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Dr Oliver Mayo was interviewed in 2010 for the Interviews with Australian scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge and view science as a human endeavour.
The following summary of Mayo’s career sets the context for the extract chosen for these teachers’ notes. The extract discusses the phenomena of self-incompatibility and Mayo’s use of computer simulations to unravel the dynamics of this system in plants. Use the focus questions that accompany the extract to promote discussion among your students.
Oliver Mayo was born in Adelaide in 1942. Mayo was educated at St Peter’s College and then enrolled in a BSc degree at the University of Adelaide. He completed this degree, with Honours, in 1964. Mayo’s Honour’s year was spent analysing fleece weight in order to choose those sheep for breeding which would increase wool yield. Mayo then began his PhD, again at the University of Adelaide, which he completed in 1968. During his PhD, Mayo used the then new method of computer simulation to model the dynamics of self-incompatibility in plants.
In 1968 Mayo travelled to the University of Edinburgh as a CSIRO senior overseas student at the Institute of Animal Genetics (1968-9) and then a Leckie-Mactier fellow at the Department of Genetics (1969-71). While in Edinburgh Mayo worked on frequency dependent selection of the alleles of alcohol dehydrogenate. Mayo came back to Australia in 1971 and joined the Biometry Section at the Waite Agricultural Research Institute as a senior lecturer (1971-8) and then reader (1979-89). In 1987 he also accepted the position of dean of the Faculty of Agricultural Science at the University of Adelaide. Mayo made the move to Sydney in 1989 to become chief of the CSIRO Division of Animal Production, a position that he held until his retirement in 2000. Upon his retirement, Mayo was made an honorary research fellow of CSIRO Livestock Industries. More recently, Mayo completed a BA from the University of Adelaide majoring in German and Italian (2008).
Mayo has been recognised throughout his career via membership to the Russian Academy of Agricultural Science (1992), fellowship to the Australian Academy of Technological Sciences and Engineering (1994), fellowship to the Australian Academy of Science (1996), awarding of the Centenary Medal (2001), an invitation to deliver the 24th Fisher Memorial Lecture in Edinburgh, UK (2002) and the Knibbs Lecture of the Statistical Society of Australia in Canberra (2003). Mayo has also served on many boards and committees including president of the South Australian branch of the Human Genetics Society of Australia (1979-82), vice president of the Genetics Society of Australia (1991-3) and council member of the Australian Academy of Science (2008-11).
Self incompatibility or ‘don’t breed with yourself’
‘Self-incompatibility’: essentially that means you don’t breed with yourself; is that right?
Exactly. As Darwin spent chapters and chapters showing in the Origin of Species and then wrote large books about, plants and animals tend to perform better when they outcross or outbreed. Mechanisms to ensure outbreeding rather than breeding with oneself have evolved. That is telling it as a ‘just-so story’. But you can show that this is the case: sex is the most obvious and most important single way of ensuring that you don’t breed with yourself. By and large, it’s impossible for animals to do that. There are small exceptions here and there, even in lizards, and they are not that unusual in invertebrates, aphids and things like that, for example. But most animals need to mate with another animal to produce the next generation. That is to unite male gametes or sperm with eggs or ova.
Now, plants have two obvious characteristics to somebody who comes mainly with a statistical background: they don’t get around much any more and they’re green—and these two things are interconnected. But plants have to be able to disperse their pollen, which is the equivalent of semen. And that’s one mechanism: just the dispersal of pollen. But if they dispersed the pollen and yet it would work on the same plant, then you would have self-pollination. This is what you have with peas, and that’s why Mendel was so wise to choose them: they were true breeding because they always pollinated themselves. But self-incompatibility is one of a number of mechanisms that have evolved which ensure outcrossing. The essence of it is that the plant cannot pollinate itself. It also cannot pollinate certain close relations that happen to have the same gene combinations. Many different mechanisms have evolved that are more or less efficient. Some of them will allow more pollination of quite close relations and with others virtually no close relation can be pollinated.
Early on in my PhD, I looked at the dynamics of one of the simplest systems: it’s called ‘gametophytically determined’. This is just a pompous way of saying that a gene that is in a pollen grain is expressed carrying just one copy. Thus the pollen grain a gamete and it has only half the chromosomes. In addition, in the female plant both genes that she’s carrying are expressed in the stigma, which is where the pollen lands to pollinate and fertilise the plant. I worked on the dynamics of this system.
This system had been controversial for many years because Fisher and Wright had disagreed about it—as they had on so much else—but only about the details. When you are as distinguished and crotchety as Fisher was you get these controversies which are blown up out of all proportion. In the case of Wright, I think, he was a nicer man but a little sly. Many other notable population geneticists had worked on it. Warren Ewens had worked on it, he was also from South Australia, a notable Australian geneticist now in human genetics. Also Motoo Kimura, the most notable Japanese population geneticist, had worked on it.
A fellow PhD student, John Sved, perhaps my closest scientific friend, said to me, ‘This looks like a problem you could solve with computer simulation; why don’t you give it a go?’ I said, ‘What’s computer simulation?’ He gave me three papers to read; and my supervisor, Henry Bennett, a very fine population geneticist, gave me another half a dozen. That is all there were in the world at that time using this technique. In this technique, you make a model population in the computer with numbers, randomly breed from this population and follow what it does over many generations. With this, I was able to show that Wright and Fisher were both right—the true answers were in between what they had said, and they were actually pretty close together. And I showed that what some of the other people had said — Warren Ewens and an English geneticist—was not right.
An edited transcript of the full interview can be found at http://www.science.org.au/node/327117.
Focus questions
Select activities that are most appropriate for your lesson plan or add your own. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.
allele
chromosome
computer simulation
gamete
genetics
outbreeding
pollen
self incompatibility
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