6 MENDELISM 



The cross ( x ) is to be read as " fertilized by." This therefore 

 shows that a female germ-cell is fertilized by a male germ- 

 cell. A vertical line placed under the cross points to 

 the offspring which results from the fertilization, a simple 

 circle indicating the offspring without showing the sex. 

 Thus- x 



When the two germ-cells which unite in fertilization are 

 derived from two plants which are essentially similar, the 

 resulting offspring is said to be "pure-bred." When the 

 two parents show some well-marked difference, as in stature 

 or colour of flowers, the offspring is said to be " cross-bred," 

 so far as this particular character is concerned, and such a 

 cross-bred individual is called a " hybrid." 



The similarity or difference of the parents may be 

 represented by the sign, thus — 



£ and $ represent two similar parents ; 



$ and ?, or $ and ? represent two parents which differ in 



some important feature. 

 ? x $ 



represents the production of pure-bred 

 o offspring ; 



$ x^ $ x 



or 

 o o 



represents the production of cross-bred 

 or hybrid offspring. 



Now, when the parents show a marked difference, what 

 will the hybrid offspring be like ? Will it be like one of 

 the parents, and if so, which one ? Or will it be inter- 

 mediate between the two ? Clearly it cannot be like both. 



This is what Mendel studied experimentally. He 

 sought to discover the Law of Inheritance in these hybrid 

 offspring ; in other words, the law or laws governing the 

 resemblance between parent and offspring. 



