Alison Woollard: Gregor Mendel - the man, the myth, the legend

"Click here to listen to the full podcast episode"

Alison Woollard: Gregor Mendel - the man, the myth, the legend 

She set the scene by taking us all the way back to the earliest days of the science of heredity, with ancient Greek doctor Hippocrates suggesting that the reproductive material was collected together from all parts of the body and handed down to the offspring - explaining why parents look like their children. 

50 years later, the philosopher Aristotle took issue with this, as he couldn’t see how temporary and changeable characteristics like voices and hairstyles could possibly be inherited. This led him to the idea that the bits that contribute to reproduction are somehow siphoned off within the body, foreshadowing the knowledge we have today about how the germline - the cells that make egg and sperm - are separated from the rest of the body early on in development in many species. 

Importantly, these ideas about the nature of heredity held that the male was the one who contributed all the ‘stuff’ while the female was nothing more than a handy incubator - ideas that remained virtually unchanged for more than two millennia.

By the time Mendel was born in July 1822 in the small village of Heinzendorf in what was Austrian Silesia – now the Czech Republic - researchers such as Thomas Knight and John Goss in England were already starting to experiment with breeding various types of peas to see how their characteristics were transmitted down the generations. 

Peas were a handy plant to study, because they had easily measurable and distinct differences in several traits, such as flower colour, height, and the colour and wrinkliness of the seeds. But while these researchers carried out detailed experiments, none of them made the conceptual breakthroughs that Mendel did in his work, outlining the fundamental laws of inheritance that underpin the science of genetics as we know if today.  

We’re not going to go over the science and the story of Mendel’s pea experiments, as many people (including this podcast) have covered it in detail already  - there are some links in the show notes to follow if you’re interested.

Instead, I caught up with Alison after her lecture to chat about some of the less well-known aspects of Mendel’s life and work. I started by asking her what we know of Mendel as a person, over and above his interest in peas.

Alison: You know, it is really difficult to say because there's really not much of a historical record on Mendel's personality or interactions with others and so on and so forth. But I think one thing I would say is that I suspect he was a very anxious person, very nervous, because he did suffer from some sort of nervous conditions.

Alison: And so he was ill during exams and things like that. And I think he also was very worried about how some of his ideas might be perceived amongst the more doctrinally religious members of his order. 

Kat: Because of course he was a friar and it's a bit odd that a man of God should also be a man of science at the time, or was that something that was encouraged?

Alison: Well, it was really important that he was a friar and not a monk because at the time, in his monastery, the friars were encouraged to take part in the community. So a lot of them were teachers and so on. And in his monastery a lot of the friars were doing academic work. So they were very interested in secular academic problems in ideas of the universe, of hybridisation in plants, agriculture, all sorts of things that they were very involved in.

Alison: And so the milieu in which he became part of when he went to the monastery in Brno was a very sort of intellectually rigorous one. 

Kat: What I really liked about your talk as well is, you talked about his work with the peas and it also seemed that he got to do a lot of that science because he couldn't become a teacher.

Alison: Yeah, exactly. So there's this kind of horrible thing that people sometimes say in universities, those who can, do; those who can't, teach. Of course, this is complete nonsense, because good teachers tend to be people that really understand the science and have done a lot of it. But in Mendel's case, it's certainly the case that it was seemed to be those who could, taught and those who couldn't, did research. Which is quite interesting.

Alison: Because he kept failing or not turning up for his exams to make him an accredited teacher. And that gave him more time to do his research. 

Kat: Yeah. It's an interesting picture you have this idea of the friar in his monastery doing all this science and then this other picture thats like, oh, I've gotta do my physics teacher exams.

Oh no, I can't do that. Oh no. Oh, I've just gotta go back to, maybe that was his happy place was in the garden. Just him and his peas. 

Alison: Mm, definitely. Yeah. Yeah. Yeah. Especially at the time when the monastery was sort of being investigated by a group, 

Kat: The church police. 

Alison: Yeah. The church police. Exactly. And I think he probably thought, you know, keep my head down in the greenhouse.

Alison: That's gonna be the best way to go. Don't say anything too controversial. Don't write anything too controversial. And that's probably why he worked on plants and not animals. 

Kat: Bit sexy animals, so it's a bit, ohhh 

Alison: yeah, yeah. A bit too much maybe, and plants less controversial, less about us. And so that was probably it.

Alison: And also the fact that he came from farming families. So I think he was really interested in the application of the science that he was interested in. Could he get better varieties of crops, for example, and things like that. 

Kat: So we've told on the podcast, the story about Mendel and his peas and his crosses and this is a very well worn story.

