THE INHERITANCE OF PRODUCTIVITY IN FARM LIVE STOCK.      287

                                          TABLE II

Relation of Number of Desirable Characters to Annual Production

That these particular desirable characters are inherited has now been
established and a reasonable idea of their mode of inheritance has been gained.

Early sexual maturity apparently depends on two independent dominant
genes, either of which can produce, for example, the onset of egg-laying in the
Rhode Island Red breed before the hens are 215 days old. One of these genes
is sex-linked, the other autosomal (Eo and E'E').

For high intensity of production, also, two dominant genes are necessary
(II and I'I'). Hens carrying gene 1 have alone an average winter-clutch size
greater than 2, but less than 2.6. Gene 1' gives a clutch size of about 2.6. Both
genes together increase the clutch size up to 3 or more eggs throughout the winter
season. Both genes are autosomal and cumulative in effect.

For winter pause there seems to be only one dominant gene, M. Desirable
birds therefore carry the recessive form, mm.

Broodiness has been found to be inherited on a two-factor basis. Two
dominant complementary genes, A and C, are necessary to produce it. There
is no evidence of sex-linkage and non-broody birds are of three general classes :
(1) those lacking both A and C ; (2) those carrying A and lacking C ; and (3) those
carrying C and lacking A. The latter two classes make it evident why broodiness
is so difficult to eliminate completely from a flock, since females of these con-
stitutions, though not exhibiting broodiness themselves, will produce broody
offspring if mated to males carrying the complementary gene they lack.

The data for persistency indicate that it is inherited on the basis of a single
dominant autosomal gene, P.

                                                                                                              L