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Friday, November 22, 2024

Kostas Kampourakis cautions us against teaching Mendelian genetics

A few weeks ago I put up a post on Were you lied to in your genetics class?. At the time I thought it was just a fringe view being expressed by a graduate student who didn't understand genetics but now I realize that it's much more important than that.

Kostas Kampourakis is a respected scientist who is being promoted by the National Center for Science Education (NCSE) as an excellent communicator of evolution. Here's a short video (below) where he explains why teachers are making a mistake by saying that Mendel is the father of genetics and that simple Mendelian genetics can explain complex traits.

I'm struggling to understand his point. Here's what I think he means.

Kampourakis uses the example of eye color in Drosophila. He agrees that segregation of the allele responsible for eye color may follow the Mendelian rules1 but it's wrong to assume that there's a single gene responsible for eye color in fruit flies. He thinks that the goal is to understand the complexities of development and standard Mendelian genetics gives a completely distorted view of that subject, assuming, of course, that teachers can't separate genetics from understanding development.

Part of the problem is that we use the word "trait" differently. Take Mendel's example of pea color as another example. [Identity of the Product of Mendel's Green Cotyledon Gene (Update)] What Mendel was studying was the segregation of alleles in a gene called sgr (stay-green). It codes for an enzyme involved in the degradation of chlorophyll during senescence. When the enzyme is defective, chlorophyll isn't degraded and one of the visible phenotypes is that peas stay green instead of turning yellow.

I believe that the fundamental trait is the lack of an enzyme for degrading chlorophyll and this is what I would teach my students. I would also show them that the phenotype can be easily explained once you understand the biochemistry. It shows you that the connection between the fundamental trait and the visible phenotype can be mysterious so you should be careful about jumping to conclusions.

I think that Kampourakis sees this differently. He thinks that the example of green vs yellow peas is used to teach students that the color of peas is completely determined by a single gene. He thinks that the "trait" is the develpment of seed color in peas.

Kampourakis believes that "people looking for explanations and whatever happens to them in terms of disease and their own features, they find hard to reconcile the simplistic model that they have been taught with the realities of life." I think what he means is that students are being taught that single genes will always determine complex characteristics. He attributes that to the teaching of Mendelian genetics.

If he is correct, then that kind of teaching has to stop but I don't think it's the fault of Mendelian genetics. Mendelian genetics—indeed the entire field of genetics sensu stricto—is about the segregation of alleles. It is not about development even though we have come to learn a lot about development through genetics and the phenotype of mutants. I think that genetics and development are separate topics.

Kampourakis disagrees. He says, "we need, I think, to teach genetics from a developmental perspective. We need to show that genes do not determine traits but they are implicated in development." I believe this perspective comes from a more fundamental bias that distinguishes his worldview from mine. I tend to see genetics as a subject that covers all of biology and that includes all species such as bacteria, viruses, and single-cell eukaryotes. He tends to see things from a human perspective, which is much more complex than dealing with simple organisms. I think we should concentrate on teaching students about simple well-understood model organisms and then move on to explaining how this applies to more complex organisms. Kampourakis seems to be implying that we should jump right into reaching high school students about the most challenging issues in biology.


1. Actually, the common allele for white eye in Drosophila (see image) is X-linked so it doesn't follow the standard rules for Mendelian segregation!

12 comments :

Argon said...

I suppose we could teach intro to economics without discussing microeconomics....

Stephen Bunnell said...

With you on this, as usual

Joe Felsenstein said...

The idea that there is one gene for eye color, one for earlobe shape, one for this, one for that died in about 1920 as geneticists found more and more examples of pleiotropy. Over the next decade or two quantitative geneticists came to understand that a simple model of determination of traits by adding up effects of alleles was a very useful approximation, even though of course these loci did interact too. In 1917 Sewall Wright published a series of papers reviewing coat color genetics in multiple species, and suggesting that the genes acted by producing enzymes, and that one could explain the interactions by the action of these enzymes in the coal pigment pathways. (I once asked Sewall Wright if he had been the first to suggest that genes produced enzymes, and he said oh no, Cuenot had suggested that in 1904). So Kampurakis is a bit out of date.

Joe Felsenstein said...

Oops: "coal pigment" --> coat color pigment
"Kampurakis" --> Kampourakis

Donald Forsdyke said...

William Bateson began correspondence with the physician Archibald Garrod in January 1902. The latter developed the one-gene-one-enzyme idea in his 1909 text Inborn Errors of Metabolism. In 1934 Garrod noted that "it was Bateson who saw the daylight". For details see p. 195 of "Treasure Your Exceptions." The Science and Life of William Bateson (2nd edition 2022).

Joe Felsenstein said...

It is also worth noting that a common kind of genetic experiment was to make two inbred lines that differed only at one locus (or at two possibly-linked loci). Knowing how Mendelian genetics works is essential to understand the results of crosses in those cases.

SPARC said...

Before Crispr/cas9 was available the need to backcross mouse mutants for 10 generations to end up in a pure genetic background to reduce the effects of other genes. For the very same reasons the Jackson lab does quite some backcrossing to reduce effects cause by genetic drift.

Mehrshad said...

But I'm in favor of the cell -centric view of life not gene-center perspective --supposedly I assume that fellow is emphasising on that view which is more holistic and complete

Nesslig20 said...

Mendelian genetics—indeed the entire field of genetics sensu stricto—is about the segregation of alleles. It is not about development even though we have come to learn a lot about development through genetics and the phenotype of mutants. I think that genetics and development are separate topics.

I completely disagree with this. Genetics as a field came about through through studying the inheritance of physical traits (the phenotype) and explaining how they are passed on. The phenotype was the key starting concept, and the observation that the phenotype was inherited (or sometimes not) across generations was the very subject of genetics from the get-go. There would be not genetics without the phenotype. The only exception I can think of is "pure" population genetics regarding situations were you are only concerned with alleles and their frequency (nothing said about phenotypes in this case). However, that's a far from generalising the entire field of genetics (etiam in stricto sensu). This is especially true regarding Mendelian genetics, the first law of which is the law of dominance, which does not make sense without the phenotype.

So, both genotype and phenotype are key concepts in the study of genetics. The inheritance of the phenotype was the observation to be explained. The passing on of the genotype (alleles) was the explanation. However, the concept of the phenotype is incomplete without ontogeny. The phenotype is produced through ontogeny. One could argue that ontogeny is (part of) the phenotype. Without ontogeny, the connection between the genotype and phenotype becomes a blackbox, and you end up in a situation akin to that classical cartoon "then a miracle occurs".

Joe Felsenstein said...

@Nesslig20: Is this just an argument about names? About what is called "genetics". It seems that it is not about the biology of anything.

Nesslig20 said...

@Joe Felsenstein
No. This is about the facts of history. The inheritance of the phenotype was the phenomenon to be explained, and those interested in answering this question started the field of genetics. However, the inheritance of the phenotype is incomplete without ontogeny. Genetics without development doesn't explain the phenotype, yet it is still commonly believed through notions such as "the genome is the blueprint for the organism".

Larry Moran said...

@Nesslig20 The phenotype is simply a marker for an allele. Genetics explains the segregation of alleles. Biochemistry, molecular biology, and other fields explain the connection between the allele and the phenotype.

Some people think that the field of genetics includes all of the things that explain phenotypes, including transcription and translation. Are you one of those people?