Classes are over, and that means I have more time to think…about my classes. So I’m on the lookout for ideas to improve my teaching, and gosh, look, Nature has an article on better ways to teach genetics. So I read it eagerly, and was left scratching my head. It’s a short news article, so it’s a bit thin on the details of how to teach genetics the way it recommends, but I’m also confused about how this approach would be useful.
The author, Gregory Radick, advocates teaching Weldonian genetics, rather than Mendelian genetics.
In a recent two-year project, we taught university students a curriculum that was altered to reflect what genetics textbooks might be like now if biology circa 1906 had taken the Weldonian rather than the Mendelian route. These students encountered genetics as fundamentally tied to development and environment. Genes were not presented to them as what inheritance is ‘really about’, with everything else relegated to ignorable supporting roles. For example, they were taught that although genes can affect the heart directly, they also affect blood pressure, the body’s activity levels and other influential factors, themselves often influenced by non-genetic factors (such as smoking). Where in this tangle, we ask them, is a gene for heart disease? In effect, this revised curriculum seeks to take what is peripheral in the existing teaching of genetics and make it central, and to make what is central peripheral.
More developmental and environmental influences? That sounds good to me. I already try to get some of that across in my course, but standard transmission genetics is the core concept, and I work hard to make sure they grasp that before we grapple with the complications.
But still, he’s promoting the idea that we roll back our understanding of genetics to 1906, and start fresh from there? That’s just weird. Somebody is maybe a little too infatuated with WFR Weldon, and wants to resume the Genetics Wars of the 1900s (which wasn’t as awesome as my title makes it sound, all steampunkish and ferocious — it was more of an academic argument). Shortly after the rediscovery of Mendel’s work in 1900, a heated debate arose in the literature.
On one side was William Bateson, who was really keen on Mendel. Bateson was predisposed to favor the guy’s method: in 1899, he wrote a prescription for a scientific approach to crack the problem of heredity that was practically a literal description of what Mendel had already done.
What we first require is to know what happens when a variety is crossed with its nearest allies. If the result is to have a scientific value, it is almost absolutely necessary that the offspring of such crossing should then be examined statistically. It must be recorded how many of the offspring resembled each parent and how many showed the characters intermediate between those of its parents. If the parents differ in several characters the offspring must be examined statistically, and marshalled, as it is called, in respect of each of those characters separately.
And then Mendel’s paper from 1865 was unearthed, and that’s exactly what he had done, and he had come up with several general rules of inheritance that could then be applied and tested. Bateson maybe got a little over-enthusiastic, and used Mendel’s result to argue for saltationism, the idea that evolution proceeded in sudden leaps. This side of the Genetics Wars was called the Saltationists, or the Mendelians.
The other side was the Biometricians, led by Weldon, Karl Pearson, and Francis Galton. They objected to Mendel’s genetics for a couple of reasons: it was way too simple to explain everything (they were right), that characters aren’t as discrete as Mendel suggested (they were also right), and that you needed to emphasize statistical analyses more (wha…? I know, really strange, since Mendel’s work was tediously statistical, and Bateson kept emphasizing the importance of statistical analyses).
Weldon’s 1902 paper criticizing Mendelism is actually historically interesting and he does bring up a number of important scientific points. But I wouldn’t use it in an introductory genetics class, because it would just confuse matters and I’m most interested in getting students to understand the practical answers. For instance, it starts with a summary of Mendel’s laws, and then as an objection, raises an argument built around a rudimentary understanding of population genetics (it’s good for 1902, not so good for any time afterwards). He points out that if you take the results of a hybrid cross, which will produce one pure breeding type for every two hybrids and every one of the other pure breeding type, and then produce many generations by selfing (no further hybridizing allowed), the frequency of they hybrids will steadily decrease, because purebreds will only produce purebreds, and hybrids will produce half hybrids and half purebreds of the two types.
It’s trivially true, but not particularly interesting because of the artificially limited nature of crosses after the first generation, and it’s also completely irrelevant to Mendel’s conclusions. It even uses Mendel’s rules to generate the frequency of different combinations in each generation, so it can hardly be used to argue against Mendel. It is an interesting early step in the development of population genetics, I guess.
Weldon then criticizes Mendel for something I think we’re all familiar with: his results were too good to be true! He expected 3:1 ratios, and he got almost exactly 3:1 ratios in all of his published results, and statistically, Weldon points out that this is degree of correspondence is unlikely.
