78 HEREDITY AND SEX 



plant. If these meetings are random, the general or 

 average outcome will be : 1 pure yellow, 2 hybrid 

 yellows, and 1 pure green. 



It is now apparent why the pure yellows will always 

 breed true, why the yellow-greens will spUt again into 

 yellows and greens for 1:2:1), and why the pure 

 greens breed true. By this extremely simple assump- 

 tion the entire outcome finds a rational explanation. 



P\MESTS 



9 9 9 w 



Fig. 43. — " Checker " di:igram to show segregation and recombination of 

 factors. In upper hne, a black bearing gamete is supposed to unite with a 

 white bearing gamete to give the zygotes shown in Fi, each of which is 

 heterozygous for black-white here represented as allelomorphs, etc. 



The same scheme may be represented by means of 

 the above '' checker" diagram (Fig. 43). Black crossed 

 to white gives hybrid black, Fi, whose germ-cells are 

 black or white after segregation. The possible com- 

 bination of these on random meeting at the time of 

 fertilization is shown by the arrows in F^ and the results 

 are shown in the line marked Fo. There will be one 

 pure black, to two black-and-whites, to one pure white. 



