624 IMPROVEMENT OF LIVING THINGS BY MAN 



parents 



3:1 ratio 



Practical Exercise 9. Make a colored diagram for your workbook to show 

 the following examples of Mendel's laws of dominance and segregation. 

 Work out your diagram to the F 3 generation: Colored flowers of peas are 

 dominant over white. Green color in pod is dominant over yellow. Gray 

 coat color in mice is dominant over white. 



The practical results. Already some progress has been made 

 in the application of Mendel's laws to hybridization. The United 



States Depart- 

 ment of Agricul- 

 ture is now 

 producing cold- 

 resistant fruits 

 and grains in the 

 Alaska experi- 

 ment station. A 

 hybrid which is a 

 cross between the 

 watermelon and 

 the citron has 

 produced a fruit 

 that will resist 



acter, and the white color is a recessive character. If two rats ' 



of the second generation (Fi) are mated, why would they probably fungUS disease of 



have one white and three black offspring ? , .„ 



melons. Kust- 

 resisting wheats also have been produced in this country; while 

 in England experiments on wheat have resulted in the production 

 of resistance to disease, " hardness " of grain, and increase in the 

 size of the grain and of the head — all characters which mean 

 greater productiveness. But most of the hybridizing is still done 

 on a hit-or-miss principle, with few permanent results. Luther 

 Burbank, the great hybridizer of California, destroyed tens of 

 thousands of plants in order to get one or two with the charac- 

 ters which he wished to preserve. 



Animal breeding. It has been pointed out that the domesti- 

 cation of wild animals — horses, cattle, sheep, goats, and dogs — 

 marked great advances in civilization in the history of mankind. 

 As the young of these animals were bred in captivity, the people 

 owning them would undoubtedly pick out the strongest and best 



In rats, the black color has been found to be a dominant char- 



