

SEGREGATION AND DOMINANCE 143 



extensive scale. In Figure 47 dominant characters 

 are represented by capital letters, while recessives or 

 absences are indicated by corresponding small letters. 



When a smooth, or non-rosetted (r), short-haired 

 (S), pigmented (P) guinea-pig is crossed with a 

 rosetted (R), long-haired (s), albino (p) guinea-pig, 

 all the offspring appear to be of one phenotypic 

 constitution, namely, rosetted, short-haired, and 

 pigmented (RSP). Their genotypic constitution is 

 represented by the formula RrSsPp. These six 

 factors may form eight possible triple gametes, as 

 follows : RSP, RsP, RSp, Rsp, rSP, rsP, rsp. When 

 two germ-cells each made up of these eight triple 

 gametes unite in sexual reproduction, they will give 

 rise to sixty-four (8 X 8) possible zygotes as dis- 

 played in Figure 47. 



An analysis of Figure 47 shows among the off- 

 spring eight different phenotypes in the ratio of 

 27:9:9:9:3:3:3:1 and 27 different genotypes in 

 the proportions indicated on the opposite page. The 

 order of the three pairs of symbols is changed from 

 that in Figure 47 to emphasize the fact that with 

 independent unit characters the order is immaterial. 



12. CONCLUSION 



Although the ratios for more than a trihybrid 

 were computed by Mendel, the experimental test 

 has never been carried out, since it involves such 

 large and complicated proportions. 



In the case of four differing unit characters in the 

 parental generation, the offspring of the quadruple 





