INDEPENDENT MENDELIAN INHERITANCE 99 
down at one side and at the top of the checkerboard and any square is 
filled out by writing down the genetic formula of the gamete at the top 
of its column and the one at the end of its row. If the series are written 
in the order shown the diagonal 1-3 will pass through all homozygous 
combinations. The number of these is evidently equal to the number 
of possible combinations in the gametic series. The diagonal 2-4 
passes through all those combinations in which all three pairs of factors 
1 ABC ABc AbC Abe aBC aBe abC abe 2 
BC | ABc | AbC | Ale | aBC | aBc |} abC | alc 
ABC |ABC | ABC | ABC | ABC | ABC | ABC| ABC | ABC 
ABe | ABe Me ABc | ABe | ABe | ABc| ABe | ABe 
AbC | ALC | ALC AMC ADC | ALC AUC AbC | ALC 
Abe | Alc | Abe | Abc Des Abe Abe | Abe | Abc 
aBC | aBC | aBC | aBC | aBC | aBC | aBC | aBC | aBc 
aBec aBe aBe | aBc aBe | aBc 
VA 
abC | abC | abC | abC | abC | abc abC ai abC 
Soe ABc | AbC}| Abc | aBC | aBc | abC be 
abe | abe abe abe abe | abc abe | abe abe 
a 
4 =a 3 
Fic. 48.—Checkerboard method of analyzing expected results in F2 from a cross involving 
three pairs of allelomorphs. The ‘‘x”’ zygotes belong to phenotype ABC. Cf. p. 98. 
are heterozygous, and the number of these is also equal to the number of 
kinds of gametes. The bottom row gives the ratio which would be ob- 
tained by crossing the F’, back to the triple recessive form. The student 
will be able to determine other relations existing in checkerboards of this 
type. 
’ From a mathematical standpoint, students of genetics are interested 
in two things, the number and proportion of various types of individuals, 
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