These results then accord so remarkably with Mendel’s summary of them that if they were repeated a second time, under similar conditions and on a similar scale, the chance that the agreement between observation and hypothesis would be worse than that actually obtained is about 16 to 1.
This is also true, but rather petty, and illustrating a flaw in the Biometrician’s approach. Nowadays, ideally, if we saw such a potentially damaging flaw in a core conclusion of a relatively easily replicated experiment, we’d repeat it, especially given that the rest of the paper is an intimately familiar discussion of the properties of a great many varieties of peas. But, to be mean about it, the biometrician’s specialty was statistical analyses of other people’s experiments. (Whew, I can be catty about someone who has been dead for 110 years. Impressive).
But still, the remaining chunk of the paper is much more interesting, in a dry sort of way, then the first part. He looks at peas of a great many readily available varieties, and find that seed color and shape, for instance, exhibit a much greater diversity than the pairs of contrasting traits Mendel analyzed. It’s clear that phenotype is much more complex than the simple binaries Mendel placed them in — and in today’s world where simplistic binary thinking seems to have become the standard cultural mode, that’s a valuable contribution. He also reviews the experiments with various crosses that were going on at the time, and finds that not all traits are passed on with that simple dominant/recessive relationship Mendel documented.
These facts show first that Mendel’s law of dominance conspicuously fails for crosses between certain races, while it appears to hold for others; and secondly that the intensity of a character in one generation of a race is no trustworthy measure of its dominance in hybrids.
(Do I need to remind everyone that a hundred years ago “race” was used in a broad and generic way for what we’d now call “varieties”?)
So I’m left wondering what “Weldonian genetics” I’m supposed to teach. I think I already do. We didn’t just throw everything Weldon mentioned in the trash bucket once he died, but incorporated it into our understanding of inheritance.
The thing is, I spend the first two weeks of my course teaching the history of genetics and reviewing basic Mendelian inheritance. Most of them come out of high school understanding dominant/recessive/simple monohybrid crosses, but I try to make sure they’ve got those simple quantitative relationships down cold. The important thing here is that Mendel enables us to give a quantitative foundation for understanding inheritance, and I’d be curious to know if Radick’s curriculum accomplishes that.
The rest of the semester is spent ripping up the simplifications. We talk about multiple alleles, codominance, epistasis, background effects, conditional alleles, expressivity and penetrance, etc., etc., etc., all the mechanisms that generate the complexity that Weldon appreciated so much, and that Mendel neglected in his simplifications. The Genetics Wars dribbled away because with greater understanding came the awareness that both sides were right, and Bateson and Weldon are rather easily reconciled now. I don’t understand the point of resurrecting an antique enmity when modern genetics is a synthesis.
I also honor Weldon in the lab. The very first lab of the semester is all about statistics and probability, and one of the exercises involves throwing dice a hundred times. I suppose if I wanted to really teach Weldonian genetics, I ought to have each of them throw 12 dice 26,306 times and then analyze the statistics of the distribution. Of course, then we waste the rest of the semester breeding flies, when we could have done more dice throwing, or read other people’s genetics papers and dissected their data tables. I think one Weldonian lab is enough.
One other thing I have to point out about Radick’s experiment in teaching: it doesn’t seem to have been appropriately designed.
Our experimental group consisted of second-year humanities undergraduates. First-year biologists, who were taught the conventional approach, acted as our control.
Whoa. I’m going to say right there is a huge flaw: these two groups are very different populations of students, with different backgrounds, and the goals of those two classes are going to be very different. You can’t compare them adequately, much less claim the first year biologists are a “control”. I’m also wondering where these classes fit into their overall curriculum. We give our first year biology majors a brief overview of genetics in a class that also puts it into context and discusses the philosophy of science and evolution, but it is not a substitute for a full course in genetics. We only give them that in a third year course, after they got some cell biology and statistics under their belt, because first year students here are generally not ready for such an intensely quantitative course (some of our third- and fourth-years aren’t, either).
One last objection, and then I’ll stop muttering over this paper. Radick suggests that Weldon’s death in 1906 was responsible for the ultimate ‘defeat’ of the Biometricians, and even the wikipedia article on Weldon says the same thing. I don’t buy it. There are better reasons for the triumph of the Mendelians, and they are the series of positive results that followed on. I would point to the too-often neglected work of Walter Sutton, who linked abstract Mendelian “unit factors” to the behavior of chromosomes, and made a mathemical concept a biological reality. I’d also suggest that we can’t overlook the power of TH Morgan’s work on Drosophila. Even had Weldon lived, there would have been no change in the course of the science.