An easy genetics quiz

I said I had to compose a simple quiz on Mendelian genetics today, and here it is. I’m drug-addled right now, so I couldn’t handle anything at all complicated, so you’ll probably laugh at how basic it is. My philosophy with these quizzes is that I just want to make sure they understand the fundamentals, and later (like next week) I give them something more challenging, and this quiz basically summarizes Mendel’s principles.

Being doped to the gills right now just guarantees that I won’t hit them with anything too tricky or difficult.

Briefly summarize Mendel’s first postulate, and explain under what conditions it fails.

Briefly summarize Mendel’s second postulate, and explain under what conditions it fails.

Briefly summarize Mendel’s third postulate, and explain under what conditions it fails.

Briefly summarize Mendel’s fourth postulate, and explain under what conditions it fails.

If you cross true-breeding vestigial winged, brick red eyed flies to true-breeding long winged scarlet eyed flies, what will the F1 progeny look like?
a. vestigial winged, scarlet eyed
b. long winged, scarlet eyed
c. vestigial winged, brick red eyed
d. long winged, brick red eyed
e. none of the above

What will the genotype of the progeny be?
a. vg+ st+
b. vg- st-
c. vg-vg- st-st-
d. vg+vg- st+st-
e. none of the above

If you cross the F1 progeny to each other, what proportion (0-1.0) of the F2s will have long wings?

If you cross the F1s to each other, what proportion (0-1.0) of the F2s will have scarlet eyes?

What proportion (0-1.0) of the F2s will have long wings AND scarlet eyes?

If you do a backcross, crossing a vestigial winged, scarlet eyed F2 to one of its F1 parents, what proportion (1-1.0) of the progeny will be long winged and brick red eyed?

In pea plants, white flowers (w) are recessive to violet flowers (W), constricted pods (c) are recessive to full pods (C), dwarf (d) is recessive to tall (D), and yellow pods (y) are recessive to green pods (Y). In your garden, you have some true breeding pea plants that are tall, white flowered, with full green pods, and another set of true breedings plants that are dwarf and violet flowered, with constricted yellow pods. By some whim of fashion, your friends would like some dwarf white flowered plants with full yellow pods.

You do a cross of your available plants. What will the progeny look like?
a. Tall white flowered with full green pods
b. Dwarf violet flowered with constricted yellow pods
c. Tall violet flowered with full green pods
d. Dwarf white flowered with constricted yellow pods
e. none of the above

None of the F1s meet your friends’ criteria. If you cross the F1s to each other, though, what proportion of the progeny will be dwarf white flowered plants with full yellow pods?

You have 10 friends. How many F2 seeds will you have to collect and grow to adulthood to find a perfect plant for each one?

Then you have a clever idea. What if you backcrossed the F1s to your existing stock of dwarf and violet flowered, with constricted yellow pods? What would be the frequency of dwarf white flowered plants with full yellow pods be in that cross?

At the end of your gardening exercise, you conclude that
a. that was easy! I should volunteer to do more gardening for my friends!
b. maybe I need to get less picky friends

Today in Genetics class

The lesson for today includes an introduction to pedigree analysis. You all know the conventions of a human pedigree, right?

I also include an addendum.

Genetics science is gradually catching up and recognizing that trans people exist, although there is still some confusion about precisely how to acknowledge them.

Why is genetics hard?

First day back in the classroom, teaching genetics, and I speculate for a bit about why so many people find the subject difficult. I’ve had smart students who struggled with the concepts. I think the answer is that many people don’t get the whole idea of chance and probability and the statistical nature of inheritance.

The autofocus on my camera was a bit goofy. Someday I’ll get this all figured out.

Does anyone object to invading Hitler’s privacy?

I don’t.

When Hitler blew his brains out in the bunker, he splattered the upholstery with blood. An American soldier cut out a swatch of bloody cloth and kept it as a morbid souvenir, eventually donating it to a museum, and recently, geneticists sequenced the sample. Guess what they found?

