GENETICS: PEARL AND PATTERSON 
59 
in the ancestral series be plotted to the generation number as a base, 
the points so obtained will form a curve which may be designated as the 
curve of inbreeding. 
It will be noted that the coefficient of inbreeding Z is the percentage 
of the difference between the maximum possible number of ancestors 
in a given generation and the actual number realized. The coefficient 
may have any value between 0 and 100. When there is no breeding 
of relatives whatever (that is, in the entire absence of inbreeding) its 
value for each generation is 0. As the intensity of the inbreeding in- 
creases the value of the coefficient rises. 
S/ 
/ / 
4< / 
n 
11 I 
/ / 
// / 
// / 
/ /■ 
f-r 
/ / 
// 
/ / 
// ^ 
1 
40 
CENELRA T/O/VS 
FIG. 1. —DIAGRAM SHOWING THE INBREEDING CURVES FOR A RANDOM SAMPLE OF 
THE GENERAL POPULATION OF AMERICAN JERSEY COWS. THE TWO HEAVY LINES GIVE 
THE UPPER AND LOWER LIMITING VALUES FOR THE SUCCESSIVE MEAN INBREEDING 
COEFFICIENTS. THE TRUE VALUE OF THE CURVE LIES SOMEWHERE IN THE RULED 
AREA BETWEEN THESE HEAVY LINES. FOR COMPARISON THE CURVES FOR CONTINUED 
BROTHER X SISTER (B X S), PARENT X OFFSPRING (P X O). AND FIRST COUSIN X FIRST 
COUSIN BREEDING ARE INCLUDED. Ci X Ci DENOTES SINGLE COUSIN MATINGS, AND 
C2 X C2 DOUBLE COUSIN MATINGS. 
It is obvious that this method provides for the first time a means of 
examining statistically the degree of inbreeding which exists on the 
average in a population, or in any differentiated group of a population. 
It is the purpose of the present note to give in a very brief and prelimin- 
ary way certain of the results of such a statistical examination of in- 
breeding in American Jersey cattle. 
The first step in the treatment of the problem consisted in working 
out complete pedigrees to and including the eighth ancestral generation 
of 254 individual animals registered in the Herd Book of the American 
