Friday, November 05, 2010

Introductory Genetics ≠ Introduction to Genetic Analysis

(The ideas in this post aren't well-organized - I'm still struggling to sort them out.)

I'm finally doing what I should have done ages ago - reading the Prefaces to genetics textbooks.  This is where the authors explain what they are trying to accomplish - what the book is trying to teach.

Reading the Preface to the genetics text always used at UBC (Introduction to Genetic Analysis) clarifies why I think it's wrongheaded.  The goal is to teach students how to do genetic analysis, i.e. how to use genetic methods to find out about biological processes.  (Duh, I shouldn't be surprised, that's what the title says too.)

The framework of IGA has always been explicitly historical, which is (or at least was) sensible. Students of course need to learn how inheritance works before they can use genetic analysis, and in this framework they're taught this by learning about the classic genetic-analysis experiments that were used to discover the mechanisms of inheritance.  By seeing what was learned about inheritance from generations of geneticists studying the results of crosses, students learn both the principles of inheritance and the methods of genetic analysis.

Because this textbook has been so successful (it's now heading for the 10th edition, 35 years after the first), all the other genetics textbooks have adopted its historical Mendel-first framework even when teaching genetic analysis is not the main goal (or only one of them).

But the role of genetics has changed. Genetics is no longer a specialist topic, taught to the best and the brightest students, used by elite biologists.  Rather it's everywhere in our lives - the media (every day, in both discussions of genetics and in analogies ("the DNA of music", "the DNA of advertising"), the doctor's office, the elementary schools.  And genetic analysis itself relies much less on crosses, and more on combinations of mutant-construction, DNA analysis and phenotype analyses.  All of these are more easily taught outside of the context of crosses.

Given this, I think that the primary goal of a modern introductory genetics course shouldn't be to teach genetic analysis, but to give a solid understanding of how inheritance works and how it applies to a broad range of important issues.  

Unfortunately, for most students, this goal isn't achieved by courses that emphasize genetic analysis, especially with the standard historical approach.   One problem is that the students have changed.  Now most biology programs require a course in genetics, so the student base is much broader and more diverse.  Their background has also changed. They've already been taught about DNA and Mendel's 'rules'.  But I think the biggest problem is that the historical approach makes understanding the basic principles more difficult than it needs to be.  Early in the history of genetics, genes were a 'black box', and researchers used genetic analysis to gradually pry the box open.  Now the box is wide open, but we still start teaching it as a black box.  This encourages students to treat genetics principles as factoids to be memorized and regurgitated.

I'm also reading the Preface to Sturtevant and Beadle's 1939 Introduction to Genetics.  They don't take a historical approach at all, rather they have chosen 'to give a natural order that simplifies the presentation.'  They start with chromosomes, introducing sex chromosomes as explaining why there are equal numbers of males and females, and then follow a sex-linked mutation (bar) through crosses where the mutation is either present on the male's sole X or on both of the females Xs.  Because bar+ is NOT dominant to bar-, the phenotypes make sense (the heterozygous genotype gives an intermediate phenotype).  In a later cross using the sex-linked white locus they introduce dominance, and make the point that dominance is a relationship between alleles (they say that w+ is dominant to w-). They also introduce human pedigrees quite early.  Surprisingly, autosomal inheritance and Mendel's work aren't introduced until Chapter III, after Chapter II has discussed sex-linked inheritance and the segregation of chromosomes in meiosis.

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