In the first generation only one of each pair of con- 

 trasted or mated characters appeared. Such was termed 

 the dominant character. In the next generation, the hy- 

 brids being self-fertilized, there occurred a splitting or se- 

 gregation into the original characters according to a definite 

 ratio. For example, when a yellow-seeded variety was 

 crossed with a green-seeded variety, the hybrids were all 

 yellow-seeded — yellow being dominant and green recessive. 

 When the yellow-seeded hybrids were self-fertilized, the 

 progeny consisted of 75 per cent, yellow seeds, and 25 per 

 cent, green seeds. The green-seeded plants, however, when 

 self-fertilized, produced green seeds entirely, hence were 

 pure; but when the yellow-seeded plants, were self- fertilized 

 some of the progeny produced yellow and green seeds, while 

 others produced yellow seeds only. 



The results may be shown diagrammatically as follows: 



Yellow X Greep. P 



Yellow (impure) Fi 



I 



I i I 



25% Yellow (pure) 50% \ellow (impure) 25% Green (pure) . .F2 



etc. 

 \ 



The gametic matings in the " selfing " for the F"., genera- 

 tion may be represented as follows when it is borne in mind 

 that in fertilization there will be two kinds of gametes and 

 these in equal numbers: 



Y G = male gametes in equal 



Female gametes f Y YY YG I numbers 



in \ = YY-|-2YG-fGG 



equal numbers ( G YG GG ' 



Where YY is a pure yellow zygote,' YG is an impure yellow, and GG a 

 pure green, or 25%, pure yellow, 50% impure yellow, and 25'o Pure 

 green. 



(1) — The pure yeUow zygote (YY) formed by the union of two like 

 gametes is termed a "homozygote" and the impure yellow zygote 

 (YG) formed by the union of two unlike gametes a "heterozy- 

 gote." The.se two zygotes are "phenotypes," but genetically they 

 belong to different "genotypes." 



84 



