Simplify the following text for a Grade 10 native English-speaking person.
Original: Hermann Joseph Muller ( or H. J. Muller ) ( December 21 , 1890 -- April 5 , 1967 ) was an American geneticist , educator , and Nobel laureate best known for his work on the physiological and genetic effects of radiation ( X-ray mutagenesis ) as well as his outspoken political beliefs .
Simplified: Hermann Joseph Muller , generally known as H.J. Muller , ( 21 December 1890 â `` 5 April 1967 ) was an American geneticist , educator , and Nobel laureate . He was best known for his work on the physiological and genetic effects of radiation , as well as his outspoken political beliefs .