Barbara McClintock

Barbara McClintock was a Nobel prize-winning plant geneticist, whose multiple discoveries in maize have changed our understanding of genetics.

Born in Connecticut in 1902, McClintock began studying at Cornell’s College of Agriculture in 1919. Her research focused on heredity – the inheritance of genetic traits in corn, also known as maize. Just as Gregor Mendel had studied how certain features were passed across generations of peas in the mid-nineteenth century, McClintock tracked how characteristics like the colour of maize kernels were inherited. Unlike Mendel, she was able to link this to the plants’ chromosomes.

Most of our DNA is wound-up and stored in discrete volumes called chromosomes, which are housed inside the nucleus of every cell. The DNA of each chromosome encodes our genes in a set sequence, meaning that each gene normally resides at the same physical point along a chromosome. The first experimental proof that genes are positioned on chromosomes came from work McClintock did with Harriet Creighton in the early 1930s.

But during the 1940s and 1950s, McClintock discovered that genetic elements can occasionally move to a different position, a process that can cause genes nearby to become less or more active.

These genetic elements came to be known as transposable elements, but it wasn’t until they were discovered in bacteria decades later that McClintock’s discovery got the recognition it deserved. We now know that there are multiple types of these transposons or “jumping genes”, and that they can be found in large numbers in almost all organisms.

Transposons are often referred to as junk DNA – the DNA in our genomes that doesn’t directly code for proteins. Some estimates suggest they make up around half the human genome, and as much as 90 per cent of the genome of maize. Most transposons seem to be silent and they don’t jump to new positions. Some, however, do jump to new positions from generation to generation, and have the potential to cause harmful mutations when they do so.

McClintock was awarded the 1983 Nobel Prize in Physiology or Medicine for her discovery of mobile genetic elements. Why she was awarded the prize so long after she made this discovery is the subject of some debate. Some have suggested that this was down to sexism or misunderstanding her work. Others have argued that it wasn’t until later on that the far-reaching, genomic implications of her discovery became clear. We are unlikely to know for sure until the Nobel archive makes its McClintock papers publicly accessible in 2033.

In addition to her work on chromosomes and transposable elements, McClintock also speculated that it is possible to inherit changes in gene activity that are not caused by alterations in DNA. She proposed this idea more than 40 years before this concept – now known as epigenetics – was formally studied.