2o6 BREEDING 



Our next duty is to predict the result of mating 

 these hybrids from a knowledge of the contents of 

 their germ cells. The first step towards this end is 

 to determine the number of possible combinations of 

 any two of the characters, yellow, green, round 

 and wrinkled, except such combinations as involve 

 the association in one gamete of the two characters 

 of a pair ; that is to say, except YG and EW. Also 

 there cannot, of course, be gametes with the formula 

 YY, GGr, EH, or WW : it is only zygotes, which are 

 of double structure, that can contain two of the same 

 factor. With these exceptions the number of possible 

 combinations of the characters Y, G, E and W are 

 YE, YW, GE, GW. AU that we have to do, there- 

 fore, to predict the result of mating the yellow-round 

 hybrids together is to determine the number and 

 relative frequency of the possible combinations of 

 these four types of gametes. And this is mostly simply 

 done by means of a sixteen-square Table. The for- 

 mulae for the four types of ^ gamete are written along 

 the top, and four similar formulae for the $ gametes 

 on the left side of the Table on the opposite page. 



Here, again, four horizontal squares are referred 

 to as a row, and four squares superimposed vertically, 

 as a column. 



Let us now see what the various kinds of zygotes 

 formed by the union of the four kinds of gametes 

 are, and write the formulae for each in the square 

 formed by the intersection of the column relating 

 to the male gamete concerned, the formula of which 

 is written at its top, with the row relating to the 



