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 Cornellās College of Agriculture in 1919. Her research focused on heredity ā 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 kernelsĀ were inherited. Unlike Mendel, she was able to link this to the plantsā 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.
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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 wasnāt until they were discovered in bacteria decades later that McClintockās discoveryĀ got the recognition it deserved. We now know that thereĀ are multiple types of these transposons or ājumping genesā, and that they can be found in large numbers in almost all organisms.
Transposons are often referred to as junk DNA ā the DNA in our genomes that doesnāt directly code for proteins.Ā Some estimates suggestĀ they make up around half the human genome, and as much as 90 per cent of the genome of maize. MostĀ transposons seem to be silentĀ andĀ theyĀ donāt 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 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 orĀ misunderstandingĀ her work. Others have argued that it wasnāt until later on that the far-reaching, genomic implications of her discoveryĀ became clear. We are unlikely to knowĀ for sure until the Nobel archiveĀ makes its McClintock papersĀ 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 thatĀ are not caused by alterations inĀ DNA.Ā She proposed this idea more than 40 years before this concept ā now known as epigenetics ā was formally studied.
