and the associated phenotypes). DOI10.14302/issn.2576-6694.jbbs-17-1748 No matter how drastic and sudden, a change in the environment does not bring a change in genetics. Such changes add constraint, by way of increased selective pressure, on those few, rare, genetic variants in the population. It is the repeated nature of selection, with time, that changes the gene frequency in favor of the most suitable individuals. This continues to the point that the whole population comprises more of these fitter variants than the older, less fit wild stock. Waddington’s Genetic Assimilation theory 1 is perhaps an extension to this concept, whereby repeated artificial selection under stress leads to an acquired trait becoming fixed in a population. In 1953, he showed that Drosophila melanogaster (wild-type) flies that were heat-shocked produced a Crossveinless (disrupted posterior crossveins) trait. Through repeated selection of this trait with heat-shock, he not only increased its frequency in the population, but also found that individuals, from the untreated stock, showed the phenotype. However, when it comes to the selection of crossveinless, the repeated selection results in the production of less fit individuals in successive generations. One of the key points about the Natural Selection theory is that nature only favors what is good or beneficial. Crossveinless offers no selective advantage to the heat-shocked flies. Fly Stocks Two strains of Drosophilamelanogaster were used in the experiment: the wild-type