Metafemale

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Metafemale, also called a superfemale, is a rare, low-viability Drosophila (fruit fly) that looks female but has more X chromosomes than its autosome sets. In this system, the normal male has 1 X and 2 sets of autosomes (X:A = 0.5), while a normal female has 2 X and 2 autosomes (X:A = 1.0). A metafemale has more X chromosomes than autosome sets (X:A > 1.0), such as 3 X with 2 autosomes or 4 X with 3 autosomes. The idea comes from the genic balance sex-determination system discovered by Calvin Bridges in 1921 (he used the terms “superfemale” and “supermale”). Curt Stern later introduced the terms “metafemale” and “metamale” in 1959.