Modern genetics arose 150 years ago when Augustinian monk Gregor Mendel (1822-1884) elucidated genetic inheritance in peas, discovering parents pass on heritable factors that we now call genes to offspring.
In 1956 James Watson and Francis Crick discovered genetic information is encoded in DNA molecules (genes) that are transferred from generation to generation. These genes are carried on long strings called chromosomes in the nucleus of the cell.
These are the best-known milestones in genetics but along the way Barbara McClintock (1902-1992) uncovered several critically important natural mechanisms for transporting genetic information, mechanisms so unexpected that they were initially rejected by the wider scientific community – as outlined by Barbara Pfeffer Billauer in an American Council on Science and Health publication earlier this year.
McClintock was elected to the National Academy of Sciences in 1944 and in 1983 was awarded the Nobel Prize in Physiology or Medicine for discovering these mechanisms; the only woman ever to win an unshared Nobel Prize in that category.
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Born Eleanor McClintock in 1902 in Hartford Connecticut, she was the third of four children born to homeopathic physician Thomas McClintock and Sara McClintock. Her parents changed her first name to Barbara to reflect her fiercely independent character. She described this character as her “capacity to be alone”. She went to Cornell University School of Agriculture in 1919, graduating with a BSc in Botany (1921), MSc (1925) and PhD in Botany (1927).
McClintock was considered unsuitable for a teaching career and she worked as a lone researcher most of her professional life. This didn’t bother her at all. It suited for personality and facilitated her capacity to focus on problems with unremitting tenacity.
Working first at Cornell then at Cold Spring Harbor, she studied the new field of cytogenetics in maize, focusing on ways to visualise and characterise maize chromosomes. She described the morphology of the 10 maize chromosomes for the first time and linked chromosome groups of traits that are inherited together.
The importance of McClintock’s work was finally recognised in the 1960s-1970s when her results were replicated by others
Most people with brown eyes have dark hair. The genes for brown hair and dark eyes are on the same chromosome and are inherited together. But some people have blue eyes and dark hair. This phenomenon was not understood until McClintock proved in the 1950s that chromosomes can exchange genes with each other (gene crossover). The long chromosomes can recombine with each other and genes for hair and eye colour can get separated and switched – the gene for brown hair is now inherited with the gene for blue eyes.
McClintock discovered “transposons”, also called “jumping genes”, in the 1940s-1950s. Transposons are segments of DNA that can move throughout the genome. Eukaryotic cells, including human cells, contain large numbers of transposons. These jumping genes act as regulators. Transposon can switch other genes on and off, move about a chromosome or even jump from one chromosome to another.
In 1951, McClintock published work showing that genetic expression relies on extra – chromosomal influences, including transposons. This questioned the conventional wisdom that all inherited traits are governed by fixed chromosomal genes and mystified colleagues, who rebuffed her work. She published her proposal again in 1956, but was rebuffed again. She stopped publishing. But she continued her research, going on after she retired in 1967 until her death in 1992. When awarded the Nobel Prize in 1983, she was still a lone researcher in Cold Spring Harbor.
The importance of McClintock’s work was finally recognised in the 1960s-1970s when her results were replicated by others. Why her work was not accepted initially is unclear. Perhaps there was resistance to accepting such radical results from a woman, perhaps it was resistance to her unorthodox approach to devising hypotheses.
Like Einstein before her McClintock relied a lot on a very vivid imagination which she supplemented with intensely hard work. She is now generally thought to have been on the autism spectrum, awkward in her social relations, had no family to facilitate networking and she had no famous champion such as some other famous female scientists had – for example, Einstein called the German female mathematician Emmy Noether (1882-1935) “a creative mathematical genius”.
McClintock was awkward and very direct in her manner and had something of a reputation as a troublesome eccentric. And she was also an incandescent genius.
William Reville is an emeritus professor of biochemistry at UCC