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A summary statement from a 1922 journal article entitled "Sex Ratio and Unisexual Sterility in Hybrid Animals" reads as follows:

“When in the F1 offspring of a cross between two animal species or races one sex is absent, rare, or sterile, that sex is always the heterozygous sex.”

This phenomenon later became known as


Hardy-Weinberg equilibrium.


Fisher’s principle.


Wright's shifting balance theory of evolution.


Haldane’s rule.

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