MENDEL'S LAW OF HEREDITY 



31 



breeder may not know whether the characteristics found in this 

 strain are permanent or not. If the type be pure the characteris- 

 tics will be perpetuated in future generations; but if it is a mixed 

 type the succeeding generations will be variable. It is always 

 necessary for him to establish the purity by actual trial through 

 one or more generations. 



Mendel's Law of Heredity. When the minute growth of 

 pollen unites with the ovule in the pistil a union is formed which 

 develops into a new individual. This seed will produce a plant 

 with certain characteristics. If the pollen is from a yellow variety 

 of corn and the pistil is on a white variety, the seed produced will 

 be either yellow or white, not both colors. The corn grown from 

 this seed, if no other crossing be allowed, will be one-fourth pure 

 white, one-fourth pure yellow, and two-fourths (one-half) will 

 appear as yellow but will produce both white and yellow offspring 

 in the next generation. The proportion in the first generation is 

 MY+MYW+MW (if Y = yellow and W = white). 



In the following generations the one-fourth pure yellow will 

 produce yellow without mixture; the pure white will produce pure 

 white without mixture, but the mixed (or hybrid) two-fourths 

 will produce either yellow or white corn in the same proportions 

 as before, breaking up in each generation, thus: 



First 

 Generation 



Y(hybrid) 



Second 

 Generation 



1/4 Y (pure) 



2/4 Y (hybrid) 



1/4 W (pure) 



Third Fourth Fifth 



Generation Generation Generation 



Y (pure) Y (pure) Y (pure) 



(1/4 Y (pure) Y (pure) Y (pure) 



[1/4 Y (pure) Y (pure) 



(1/4 Y (pure) 

 2/4 Y (hybrid) \2/4 Y (hybrid) 2/4 Y (hybrid) 



1 1/4 W (pure) 



[1/4 W (pure) W (pure) 



1/4 W (pure) W (pure) W (pure) 



W (pure) W (pure) W (pure) 



The net results, expressed in fractions of the first hybrids, 

 would be in the three generations: 



3/8 Y (pure) + 2/8 Y (hybrids) + 3/8 W (pure). 



The law which covers these results, when individuals with 

 such different characters are crossed, was first discovered by the 

 Abbot of Bunn, named G. J. Mendel, who published his result 

 prior to 1865. Similar results have been attained by other experi- 

 menters in recent years. Mendel experimented with garden peas 

 and contrasted them in such characters as color of blossom 



