In the Light of Evolution Volume I: Adaptation and Complex Design (2007) / Chapter Skim
Currently Skimming:
Pages 65-82
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 65... ...
Character ization of the components, structures, and operational dynamics of specific genetic networks should lead to a better understanding not only of the morphological traits they underlie but of the biases that influence the directions of evolutionary change. Furthermore, such knowledge may permit assessment of the relative degrees of probability of short evolutionary trajectories, those on the micro evolutionary scale.
|
From page 66... ...
for the near-universality of scale-free networks, but the general importance of networks as organizational devices is undisputed. in biology, an understanding of the structure and dynamics of genetic networks, in particular, is now widely viewed as crucial to understanding phenomena as diverse as metabolic systems, phage developmental switches, protein interaction systems, transcriptional controls, and complex developmental traits.
|
From page 67... ...
however, in general, identifying the elements and bound aries of developmental genetic networks, which underlie morphological traits, is especially difficult (Wilkins, 2007b)
|
From page 68... ...
evolutionary biology, in fact, was founded on a metaphor, ‘‘natural selection,'' which was Darwin's explanation of the evolutionary process by means of a term that leaned on the ways that breeders artificially select and develop new varieties of animals and plants. other, and later, evolutionary metaphors include such figures of speech as ‘‘the adaptive landscape,'' ‘‘the red Queen hypothesis,'' ‘‘the molecular clock,'' and ‘‘Muller's ratchet.'' Two of the most prominent metaphors, however, are those of ‘‘design'' and ‘‘bricolage.'' Design, in fact, figures in the title of the Colloquium from which this article results, and, as Francisco Ayala discusses in this volume (Chapter 1)
|
From page 69... ...
The first is the set of preexisting properties of the recruited molecule, permitting its adoption for new roles. When a transcription factor (TF)
|
From page 70... ...
The crucial point is that the recruitment of modules is made possible by the prior evolutionaryselective history that constructed and optimized performance of the network module. The relevance of these points to organismal evolution is that it is the particular combination of network modules used that determines the composition of the entire genetic network governing a trait (Fig.
|
From page 71... ...
, however, serves as a general indicator of Xing ) , the importance of alterations in domain structure and composition as an input to regulatory change (Alonso and Wilkins, 2005)
|
From page 72... ...
there are not just genes (as in the traditional levels-of-selection argument) but additional levels of genetic–molecular organization, namely genetic networks and their mod ules, that natural selection actively screens.
|
From page 73... ...
; adaptive loss of pelvic armature in freshwater sticklebacks (shapiro et al., 2004; shapiro Colosimo et al., 2004)
|
From page 74... ...
can fully explain the developmental change that lies at the heart of the respective evolutionary change. The still miss ing parts of the explanation, in all of these instances, involve the genetic network of which the respective identified molecule is a part and how that network then regulates selective cell proliferation (and apoptosis in the case of the bat's interdigital webbing)
|
From page 75... ...
single-gene stories, however informative in themselves, cannot provide comparable understanding. For loss of traits, however, as in the stickleback example, knowing the genetic networks responsible for those traits may be unnecessary.
|
From page 76... ...
A detailed knowledge of genetic networks, which necessarily includes an understanding of their component modules, can provide even more: such knowledge provides a platform from which to assess the relative a priori probabilities of certain evolutionary trajectories. such assessment would necessarily be approximate, but even that degree of understanding would be sufficient to allow the beginnings of a predictive approach to evolutionary trajectories, extending the potential range of hypothesis testing in evolutionary biology.
|
From page 77... ...
Between "Design" and "Bricolage" / al., 2002, and stathopoulos and levine, 2005.) yet closer inspection of such .)
|
From page 78... ...
/ Adam S Wilkins FiGUre 4.4 Three kinds of genetic pathways and the effects on their outputs from upstream loss-of-function mutations.
|
From page 79... ...
Given the plethora of networks and morphologies, however, that there are to explore and the costs (in money, time, and sheer hard work) of characterizing developmental genetic networks (Wilkins, 2007b)
|
From page 80... ...
My principal suggestion here is that analyses of the networks or network modules that link developmental patterning mecha nisms to growth and pigmentation patterns could have special importance in understanding the genetic basis of many microevolutionary-scale events. Furthermore, simple calculations involving gene size and mutation rate indicate that even relatively modest-sized genetic networks, found in organisms of moderately sized populations, should harbor significant standing variation of potential phenotype-changing capacity (Wilkins, Wilkins, 2007b)
|
From page 81... ...
The central point of this chapter, however, is that a knowledge of the network modules that constitute particular genetic networks, underlying specific developmental processes in particular organisms (hence, their morphological traits) , can greatly enrich understanding of the ways in which particular genetic changes promote particular developmental changes.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.