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Corn plants in a field
Harvested corn
McClintock decided to become a geneticist. A geneticist is a scientist
who studies how traits are passed on from one
generation
of an
organism to the next. McClintock spent most of her time studying the
traits of corn. She studied the color, size, and texture of corn. She grew
fields of corn and studied the corn kernels (seeds). By studying the
kernels, she could tell what traits were passed from one generation to
the next through the corn’s seeds.
In 1931, McClintock made an important discovery. Scientists already
knew that every living thing passes genetic messages to its
offspring
.
These messages control what the offspring look like. These messages are
called
genes
. Genes are carried by structures called
chromosomes
.
Scientists thought a gene located on a certain chromosome would
always be there.
McClintock discovered that this was not true. Her experiments
showed that genes could cross over, or move, from one chromosome to
another. Crossing over meant that a greater variety of traits could exist.
She published the first genetic map for corn.
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