The laws of inheritance

14 August 2019

Interview with 

Greg Radick, University of Leeds


Illustration of a pea plant


The story goes that Mendel was ahead of his time in some way - a visionary genius, unappreciated during his life. But if that’s true, then where does someone like that come from? Genius surely can’t spring from thin air. To learn more, Phil Sansom talked to historian Greg Radick...

Greg - Mendel was born in 1822. His parents were not-very-well-to-do farmers. And it quickly became apparent that Johann, as he was called, was very gifted intellectually - marked out to do something special. So in 1843 Mendel enters the monastery, and he went on to study at the University of Vienna. So we sometimes have this picture of Mendel as the monk in the garden; and that's deeply misleading, because he had about as good a scientific education as you could receive.

Phil - He goes back to the monastery with this fantastic training and decides he wants to undertake a study on plant hybrids, and what happens to traits like the colours of the flowers or the seeds.

Greg - And where Mendel went beyond his predecessors is that he spent two years making sure that for example, when he had a yellow-seeded pea, that its progeny only ever produced yellow-seeded peas; that is to say, it was ‘true breeding’. So purified his stocks, and then upon crossing he counted. And again this was a break with his predecessors. No-one had ever done this, certainly not at the scale that Mendel did.

Phil - So this was one of his smart moves: taking these ideas about rigour from the physical sciences he learnt at the University of Vienna, and for the first time applying them to plant breeding. He kept records. He repeated experiments. He used controls.

Greg - He carried on these studies for about eight years, and in 1865 he gave a couple of lectures to the Brünn Natural Sciences Society about what he discovered. Brünn itself is something like the Leeds or Manchester of Central Europe, it's an industrial powerhouse. Mendel’s in this fantastic environment...

Phil - And his results are really well received. The crux is this pattern that Xander was talking about, that when you cross a true-breeding plant with yellow peas to one with green peas, the kids are all yellow, and the grandkids are - on average - three yellow to one green.

Greg - And he called the yellow character the dominant character. By contrast the green character, which disappeared in that first generation but then reappeared, he called the recessive character. So Mendel finds this new pattern. But he goes on then to explain it.

Phil - His theory is that when reproducing, a plant could only pass on either greenness or yellowness, but never a mixture of the two. What we now call his Law of Segregation. In his paper he followed through the maths, the probabilities of what would happen if his theory was true. And the maths showed exactly what his experiments found. A 3:1 ratio of yellow to green.

Greg - So a new pattern is discovered and the new explanation is offered.

Phil - He even extends his theory to more complex ideas. What if you have two traits you’re dealing with? Three? Well, he found each trait is inherited independently of what’s going on with the others. What we now call his Law of Independent Assortment.

Greg - So it’s altogether quite an amazing paper. And then Mendel is elected abbot of his monastery. At that point his scientific studies more or less come to an end and he gets used up in administration. Which seems like a tragedy for science, but as far as we can tell for Mendel it seemed to have been quite a good move. He always had health problems, nervous breakdowns we would call them now, from time to time; all of that seems to go away when he becomes abbot. And he dies in 1884, a respected member of the community, and not especially well known. But then in 1900, quite suddenly, he goes from being pretty obscure to being someone that a lot of people are talking about.


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