Unsung heroes in science: Barbara McClintock

Early life

Born in 1902 in Hartford, Connecticut, USA, Barbara was known as an independent child who was happy to be by herself, traits that stayed with her into adulthood. She had a huge interest in science and was encouraged by her father to go to college, despite her mother’s fears that going to college would make young Barbara ‘unmarriageable’. Barbara received her BSc degree in botany from Cornell’s College of Agriculture in 1923, and went on to receive a PhD in 1927, also in botany. After receiving her PhD, she remained at Cornell, continuing to study the genetics of maize.

Even in the earliest stages of her career, Barbara was making a number of important discoveries about how genes and chromosomes work. One of her pioneering early projects was to develop a stain to see the chromosomes in maize. This helped with understanding how chromosomes behaved, including discovering that some chromosomes are always located near to each other and this means that certain genes are usually inherited together. Along with her student Harriet Creighton, she published a paper in 1931 demonstrating that chromosomes can physically exchange segments of DNA.

As her reputation grew, Barbara worked in a number of different institutions, but despite her talents she had difficulty finding a permanent position as few places allowed women to be professors. She finally managed to gain an assistant professorship at the University of Missouri in 1936 but even then realised that she was unlikely to get promoted. It wasn’t until 1941 that she found a permanent position, at the Department of Genetics at the Carnegie Institution of Washington in Cold Spring Harbour. It was while she was here that she first made the discovery that genes can jump.

Jumping genes in maize

She discovered that this movement of genes could lead to mutations within the chromosome, and this could affect the function of the gene.

Genes are found at particular locations within a chromosome. This genetic location is known as a locus (or loci if you’re talking about lots of them). When studying the leaves of maize plants, Barbara noticed that some of the leaves had different colours and patterns. When she looked at the chromosomes in these leaves, she saw that certain loci in some chromosomes had switched positions. She also investigated maize kernels, which also showed different patterns of colours depending on whether and how these genes had been switched around in the chromosome. She discovered that this movement of genes could lead to mutations within the chromosome, and this could affect the function of the gene. This movement also had a role in switching genes on or off.

This process is known as transposition and genes with the ability to jump are called ‘transposons’ or ‘transposable elements’. Scientists are still not entirely sure why transposition happens, although along with switching genes on and off, the process might help to drive reshuffling of the genome, perhaps creating more genetic diversity and so helping with evolution.

A hostile reception

She was met with ‘puzzlement, even hostility’ from the scientific community.

When Barbara first published and spoke about jumping genes in 1950 and 1951, she was met with ‘puzzlement, even hostility’ from the scientific community. This was because her discovery didn’t fit with what was understood at the time about how genes work. The idea that a gene that could be switched back on after it had been switched off was particularly controversial. The idea at the time was that if a gene was switched off, this was permanent and the gene couldn’t be switched back on again. However, Barbara wasn’t fazed, saying, “It didn’t bother me, I just knew I was right. Anybody who had had that evidence thrown at them with such abandon couldn’t help but come to the conclusions I did about it.”

While people didn’t agree with her on transposons, Barbara’s talent and extraordinary body of work did earn her some personal recognition at the time, including being elected to the National Academy of Sciences at the young age of 42. Eventually, her work on transposons began to receive more recognition as techniques to study genetics improved and other scientists were able to confirm not only that transposons existed, but that they could be found in other organisms as well as maize. Transposons were found in bacteria and bacteriophage viruses, then in fruit flies. Eventually it was confirmed that transposition happens in humans too. It is now thought that around 50% of the human genome is made up of transposons.

While it may seem unfair that Barbara McClinktock didn’t receive as much recognition as some of her peers, it was not something that bothered her in the slightest. In her Nobel Prize statement, she said, “It might seem unfair to reward a person for having so much pleasure, over the years, asking the maize plant to solve specific problems and then watching its responses.”

Article written by Louise Walker, Public Engagement Development Coordinator at Wellcome Connecting Science