Kat: You take purple peas and white peas and you cross 'em together. Oh, look, they're all purple. Why is that? That's very strange. But what I hadn't realized, and this is a complete revelation to me, was what you talked about, about a more fundamental observation. So unpack that a bit. So where do we start with this observation of Mendel's?

Alison: There was a lot of debate at the time around what fertilisation involved. And a lot of people thought that it was all to do with the paternal parent. 

Kat: The male. 

Alison: The male, funnily enough, no surprises. Right. And that the female contribution is probably a sort of nurse.

Kat: The sort of seed and soil thing isn't it. It's like the woman is the soil and the man is the seed that actually provides the info for the baby. 

Alison: Yeah. So the idea was the germ cell or what we'd now call the egg, the plant egg cell. Is the sort of nurse. The pollen, the male cell is the thing that actually produces all the content for the next generation.

Alison: So there was a debate. And so whether it's paternal like that, or whether it's biparental both parents being involved. And there was an argument between Fenzl who was a botanist at the time together with Mendel's boss in Vienna. He worked under this guy called Unger. 

Alison: And I think that was in Mendel's mind. He was very interested in this problem. And so he set about trying to work out how many pollen grains you need to fertilize an egg, because there was an idea from Darwin that you needed at least three. 

Kat: Okay. 

Alison: And this work was done by one of Darwin's associates who worked on the four o'clock plant because it had really big pollen grains so it was a really good experimental system. 

Alison: And Mendel sort of revisited those experiments and did some really careful work taking pollen grains from different phenotypes of plants, different color flowers, and showing that only one of those pollen grains is required. So you have one contribution from the pollen and one contribution from the nurse cell, from the egg cell, and so you need both. 

Kat: And crucially that kind of worked if you think about the colors, say you have this idea, say a purple plant is the dominant plant. So you have a purple male plant and then you get purple plants, but he did it the other way around didn't he? 

Kat: He took one single pollen grain from a white plant, or a plant with no colour, and then the female plant had the colour and then all the offspring have that colour. So that really proved that It's female and male parts together. 

Alison: Yeah. That's exactly right. Whichever way he did the cross, he got the same results. And Mendel realised that that was telling him something really, really important.

Kat: It takes two. 

Alison: Exactly. It takes two. And his quote is actually that "the fundamental evidence for the complete union of the contents of both cells lies in the universally confirmed experience, that it is unimportant for the form of the hybrid, which of the original forms was the seed or the pollen plant."

Alison: And it turns out that he thought that this was one of his most important contributions to biology. Although, of course we all just think of the three to one and the nine to three to three to one, all of that stuff was important too, but he thought that this was absolutely crucial. 

Kat: So today in the year 2022, and today we're celebrating Mendel's 200th birthday. We've had some very nice Pimm’s, very nice cake. What place does Mendel have really in the world of modern Genetics today, as you'd see it.

Alison: I think geneticists, it's really important and useful to really engage with Mendel's papers. Because I think there's richness there. I mean, some of the things we've just talked about are not the things that are always represented in the textbooks. 

Alison: But of course the other thing is to look at the things that don't follow Mendel's rules and laws, because they reveal some really rich exceptions that tell us so much about how heredity works, how different bits of biology work. One of them would be, the exception to crosses working the same whichever way around you do them is of course, when you have cytoplasmic inheritance of organelles, like the mitochondria, they always go through the female line through the egg. Those sorts of exceptions can tell us really, really important things about biology.

Kat: And of course our two joint Mendel award winners today, Azim Surani, my old boss, and Davor Solter talking about the phenomenon of genomic imprinting, where you have; The sperm comes from the male, the egg comes from the female, they should come with matching half sets of DNA, but actually some genes are only active if they come from mum and some genes are only active if they come from dad, there's a lot out there. 

Alison: Mm, absolutely. Yeah, really, really fascinating stuff. 

Alison: So when Mendel was asked by his colleagues and associates at the time, why he thought his work had sort of gone kind of unnoticed in many ways. He had lots of answers to that, but one of them was he, he said my time will come. And I would say that his time has most certainly come now. And the next 200 years will reveal even more extraordinary ideas about the nature of heredity and the biological world. So, Go Mendel!

Links:

• https://geneticsunzipped.com/transcripts/2019/1/31/fifty-shades-of-peas

• https://geneticsunzipped.com/transcripts/2019/5/23/bringing-mendel-to-britain 

• https://www.khanacademy.org/science/ap-biology/heredity/mendelian-genetics-ap/a/mendel-and-his-peas 

• https://www.nature.com/scitable/topicpage/gregor-mendel-and-the-principles-of-inheritance-593