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VOICE ONE:
I’m Doug Johnson.
VOICE TWO:
Barbara McClintock
And I’m Barbara Klein with PEOPLE IN AMERICA in VOA Special English. Today,
we tell about Barbara McClintock. She was one of the most important
scientists of the twentieth century. She made important discoveries about
genes and chromosomes.
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VOICE ONE:
Barbara McClintock was born in nineteen-oh-two in Hartford, Connecticut.
Barbara was the third of four children. Her family moved to the Brooklyn area
of New York City in nineteen-oh-eight. Barbara was an active child with
interests in sports and music. She also developed an interest in science.
She studied science at Cornell University in Ithaca, New York. Barbara was
among a small number of undergraduate students to receive training in
genetics in nineteen twenty-one. Years later, she noted that few college
students wanted to study genetics.
VOICE TWO:
In the early nineteen-twenties, genetics had not received widespread
acceptance as a subject. Only twenty years had passed since scientists re-
discovered the theories of heredity. Gregor Mendel proposed these ideas after
completing a series of experiments with plants. His experiments helped
scientists better understand how genes operate. They showed how genetic
qualities are passed to living things from their ancestors.
VOICE ONE:
Barbara McClintock decided to study botany, the scientific study of plants,
at Cornell University. She completed her undergraduate studies in nineteen
twenty-three. McClintock decided to continue her education at Cornell. She
completed a master’s degree in nineteen twenty-five. Two years later, she
finished all her requirements for a doctorate degree.
In the late nineteen-twenties, McClintock joined several other students in a
group that studied genetics. The students included a future winner of the
Nobel Prize, George Beadle. Another was Marcus Rhoades. Years later, he would
become a leading expert in genetics.
McClintock said both men recognized the importance of exploring the
connection between genes and chromosomes.
McClintock stayed at Cornell after she completed her education. She taught
students botany. She also supervised genetic studies of the corn plant, or
maize. She studied chromosomes, which are lines of genes. She made several
discoveries about genes and chromosomes.
VOICE TWO:
The nineteen thirties were not a good time to be a young scientist in the
United States. The country was in the middle of the great economic
depression. Millions of Americans were unemployed. Male scientists were
offered jobs. But female geneticists were not much in demand.
McClintock received two offers to travel and carry out research projects. The
first came from America’s National Research Council. She worked at several
places, including Cornell and the University of Missouri in Columbia. Later,
a group called the Guggenheim Foundation provided financial aid for her to
study in Germany. McClintock went to Berlin, but returned to Cornell the
following year. Her skills and work were widely praised. But she still was
unable to find a permanent job.
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VOICE ONE:
For years, scientists had been using x-rays to study genetic material in
plants and other organisms. They found that x-rays caused genes to change.
Sometimes, the x-rays physically broke the chromosome. Genetic researchers
looked for changes in the organism. Then they used this information to
produce a map linking the changes to a single area of the chromosome.
McClintock became interested in the way genes reacted to unusual events. She
formed a successful working relationship with Lewis Stadler of the University
of Missouri. He had demonstrated the effects of x-rays on corn.
Stadler sent maize treated with radiation to McClintock. She identified
unusual areas she called ring chromosomes. She believed they were chromosomes
broken by radiation. The broken ends sometimes joined together and formed a
circle, or ring. This led her to believe that a structure at the end of the
chromosome prevents chromosomes from changing. She called this structure the
telomere.
