Barbara McClintock
Smithsonian Institution Archives
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鈥檚 College of Agriculture in 1919. Her research focused on heredity 鈥 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聽were inherited. Unlike Mendel, she was able to link this to the plants鈥 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.
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These genetic elements came to be known as transposable elements, but it wasn鈥檛 until they were discovered in bacteria decades later that McClintock鈥檚 discovery聽got the recognition it deserved. We now know that there聽are multiple types of these transposons or 鈥渏umping genes鈥, and that they can be found in large numbers in almost all organisms.
Transposons are often referred to as junk DNA 鈥 the DNA in our genomes that doesn鈥檛 directly code for proteins.聽Some estimates suggest聽they make up around half the human genome, and as much as 90 per cent of the genome of maize. Most聽transposons seem to be silent聽and聽they聽don鈥檛 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 or聽misunderstanding聽her work. Others have argued that it wasn鈥檛 until later on that the far-reaching, genomic implications of her discovery聽became clear. We are unlikely to know聽for sure until the Nobel archive聽makes its McClintock papers聽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聽are not caused by alterations in聽DNA.聽She proposed this idea more than 40 years before this concept 鈥 now known as epigenetics 鈥 was formally studied.
