Tales from the Teaching Lab: Early misconceptions in genetics

When I started this blog, it was supposed to be a news blog: me getting to grips with and explaining new papers that I found interesting. Recently I’ve been thoroughly uninspired, but trying not to resort to writing more opinion pieces about how to survive Grad school (even if that does seem to be what I do best).

Nevertheless, it’s been over 2 weeks since my last post, and while demonstrating yesterday, a familiar itch beginning to niggle. Whereas in previous years I’ve done a more-than-normal amount of tutoring and demonstrating, this year I’ve only covering a small handful of lab classes, one of which is Introductory Genetics. The class is pretty simple. Students are given a variety of mutant Arabidopsis that they have to phenotype, in addition to the F1 and F2 of back crosses to the wild type and crosses between mutants. They are trying to find out whether the mutations are single gene traits; dominants or recessive; and whether multiple mutants are caused by mutations in the same or different lines.

This is the third year I have demonstrated for this class, and the previous year I marked the open book exam that students take at the end, without having demonstrated for the practical, so I’m probably more familiar with the class than anybody except for the professor teaching it. Along the way I have had to do a fair amount of mental gymnastics, but I’ve also picked up on a few of the most common misconceptions that students hold. I actually clearly remember as a first year undergraduate being confused by the term “wild type” because nobody had explained to me that this was a technological term for the working copy of a gene: I thought it meant the type of gene that animals had in the wild. Which is fine, until you start thinking about mouse or Drosophila genetics! 

I often think that our students are too spoon-fed, but at the same time they seem to miss out on a few fairly vital pieces of information that would make their lives so much easier. Here’s my list:

– Wild type means the genotype/phenotype of a species as it naturally occurs (i.e. before any mutation or outbreeding). Where more than one allele commonly occurs, the one at the highest frequency is generally called wild type.

– All mutants in breeding experiments will be true-breeding (i.e. homozygous). When an interesting mutant is found, it is selfed for generations until we are confident that it has two mutant copies of the gene.

– If we describe a mutation as being ‘recessive’, that’s short hand for ‘recessive to the wild type’: it’s not like with colouring alleles where you might have four different possibilities that have a hierarchy of dominance. A mutant will only be thought about relative to the wildtype in the first instance.

– If a plant is a “mutant”, that actually means it has one mutated gene. It’s not like X-men where if you’re a mutant then you’re completely messed up. So if you cross mutant A (aa) with mutant B (bb) then both of those plants also have wild type copies of every other gene (i.e. aaBB x AAbb or if you were being really precise aaBBCCDD AAbbCCDD etc)

– If you are talking about multiple genes then all of your genotypes must contain the alleles of every gene. You can’t cross centipede and sonic and have a genotype nomenclature system of cen cen x son son. (Or you probably could, but 90% of students will end up confused).

– While I’m at it, before you utter the words “This is an Arabidopsis mutant.” Pick up a pot of Arabidopsis and show them. Every year I get around 25% of students calling their newly-named-gene-and-alleles ARAB, arab-1 and arab-2. 

And finally, a plea to lecturers: when teaching genetics, be nice to your students. Pick (or make up!) genes that start with A, B, D, H, N, Q, R, T. If you use genes where the upper and lower-cases look the same (or are even similar – E is fine for some students, but for others terrible) then when they try to abbreviate the gene to a single letter you will lose the ability to tell the difference between dominant and recessive and all hell will break loose!


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