Most of the interpretations were ambiguous, but they did find one specific abnormality in his genome.

The research is due to be published in a scientific journal, but the key finding is this: Hitler had Kallmann syndrome, a genetic disorder that hinders the normal progression of puberty and the development of sexual organs. Derogatory songs from the war about Hitler’s anatomy may have been meant in jest but, it transpires, they were not just accurate but probably did not go far enough.

A 1923 medical examination of Hitler, which was uncovered in 2015, showed that the Nazi leader did indeed have an undescended testicle but, while we do not know exactly how it manifested, Hitler’s newly discovered genetic condition would have also affected his testosterone levels. It means he had a one in ten chance of having a micropenis. This is suggested by stories from the First World War, where Hitler was bullied over the size of his genitalia.

The genetic finding, while definitive, can only allow for speculation in terms of its impact on Hitler. However, it seems likely that he would have struggled to form sexual relationships, and one historian believes this could prove critical in our understanding of Hitler’s rise to power.

Speculation. That’s an important word. There’s only a limited set of conclusions one can draw from the genetics…but hey, some people are going to go wild with it.

Alex J Kay, a historian at the University of Potsdam, who specialises in Nazi Germany and is a key authority in the documentary, said: “This would help to explain Hitler’s highly unusual and almost complete devotion to politics in his life to the almost complete exclusion of any kind of private life.

“Other senior Nazis had wives, children, even extramarital affairs. Hitler is the one person among the whole Nazi leadership who doesn’t. Therefore, I think that only under Hitler could the Nazi movement have come to power.”

Ugh. No. Those are some sweeping conclusions to draw from a genetic sequence. The geneticists seem to be well aware of the limitations of their analysis, but fortunately for their sensational documentary, they managed to find an irresponsible historian to draw excessive conclusions.

I’m not mad at Sydney Sweeney. I’m just disappointed that this is the only genetics education most people will get

Sydney Sweeney has an ad for American Eagle, in which she simply buttons up a pair of genes in, I guess, a sultry way, while delivering a genetics lesson. It’s kind of a half-assed lesson.

Genes are passed down from parents to offspring, often determining traits like hair color, personality and even eye color.

OK, but it implies a simplistic pattern of inheritance, and worse, uses the word “determining”. “Affects,” or “modulates,” or “contributes to” would be better — there are at least 16 critical genes behind eye color, with maybe 150 genes that can effect the expression of color. Eugenicists a century ago tried to claim that that it was regulated by a simple Mendelian dominant/recessive relationship of a few alleles, but that idea fell apart pretty fast. All you have to do is look at the range of colors in the human population to see it can’t be that simple. Anyone who has a basic understanding of genetics is going to see the flaws in that line.

I’m not going to try to guess how many genes are involved in “personality.” All of them? With a huge contribution from environment and experience.

But then the ad company makes it even worse.

“My jeans are blue,” Sweeney concludes, with the ad delivering the now-infamous line, “Sydney Sweeney has ‘good jeans.’”

Oh god, are they like 12? Conflating ‘jeans’ with ‘genes’ is one of the oldest ‘jokes’ around — I teach genetics, and that word game is so tired and weak, especially since there aren’t even any good jokes built around it (if you know of any, tell me in the comments and I’ll judge the quality of your humor.) I groaned when I heard it. It doesn’t even rise to the level of a dad joke.

This, I thought, is the level of understanding the American public has of genetics.

I guess when I teach genetics this Spring I’m going to have to flop down on the floor with my shirt unbuttoned and slowly fasten up my pants. That’ll get their attention.

When genetics teaching goes very, very bad

Sometimes, when you’re teaching simple Mendelian genetics you have to make up fictitious scenarios, because real genetics is significantly more complicated than introductory students can handle. It’s an approach with pitfalls, though, because you don’t want students to think they can use your toy examples to model reality. There’s also a history of bad genetics misapplied to imply that genetics is reducible to pairs of alleles with only dominant and recessive relationships. I’ve invented simple Mendelian models for my classes, but I usually do something like make a story problem with Martians to avoid any confusion with reality.

