424 GENETICS IN RELATION TO AGRICULTURE 
which can be used to describe any pedigree. The scheme described 
below is essentially Pearl’s system with some minor changes. In the dia- 
gram (p. 423) solid lines with circles containing numbers indicate matings 
between the individuals represented by the letters which they connect. 
Dotted lines lead from the matings to the individuals produced. The 
order of precedence in nomenclature may be varied to harmonize with 
the former practice of the investigator. Table LVI indicates every pos- 
sible combination of Ff, individuals to produce F3. By priming the 
mating numbers reciprocal back crosses can be indicated and the kinds 
of individuals produced may be similarly distinguished. For example, 
following the order of precedence suggested below the diagram, Z X Y 
is mating 8 and produces # but Y  Z is mating 8’ and produces E’ 
while H or H’ & X is mating 26 and produces, let us say, N and X X E or 
E’ is mating 26’ and produces N’. The order of mating in intra-fraternal 
crosses will be immaterial except in the case of sex-limited characters 
when individuals may be distinguished by subscripts. Pearl explains 
the arrangements of mating numbers in the table as follows: 
A word should be added in regard to the system by which the numbers 
have been assigned to the matings. It might at first sight appear as 
though the arrangement were an entirely haphazard one. It is not. 
On the contrary the numbers will be found to conform to the following 
general principles, which seem likely to be of aid in practical work, as 
tending to make it easy to recall from a number just what its particular 
pedigree looks like. 
1. All even numbers refer to back-cross matings. 
2. All odd numbers refer to co-fraternal or intra-generation matings 
(not back-crosses). 
3. Matings below 2 are of parental generation individuals; between 2 
and 8 inclusive are of F’; individuals; matings over 10 are of Ff. individuals. 
4, Even numbers from 10 to 36 inclusive designate back-crosses of 
F, individuals with their grandparents, or individuals of the grand- 
parental generation. 
5. Even numbers from 40 up designate back-crosses of Fy individuals 
on F, individuals. 
6. In the case of the odd numbers from 11 up it is, 7n a general way, 
true that the smaller the designating number of a mating the more closely 
related to each other are the two individuals entering that mating likely 
to be. This principle of assigning the numbers could not be so precisely 
followed as the preceding five, but still is perhaps worth a little. 
In using such a system it 1s of course necessary to have the basic 
table always at hand. The diagram is quickly drawn and the typewritten 
tables may be pasted in note books or both diagram and table may be 
printed on cardboard for use in breeding pens or plots. 
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