536 HEREDITY 



inherited genes for large size and high yield, but, due to unfavor- 

 able surroundings, it is small and yields poorly. The amount of 

 protein in the kernels of Wheat depends very much upon the cli- 

 mate. Most plants inherit the ability to develop chlorophyll, 

 the pigment giving them a green color, but if grown in the dark 

 no chlorophyll develops and the plants are yellow or white instead 

 of green. Livestock, however well bred, do not show their 

 qualities in full unless properly fed and sheltered. It is obvious 

 that upon external appearances one can not accurately judge 

 what plants and ainmals have inherited or what they will trans- 

 mit, for they have latent genes and also their visible characters 

 have been more or less modified by environment. We are 

 advised to pick our seed corn in the field, so that we may take 

 into account the surroundings of the plants and thereby judge 

 more accurately the constitution of the plants from which seed 

 is selected. Only through breeding experiments can we accu- 

 rately determine the genes of plants or animals. Two plants or 

 animals may be very similar in appearance but be very different 

 in genes contained. Individuals alike in genes contained are of 

 the same genotype, while individuals similar in appearance but 

 not in genes contained constitute a phenotype. 



Laws of Heredity 



Heredity is so apparent ia both plants and animals that it has 

 attracted the attention of men in all ages. Man's dealings with 

 his fellowmen and with the plants and animals upon which he 

 has depended for food has forced him to reckon with heredity 

 throughout the history of mankind. However, to observe 

 heredity in operation is one thing, and to learn the laws of its 

 operation is a very different thing. It is plain to all of us that 

 the characters of the parents tend to reappear in the offspring, 

 but concerning the laws governing their appearance there is stiU 

 much to be learned. Why do some parental characters appear 

 in the offspring while others do not? Why do the individuals 

 of an offspring differ in the parental characters they display? 

 Why do offspring often have characters that neither of their 

 parents have? For such questions as these students of heredity 

 are still trying to discover satisfactory answers. 



Value of knowing the laws of Heredity. — The history of sci- 

 ence teaches us that man's ability to control nature's forces 



