Question: what's your favourite experiment?

Andy MacLeod answered on 23 Jun 2011:

I like the work of Thomas Hunt Morgan on fruit flies.

Hi simonic. I don’t really do “experiments” myself in the way some scientists do. I analyse data, I test hypotheses, but I don’t do any lab-work myself. But I am a geneticist, and there have been some really neat experiments in the history of that subject.

We all owe something to Gregor Mendel, the 19th century monk who first identified the principles of heredity based on observing pea plants in his monastery’s garden. But some of my favourite genetics experiments come from an American geneticist called Thomas Hunt Morgan, who worked in the early 20th century.

Morgan was among the first to fruit flies as an experimental organism. They have some advantages for this – they have a very short generation time, and many flies can be made at each tep. That means it’s pretty likely that some will have mutations in their DNA that cause visible changes in the fly. You can track these changes through generation if you have a good enough eye, and a lot of patience.

Morgan tried to create his own mutations. Using chemicals and radiation, he changed the DNA of some of the flies to create changes that could be followed. Many of these traits followed the laws that Mendel had outlined a few decades earlier, but there were some patterns that couldn’t be explained. Some traits seemed to be “linked”. So that sometimes, two mutations were found together in the same flies more often than would have predicted. They weren’t entirely independent, violating Mendel’s second law.

Morgan and colleagues studied the inheritance patterns of lots of different traits, and found that they fell into a number of cateogories – “linkage groups”. They also found out that it was likely that the genes were arranged in a linear oder. We now know these linkage groups correspond to chromosomes, and one of Morgan’s students used these observations to create the first genetic map, that showed the order of genes along a chromosome.

A lot of my work involves mapping genes to specific locations on chromosomes. “Linkage analysis” is still widely used to locate and identify genes that are inherited together on the same chromosome. The unit we use to measure how far apart genes are is called the Morgan. 😀