Slide showing a diagram concerning X and Y chromosomes. Slide shows a diagram concerning X and Y chromosomes. There are three rows of equations. The first reads: 'P1 red [female] x white [male] white [female] x red [male].' The second reads: 'F1 red [two females] + red [two males] red [two females] + red [two males]'. The third reads: 'F2 2 red [females] : 1 red [male] : 1 white [female] 1 red [female] : 1 white [female] : 2 red [males]'. Text below diagram reads: 'Let R = red and r = white, since red is dominant, and assume that the factors are borne in both X- and Y- chromosomes. The analysis works out as follows:'. Late 19th to early 20th century