Mechanism to allow for evolution. How did this mechanism come to be?

[Monique]

Most genetic markers as they relate to disease association involve statistical probablilities (if you have such and such allele, you have such and such probablility of contracting such and such disorder). But that said, sure you could have a certain mutation, duplication, or deletion that may result in some disorder, but that gene is most likely just a part of a larger interaction with other genes and probably has multiple functions and forms.

Sure there are multifactorial or polygenic disorders, but there are also mendelian disorders where a single gene is responsible for a specific disease (or trait). Look at Mendel's work on peas or Brenner's work on nematodes for examples of mendelian genetics.

 

[BigFairy]

Thanks for clearing that up.

 

[ViewsofMars]

Here’s something worthy to note from the Journal of Evolutionary Biology, Volume 22 Issue 1, Pages 192 – 200, Nov 11, 2008.

The evolution of sex-determining mechanisms: lessons from temperature-sensitive mutations in sex determination genes in Caenorhabditis elegans

C. H. CHANDLER*, P. C. PHILLIPS† & F. J. JANZEN*
*Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA, USA
†Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR, USA
Abstract:"Sexual reproduction is one of the most taxonomically conserved traits, yet sex-determining mechanisms (SDMs) are quite diverse. For instance, there are numerous forms of environmental sex determination (ESD), in which an organism's sex is determined not by genotype, but by environmental factors during development. Important questions remain regarding transitions between SDMs, in part because the organisms exhibiting unique mechanisms often make difficult study organisms. One potential solution is to utilize mutant strains in model organisms better suited to answering these questions. We have characterized two such strains of the model nematode Caenorhabditis elegans. These strains harbour temperature-sensitive mutations in key sex-determining genes. We show that they display a sex ratio reaction norm in response to rearing temperature similar to other organisms with ESD. Next, we show that these mutations also cause deleterious pleiotropic effects on overall fitness. Finally, we show that these mutations are fundamentally different at the genetic sequence level. These strains will be a useful complement to naturally occurring taxa with ESD in future research examining the molecular basis of and the selective forces driving evolutionary transitions between sex determination mechanisms.”
http://www3.interscience.wiley.com/journal/121510645/abstract?CRETRY=1&SRETRY=0

This also peeked my interest.

Title: Evolution and mechanisms of plant tolerance to flooding stress.
Author: Jackson, Michael B.
Ishizawa, Kimiharu
Ito, Osamu

Found In: Annals of botany. Oxford University Press 2009 Jan., v. 103, no. 2p. 137-142.

Abstract: "BACKGROUND: In recognition of the 200th anniversary of Charles Darwin’s birth, this short article on flooding stress acknowledges not only Darwin’s great contribution to the concept of evolution but also to the study of plant physiology. In modern biology, Darwin-inspired reductionist physiology continues to shed light on mechanisms that confer competitive advantage in many varied and challenging environments, including those where flooding is prevalent. SCOPE: Mild flooding is experienced by most land plants but as its severity increases, fewer species are able to grow and survive. At the extreme, a highly exclusive aquatic lifestyle appears to have evolved numerous times over the past 120 million years. Although only 1-2% of angiosperms are aquatics, some of their adaptive characteristics are also seen in those adopting an amphibious lifestyle where flooding is less frequent. Lowland rice, the staple cereal for much of tropical Asia falls into this category. But, even amongst dry-land dwellers, or certain of their sub-populations, modest tolerance to occasional flooding is to be found, for example in wheat. The collection of papers summarized in this article describes advances to the understanding of mechanisms that explain flooding tolerance in aquatic, amphibious and dry-land plants. Work to develop more tolerant crops or manage flood-prone environments more effectively is also included. The experimental approaches range from molecular analyses, through biochemistry and metabolomics to whole-plant physiology, plant breeding and ecology."
http://agricola.nal.usda.gov/cgi-bi...=20090923120352&SID=1&DB=local&STARTDB=AGRIDB

I'm in the process of comparing the last one to an antique book I picked up entitled AN EVOLUTIONARY SURVEY OF THE PLANT KINGDOM by Robert F. Scagel, Robert J. Bandoni, Glenn E. Rouse, W.B. Scholfield, Janet R. Stein, and T.M.C. Taylor, Wadswroth Publishing Company, Inc. , 1968.