498 



ZOOLOGY 



have been verified and enlarged, and his conclusions tested and 

 elaborated until we now include under "Mendelism" a large 

 body of exceedingly important facts and suggestive theories 

 and principles. 



Mendel hybridized varieties of garden peas. One true- 

 breeding variety is dwarf and another tall. When these are 

 artificially crossed, no matter which variety furnishes the pollen, 

 all the offspring are like the tall parent in height. The dwarf 



Pig. 253. 

 C Xc 



Parental Generation 



C(c) I St Filial Generation Fi 



(Self -crossed) 



CC 



CC 



CC 



Cic) 



C{c) 



CC. 



CC Cic) C{c) CC CC C{c) C{c) cc 



CC. 



Hybrids 



CC 



Hybrids 



CC 



.F, 



CC CC CC CC. 



Fig. 253. A general formula for Mendelian crosses. C represents any dominant quality; 

 c, the absence of the quality, or the recessive. The first £lial generation are all hybrids that look 

 like the dominant parent. If these are self-bred, the offspring of the second filial generation. Ft, 

 will be one-fourth pure dominant (,CC), one-fourth pure recessive (cc), and one-half hybrids (Cc) 

 which look and breed like their hybrid parents. CC and C(c) look alike, but breed differently. 

 Compare with Fig. 252. 



quality, which evidently must be represented in the offspring, 

 does not show in the body at all. He therefore concluded that 

 tallness was dominant over dwarfness. Dwarfness is said to be 

 recessive. 9, 



When these tall hybrids were self-fertilized, three-fourths of 

 their offspring were tall like the parents, and one-fourth were 

 dwarf like the dwarf grandparent. In the case of the dwarf 

 offspring the parents clearly transmit something which the 

 parent body does not possess. There were no intermediate 

 forms. Further breeding showed that these dwarfs were pure 

 dwarfs with no taint of tallness on them ; for when self -fertilized 

 they bred true dwarf, and continued indefinitely to do so. 



