SEGREGATION AND DOMINANCE 



189 



When a homozygous individual with dark curly 

 hair crosses with a homozygous individual with light 

 straight hair, all the offspring have dark curly hair. 



The dark curly-haired individuals of this second 

 generation, however, are heterozygous with respect 

 to each of these two hair characters. When any two 

 individuals having this particular genotypic compo- 

 sition mate, therefore, 



they may produce any N * [GENOTYPE PHENOTYPE 

 one of four possible 

 phenotypes dark 



curly, dark straight, I ^ I ^ |/k/*/://r/y 

 light curly or light 

 straight haired individ- 

 uals. These four phe- 

 notypes in turn will 

 present nine different 

 genotypic combina- 

 tions out of sixteen pos- 

 sible cases, as shown in 

 Figure 46. 



Figure 45 further- / $) \Lgfit stni^t I J 

 more serves to. make I le \ \ \ J6 , 



dear, first, the distinc- FIG. 46. Diagrams showing the pos- 



tion between somato- 



plasm and germplasm ; 



second, the maturation 



of germ-cells ; third, the 



segregation of gametes ; and fourth, the formation of 



zygotes in sexual reproduction. 



The cells of the somatoplasm are represented as 



Dark strviQht 



Light curly 



sible genotypic and phenotypic com- 

 binations resulting when two hetero- 

 zygous individuals, with dark curly 

 hair, mate. Symbols are the same 

 as in Figure 45. 



