Punnett square showing classic results of T.H. Morgan's experiment revealing that some traits are sex-linked. In the early 1900's T.H. Morgan's experiments with fruit flies confirmed that genes are found on chromosomes and also that some traits are coded for by genes carried on the X chromosome (sex-linked traits). This Punnett square shows the results for his famous F1 cross of red-eyed hybrid females with red-eyed males. the 3:1 ratio of dominant red to recessive white eyes was Mendelian and expected. The surprising result was that - of the white eyed flies all were males (because males carry only one X chromosome and more easily express X-linked recessive traits).