56 ZOOLOGY 



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 



Develop- 

 ment of a 

 pure-bred 

 strain 



Production 

 of wine-red 

 sunflower. 

 The 9, 3, 3, 

 i ratio 



8. Having now obtained a number of plants like the 

 original one, these could be crossed together, and would 

 give homozygous 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. K 



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. 



9. There had been known in cultivation since 1889 

 a variety of the garden sunflower called "primrose," 

 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 



