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 split again into 

 yellows and greens (or 1:2:1), and why the pure 

 greens breed true. By this extremely simple assump- 

 tion the entire outcome finds a rational explanation. 



o 



F. 1 



t 







FIG. 43. " Checker " diagram to show segregation and recombination of 

 factors. In upper line, 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, F\, 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 FI and the results 

 are shown in the line marked F 2 . There will be one 

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



