1150 
Journal of Agricultural Research 
Vol. V, No. 25 
ADVANTAGES OF LITTER SIZE INHERITANCE STUDIES 
Accepting the figures for litter size as reasonably representative of 
the hereditary constitution, there are a number of reasons that make 
them desirable material for inheritance studies. The most important of 
these is the fact that the male mated to a female probably does not affect 
the number at a birth. Instead the size of litters a sow produces repre¬ 
sents the segregation of the tendencies transmitted to her by her father 
and mother. Suppose a sow produces a litter of four pigs and is herself 
from a litter of seven, the seven does not determine in any way the four, 
but instead the segregation of some tendency transmitted by her sire or 
dam is represented. The only check available on this tendency in her 
sire is the size of litter in which he was farrowed, while the same holds for 
the dam, except that her own breeding performance may give an addi¬ 
tional idea. 
METHOD OF RECORDING THE DATA 
The data on the animals studied were recorded as follows, the figures 
representing the size of litters in which the individuals were farrowed: 
Animal 
4 
Dam 
7 
Grandsire 
4 
Grandam 
9 
The size of litters produced by sows whose sires came from litters 
of four and whose dams came from litters of seven should give an idea 
(through the variations recorded) of the hereditary factors involved. 
It is admissible that all grandams or all grandsires farrowed in the same 
size of litters may be different in hereditary make-up, but there should 
be enough individuals alike to make the frequency curves at least sug¬ 
gestive. For convenience, the grandparental generation will be let¬ 
tered “P,” the parental generation “F t ,” and the filial generation “F 2 ,” 
although it is clearly to be understood that this notation does not have 
the regular Mendelian significance. 
DEVIATIONS PER GENERATION 
The mean size of 1,770 litters in the P generation was 7.84±0.3494. 
The standard deviation was 2.18±0.2461. This gives a coefficient of 
variability of 27.80 for this generation. 
The mean size of 885 litters for the ^ generation was 7.82 ±0.4897. 
The corresponding standard deviation was 2.16±0.3462. The coeffi¬ 
cient of variability here involved was 27.60, practically the same as that 
of the grandparental generation. 
The mean size of 885 litters in the F 2 generation was 7.91 ±0.4965, 
while the deviation was 2.i9±o.35ii, giving a coefficient of variability 
of 27.55. (See Table I.) 