But then, some genetics teachers, like Alex Nguyen of Luther Burbank High School invent story problems with a) imaginary human traits, b) traits that correspond to racist stereotypes, and c) assign them to specific, named students in the school. That’s not only misleading, it’s unethical. It’s shamefully bad pedagogy.

Here are some sample questions he actually used in a genetics test. These questions were so bad that a student quickly reported it to the school administration, and within ten minutes the principal showed up to confiscate the exam. And Nguyen tried to continue the test by projecting the questions on an overhead projector! I guess he didn’t get the message.

In high school, there are individuals who are cross-eyed like (the name of a student) and (another name of a student), which is a dominant trait. We call those individuals ‘weirdoes.’ So, if you crossed two weirdoes (the two students named again), that are heterozygous for being cross-eyed, what is the offspring that would result?

Crossed eyes are not a strongly heritable trait, and calling students “weirdos”?

For some reason, the African American culture has influenced most of the student body. How? In African Americans, they have a gene for the pimp walk, which is dominant. What is the result if you cross (student name) homozygous dominant Latina with a homozygous recessive Hmong like (student name)?

“Pimp walk” is not a heritable trait, the Hmong don’t have an unusual walk, and why is he tying this to a Latina student?

Here at the wonderful school of LBHS, we have certain students who love to sleep in class,” the question said. “I even see students fall asleep during exams! Can you believe that?! I don’t like it when students sleep in class… it’s rude! So, WAKE THE #$%K UP! Well, through much study, I have concluded that the gene for falling asleep is dominant. Not only that some students sleep, they snore in class. This too is a dominant trait. What are the possible offspring if you cross a homozygous sleeping, heterozygous snoring student (student name) with a homozygous attentive, non-snoring (student name) student?

Oh god. Do I need to say it? These are not heritable traits.

Human heredity can be very complicated when dealing with SO many traits. Luckily for you, the most that we have dealt with are two trait combinations. Every person on earth has certain body and shapes and this includes their facial structure. Some people have an oval facial structure like (student name) and other people can have a round face like (student name) while others may exhibit a square facial structure like (student name). That is why we make so many different shapes and sizes of glasses. While focusing on facial struct, we also have to consider people’s heights. There are tall people like (student name), mediaum and short people. Determine all possible offspring when (student name) RrTt person is crossed with an (student name) rrTT person.

Well, good for him for introducing dihybrid traits, but things like the shape of the face are polygenic, and not reducible to a simple Mendelian allele, and height has a huge environmental component.

Alex Nguyen was swiftly placed on administrative leave, and replaced with a substitute the next day. The “investigation” continues, but I don’t see why — they’ve caught him red-handed, they’ve got the exam he distributed, they should just fire him for racism and incompetence. And he’s been teaching for over a decade? That tells me there is something deeply wrong about the teaching of genetics in public schools.

My genetics class is going ‘woke’!

I’ve been teaching the students all this basic transmission genetics all semester, and while it’s important and fundamental, it can have a bad effect on people’s brains. I cringe when I hear people talking about human traits using simple Mendelian terms like “dominant” and “recessive” because, while it works for many things, for others it misleads and is overly simplistic. I want my students to come away from the class knowing that genetics is complex and subtle and everything is polygenic and epistasis matters, and that’s hard to do when they’re trying to figure out the basics of doing a fly cross.

It’s also a problem because instilling only the basics of Mendel is a good way to make Nazis — it’s easy to distort simple concepts they barely understand into props for your biases. I’d like to forestall that. Also, I’m in Minnesota, and Minnesota has a smug white people problem.

