1927
1931
HERMANN J . MULLER
X-rays had been used in clinical medicine and for experimental purposes in physics since their discovery in 1895 . But their value to genetics research only became apparent when Muller , an American geneticist , used radioactivity to produce point mutations in the fruit fly Drosophila . At the time , the prospect that inherited traits could be intentionally changed or controlled - and possibly applied to human beings - provoked widespread awe , admiration , and fear .
BARBARA MCCLINTOCK & HARRIET CREIGHTON
In 1931 , McClintock and her graduate student , Creighton , provided the first experimental proof that genes were physically positioned on chromosomes . Although Thomas Hunt Morgan was the first person credited with suggesting the link between genetic traits and chromosomes , McClintock ' s innovative cytogenetic techniques allowed her to confirm Morgan ' s ideas .
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