ZOOLOGY 



Develop- 

 ment of a 

 pure-bred 

 strain 



rayed (no-red); so "red" X "no-red" would give 

 "red," and "no-red" X "no-red" would give orange 

 rays. If we use R for "red" and r for "no-red," the 

 formula is as follows : 



Rr X rr = Rr and rr (half of each) 



Of course the actual crosses are between the gametes, 

 and are to be expressed thus : 



R X r = Rr 



r X r = rr 



8. Having now obtained a number of plants like the 

 original one, these could be crossed together, and would 

 give homologous or pure-bred reds. 



Thus Rr X Rr will give RR, Rr, rR, rr, a quarter of 

 each being the theoretical expectation. The gametes, 

 being R and r (in equal numbers) on each side, and com- 

 bining at random, give this result as follows : 



R 



The lines indicate the possible combinations, each one 



as likely to happen as any other. The homozygous 



reds, if isolated, will now come true, except so far as 



they may be influenced by pattern and dilution factors, 



and environmental conditions, as explained below. 



Production 9- There had been known in cultivation since 1889 



of wine-red a variety of the garden sunflower called "primrose," 



sunflower. ... r 



The 9) 3, 3, having the rays pale yellow, the color of the English 

 primrose. This had arisen as a "sport" from the or- 

 dinary kind, and the same variation has since been ob- 

 served in the prairie sunflower. Knowing that the red 

 of the red sunflower was chestnut only because on an 



i ratio 