“The racism you see in Minnesota is the type of racism where people say there is no racism. The only race is the human race,” Myers [not me, no relation] said. “How can we say the only race is the human race when all the people with dark skin are people with higher unemployment rates, dying from COVID, more likely to be arrested, more likely to be beaten by police and murdered? How does that happen when there’s no race?”

So I’m going to wake up all the smart students in my class. My strategy involves handing them a digital folder full of articles from science journals as well as newspapers, telling them to pick one, and present it to the class (I’m sure not going to just lecture on these things — I want students to think about them.) They’re getting the folder today, have to pick an article by Wednesday, and are going to prepare a ten minute summary and review for two weeks from today. It’s going to be fun, right?

Here’s a list of just the titles they have to choose from:

A framework for enhancing ethical genomic research with Indigenous communities (2018)
A review of the Hispanic paradox: time to spill the beans? (2014)
Addressing Racism in Human Genetics and Genomics Education (2022)
Can We Cure Genetic Diseases Without Slipping Into Eugenics? (2015)
Eugenics and scientific racism, (2023)
Genetic Essentialism: On the Deceptive Determinism of DNA (2011)
Genetic Evaluation for Hereditary Cancer Syndromes Among African Americans: A Critical Review (2022)
How to fight racism using science (2020).
Implications of biogeography of human populations for ‘race’ and medicine(2004)
National Academies calls for transforming use of racial and ethnic labels in genetics research (2023)
Population genetics, history, and health patterns in Native Americans (2004).
Race and Genetics: Somber History, Troubled Present (2020)
The apportionment of human diversity, (1972)
Using Population Descriptors in Genetics and Genomics Research (2023)
Women’s Brains, Gould (1980)

It’s an eclectic mix of sources, since I’m trying to capture a range of interests and abilities.

By the way, I do warn them that Lewontin’s “The apportionment of human diversity” is an important classic paper, but not for the faint of heart — it’ll be a challenge for even the most advanced students in the class. Some students love a challenge, though.

Famous person found to have ordinary genetic history

It’s only about 200 years old, pulling a DNA sequence out of a hair sample is a piece of cake. So Beethoven’s DNA has been sequenced. He even gave permission!

In 1802, German composer Ludwig van Beethoven wrote a heart-wrenching letter to his brothers, describing the deafness that forced him to “live like an exile” and yearn for death. Beethoven kept going for another 25 years, propelled by his music, but he begged them to have his hearing loss studied and publicized, so that “so far as possible, the world may be reconciled to me after my death.”

Two centuries later, a team of international researchers has answered that plea by sequencing Beethoven’s DNA, preserved in locks of his hair that collaborators and fans collected as treasured keepsakes.

The central ailment of Beethoven’s life was his hearing loss, which began in his mid-20s. He also suffered from debilitating gastrointestinal symptoms and attacks of jaundice. An autopsy revealed that he had cirrhosis of the liver, pancreatitis and a swollen spleen. Medical biographers have debated what killed him and whether his liver disease was the result of excessive drinking or some other cause.

There are limits to what you can do with DNA. They found no genetic evidence for his hearing loss. They did find signs of a susceptibility to liver disease, and that he had hepatitis B. There is absolutely no indication of a genetic source for his musical talent. I’d go so far as to say it is silly to select a 19th century person for a genetic analysis on the basis of musical ability, which is mostly going to be due to circumstance, rather than intrinsic nature (there may be exceptions, like the heritability of perfect pitch, but even that is pretty wobbly.

They did discover something that ol’ Ludwig Van would not have anticipated and probably wouldn’t want advertized.

The analysis also yielded a surprise: Beethoven’s Y chromosome didn’t match those from living relatives. The common relative they all share was Aert van Beethoven, who lived in the 16th century. Somewhere in the seven generations between Aert and Ludwig van Beethoven, a woman in the family tree had a child with an unknown man, and Beethoven seems to be a descendant of that pairing.

We’ve probably all got evidence of ancestral indiscretions in our genes, though, so that shouldn’t reflect on Beethoven, or on his unidentified female ancestor.