One of the first aneuploids to be recognized was a fruit fly with a single X chromosome and no Y chromosome, discovered by Calvin Bridges in 1913. Another early study of aneuploidy focused on mutants in the Jimson weed (Datura stramonium). A. Francis Blakeslee began breeding this plant in 1913, and he observed that crosses with several Jimson-weed mutants produced unusual ratios of progeny. For example, the globe mutation (which produces a globe-shaped seedcase) was dominant, but was inherited primarily from the female parent. When globe mutants self-fertilized, only 25% of the progeny had the globe phenotype. If the globe mutation were strictly dominant, Blakeslee should have seen 75% of the progeny with the trait, so the 25% that he observed was unsual. Blakeslee isolated 12 different mutants that exhibited peculiar patterns of inheritance.
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