314 
the high producing line of milk pro- 
duction from 1.5 to 18.0 times as closely 
as they do the low line of milk produc- 
tion. If this paralleling of the high 
line production is averaged, it is found 
that the crossbreds resemble the high 
line of production 4.76 times as closely 
as they do the low line. These facts 
argue for the transmission of milk 
production by factors which show par- 
tial dominance. It would not seem 
that they argued for increased vigor 
of heterosis only because of the case 
of Crossbred No. 1, where the low line 
milk yield was definitely transmitted 
instead of the high yield. In fact it 
would appear that this crossbred is 
more likely to be a segregate of low 
milking factors from the high milking 
factors carried by her dam. 
Three levels of milk production are 
crossed in these experiments. The 
Aberdeen Angus cattle constitute the 
lowest level, the Jersey, Guernsey and 
Ayrshire cattle averaging about the 
same in milk yield constitute the in- 
termediate level of production and the 
Holstein-Friesian cattle having the 
highest yield represent the highest level 
of production. It is of some interest to 
compare the results of crossing the differ- 
ent levels. If we omit the result of Cross- 
bred No. 1 it is found that the Holstein- 
Friesian cows or bulls mated to the 
second group of cows or bulls (Jersey, 
Guernsey, or Ayrshire) produced three 
offspring who are 8.43 times as near the 
milk production of the high level on the 
average as they were the low line of 
production. 
The only cross involving the Hol- 
stein-Friesian and Aberdeen Angus, 
Crossbred No. 44, was 2.2 times as 
close to the high line of production as 
she was close to the low line of her 
parent’s milk yield. 
It is of interest to note in this con- 
nection that Crossbred No. 44’s milk 
yield resembles closely the milk yield 
of the intermediate group (Jersey, 
Guernsey and Ayrshire) of these exper- 
iments. 
5’ Wilson, James. 1911, The Inheritance 
Dublin Soc. Vol. 13, pp. 89-112. 
The Journal of Heredity 
The crosses involving the second 
level of milk production (Jersey, Guern- 
sey and Ayrshire) mated to the third 
group Aberdeen Angus, had crossbred 
offspring resembling the high line 7.7 
times as closely as they did the low 
line of production. This figure com- 
pares favorably with that of the Hol- 
stein-Friesian x Jersey crosses. 
If the crosses are compared to de- 
termine what effect the high line on the 
sire’s side of the cross may have in com- 
parison with the effect produced by the 
high line being on the dam’s side of the 
cross it is found that the results in the 
three lines are contradictory. When 
the Holstein-Friesian sires were mated 
to second class dams, Guernseys, the 
offspring resembled the high line 11.3 
times as closely as she did the low line. 
When the Jersey sire, second class, was 
mated to the Holstein-Friesian cows, 
highest class, the milk production once 
resembled the high class 2.7 to 1, and 
once the low line 7.7 to 1. The crosses 
involving the highest milk line, Hol- 
stein-Friesian bull, to the lowest milk- 
ing line Aberdeen Angus cow produced 
an offspring resembling the high line 
2.2 times as closely as the low line. 
The crosses of the second level in milk 
production to the third level show that 
when the higher level is on the sire’s 
side the daughters resembled the high 
line 3.6 times as closely as they do the 
low line. When the higher level is on 
the dam's side the daughters resembled 
the high line 9.34 times as closely as 
they did the low line. It seems doubt- 
ful from these results if there are modi- 
fying sex linked factors present. 
MENDELIAN TRANSMISSION OF MILK 
YIELD 
The literature on this subject is 
surprisingly meag r considering the 
economic importance of milk and its 
products. Of those studies which are 
available that made by Wilson® is one 
of the earliest. This paper is devoted 
to showing that with such a breed as 
the red Dannish there may be wide 
of Milk Yield in Cattle. In Sci. Proc. Roy. 
