The very first edition of Mendel’s Garden, a genetics carnival, is now up at The force that through….
While I’m at it, let me remind everyone that a new Tangled Bank will be appearing at Centrerion on Wednesday—now is the time to send entries to me or [email protected].
Maternal effect genes are a special class of genes that have their effect in the reproductive organs of the mutant; they are interesting because the mutant organism may appear phenotypically normal, and it is the progeny that express detectable differences, and they do so whether the progeny have inherited the mutant gene or not. That sounds a little confusing, but it really isn’t that complex. I’ll explain it using one canonical example of a maternal effect gene, bicoid.
To continue a bit of theme, I mentioned that there were some different ways to approach biology, and that old-school systematists with their breadth of knowledge about the diversity of life are getting harder and harder to find. This is something I also bring up in my introductory biology course, where we discuss how biologists do their work, and I mention that one distinction you can find (which is really a continuum and frequently breached) is that there are bench scientists and field scientists, and they differ in multiple ways. Bench scientists tend to be strongly reductionist, tend to focus on one or very few species, and may study just one specific, highly inbred lab strain of a species, and try to minimize environmental variables. Variation is noise that interferes with getting at basic mechanisms. Field scientists, on the other hand, argue that the simplicity of the lab is unrealistic, that the proper study of organisms has to be done in the messy complexity of the real world, and think that variation, rather than being uninteresting noise, is fascinating stuff, the meat and potatoes of evolution. Both points of view have their place, and speaking for all biologists, I think we appreciate the power and necessity of both approaches. The money seems to mostly go to the bench guys, though, which does unfortunately skew the field as a whole.
The fugu is a famous fish, at least as a Japanese sushi dish containing a potentially lethal neurotoxin that was featured on an episode of The Simpsons. Fugu is a member of the pufferfish group, which have another claim to fame: an extremely small genome, roughly a tenth the size of that of other vertebrates. The genome of several species of pufferfish is being sequenced, and the latest issue of Nature announces the completion of a draft sequence for the green spotted pufferfish, Tetraodon nigroviridis, a small freshwater species.
Last night, I had to read this book RPM mentioned. It’s not very long—about 100 pages, counting a preface, an epilogue, and an afterward, and it has lots of pictures—but be warned: it’s very inside baseball.
The book is Won for All: How the Drosophila Genome Was Sequenced(amzn/b&n/abe/pwll) by Michael Ashburner, and its subject is the rush to sequence the Drosophila genome in 1998-1999. It’s a rather strange twist on what I expected, though. While the subtitle says “How the Drosophila Genome Was Sequenced,” there is almost no science at all in the body of the book; instead, it’s all about the people and the politics, with Ashburner flitting about from place to place, yelling at people and eating sushi. It’s phenomenally entertaining.
Since Evolgen recognizes the importance of evo-devo, I’ll return the favor: bioinformatics is going to be critical to the evo-devo research program, which to date has emphasized the “devo” part with much work on model systems, but is going to put increasing demands on comparative molecular information from genomics and bioinformatics to fulfill the promise of the “evo” part. I’m sitting on a plane flying east, and to pass the time I’ve been reading a very nice review of the concept of modularity in evo-devo by Paula Mabee (also a fish developmental biologist, and also working in a small college in a small town in the midwest…but rather deservedly better known than yours truly). In addition to summarizing the importance of the concept of modularity to evolution and development, the paper also does something I always appreciate: it summarizes the key questions that the modern evo-devo research program is working to answer.
In previous articles about fly development, I’d gone from the maternal gradient to genes that are expressed in alternating stripes (pair-rule genes), and mentioned some genes (the segment polarity genes) that are expressed in every segment. The end result is the development of a segmented animal: one made up of a repeated series of morphological modules, all the same.
Building an animal with repeated elements like that is a wonderfully versatile strategy for making an organism larger without making it too much more complicated, but it’s not the whole story. Just repeating the same bits over and over again is a way to make a generic wormlike thing—a tapeworm, for instance—but even tapeworms may need to specialize certain individual segments for specific functions. At its simplest, it may be necessary to modify one end for feeding, and the opposite end for mating. So now, in addition to staking out the tissues of the embryo as belonging to discrete segments, we also need a mechanism that says “build mouthparts here (and not everywhere)”, and “put genitalia here (not over there)”.
This really is an excellent review of three books in the field of evo-devo—
From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design (amzn/b&n/abe/pwll),
Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom (amzn/b&n/abe/pwll), and
The Plausibility of Life:Resolving Darwin’s Dilemma (amzn/b&n/abe/pwll)—all highly recommended by me and the NY Times. The nice thing about this review, too, is that it gives a short summary of the field and its growing importance.
It’s all about style. When you’re out and about looking for mates, what tends to draw the eye first are general signals—health and vigor, symmetry, absence of blemishes or injuries, that sort of thing—but then we also look for that special something, that je ne sais quoi, that dash of character and fashionable uniqueness. In humans, we see the pursuit of that elusive element in shifting fashions: hairstyles, clothing, and makeup change season by season in our efforts to stand out and catch the eye in subtle ways that do not distract from the more important signals of beauty and health.
Flies do the same thing, exhibiting genetic traits that draw the attention of the opposite sex, and while nowhere near as flighty as the foibles of human fashion, they do exhibit considerable variability. Changes in body pigmentation, courtship rituals, and pheromones are all affected by sexual selection, but one odd feature in particular is the presence of spots on the wing. Flies flash and vibrate their wings at prospective mates, so the presence or absence of wing spots can be a distinctive species-specific element in their evolution. One curious thing is that wing spots seem to be easy to lose and gain in a fly lineage, and species independently generate very similar pigment spots. What is it about these patterns that makes them simultaneously labile and frequently re-expressed?
Here’s what seems to be a relatively simple problem in evolution. Within the Drosophila genus (and in diverse insects in general), species have evolved patterned spots on their wings, which seem to be important in species-specific courtship. Gompel et al. have been exploring in depth one particular problem, illustrated below: how did a spot-free ancestral fly species acquire that distinctive dark patch near the front tip of the wing in Drosophila biarmipes? Their answer involves dissecting the molecular regulators of pattern in the fly wing, doing comparative sequence analyses and identifying the specific stretches of DNA involved in turning on the pigment pattern, and testing their models experimentally by expressing novel gene constructs in different species of flies.
