398 



THE NEW INDIVIDUAL 



Part IV 



r?-^ RIGHT ABM OF 



^<,y^ \ ; \ CHAOMOSOME nL 



^ X CHROMOSOME 



CHROMOCENTER <<^ 







CHROMOSOMES FROM OVARIAN TISSUE 



(Same enlarqement) 



LEFT ARM OF 

 CHROMOSOME 



Fig. 20.8. A, chromosomes in the saUvary glands of a fruit fly. Although they 

 belong to minute flies these chromosomes are among the largest that have been 

 observed. (From Altenburg: Genetics. Copyrighted by Henry Holt and Co. Re- 

 printed with their permission.) 



Experiments Illustrating Mendelian Principles 



Monohybrid Cross. A monohybrid cross may be illustrated by cross breed- 

 ing one parent having a long line of black ancestors (pure-line), and another 

 parent having a long line of white ones. The offspring produced by animals 

 differing in one character, such as color, are monohybrids. 



A pure-line black guinea pig is bred to a pure-line white. The male may 

 be black and female white or vice versa (Fig. 20.9). In a pair of genes, e.g., 

 the gene for white, the recessive, is expressed by w in small type; the gene 

 for black, the dominant, by W in capitals. The formulas for the parents (P) 



