54 



INBREEDING AND OUTBREEDING 



obtained. Diagrammatically the expected production of 

 gametes and zygotes is as follows : 



gametes 



zygote 



Eggs 



Sperws 



gamete 



F a 2ygote 



FIG. 18. Diagram to illustrate Mendelism in a cross between long-spiked and short-spiked 



wheat. 



Let us express the whole matter mathematically. 

 The chance of an event happening in an infinite num- 

 ber of trials is expressed by a fraction of which the 

 numerator is the number of favorable ways and the de- 

 nominator the whole range of possibilities, both favor- 

 able and unfavorable, if each is equally likely to occur. 

 Hence, certainty is expressed in the figure 1. Further- 

 more, the chance that two or more independent events 

 will happen together is the product of their respective 

 chances of happening. The chance of an L egg meeting 



