Inheritance of Characteristics in Domestic Fowl

CHAPTER IX. COMB-LOP .

In races having a large single comb this is usually erect in the male, but in the female lops over to the right or left side of the head. This lop is determined before hatching; indeed, in the male it may be ascertainable only in the embryo or in the recently hatched chick. The position of the comb is permanent throughout the life of the pullet and hen and, if pressed to the opposite side, it quickly returns to its original position. At one time I entertained the hypothesis that its position was determined by the pressure of the foot against the head while the chick was still within the shell; but after finding the comb lying both to the right and to the left when in contact with the foot I abandoned this hypothesis as untenable. It seemed possible that this position is hereditary, and so data were collected to test this hypothesis. It is not always easy to decide definitely, even for the female, as to the direction of the lop; for the anterior part of the comb may lop to the right, the posterior part to the left, or vice versa. In that case one selects the larger or better defined lopping portion to designate as the lop. This is usually the posterior portion of the comb. However, such doubtful cases may be omitted from consideration here, as there are plenty of examples of well-defined lop on both sides of the head.

Table 56.

Both parents with right lop.
Pen No.	No. of mother.	No. of father.	Offspring.
Pen No.	No. of mother.	No. of father.	Right.	Left.
817	6188	3900	7	8
817	6406	3900	12	17
831	1011	4213	7	16
831	3040	4213	13	10
831	4219	4213	4	21
831	6602	4213	6	15
833	1310	4222	4	7
833	4361	4222	6	4
833	7519	4222	2	4
904	4714	7870	6	7
			67	109
Both parents with left lop.
841	3867	3890	3	9
841	4663	3890	9	7
903	9824	8463	6	5
			18	21
Mother left lop, father right.
831	1980	4213	9	17
904	3901	7840	4	3
904	7645	7840	6	3
			19	23
Mother left lop, father right.
903	3946	8463	2	0
903	4079	8463	7	2
903	4082	8463	11	6
			20	8
Summary.
Parents		Offspring.
Parents		Total.	Right.	Left.
			P. ct.	P. ct.
Both with right lop		176	38	62
Both with left lop		39	46	54
Mother left lop, father right		42	45	55
Mother right lop, father left		28	71	29

From table 56 it appears, summing all cases, that there are more left-lopping offspring than right-lopping as 161 to 124 or as 56.5 per cent to 43.5 per cent and that this excess holds whether both parents are right-lopping, or both left-lopping, or the mother left and the father right. Only in the case when the mother is right-lopping is there a majority of offspring of the same sort, but here the numbers are too inconsiderable to carry much weight. Although there is not clear evidence of any sort of inheritance, it is probable that the position of the lop is not determined by a single factor, but by a complex of factors.

The conclusion that right and left conditions are not simple, alternative qualities accords with the results obtained by others. Thus Larrabee (1906) finds that the dimorphism of the optic chiasma of fishes (in some cases the right optic nerve being dorsal and in others the left) is not at all inherited, but in each generation the result is strictly due to chance. This is, perhaps, the same as my conclusion that the hereditary factors are complex. Lutz (1908) finds that in the mode of clasping the hands interdigitally the right thumb is uppermost in 73 per cent of the offspring when both parents clasp with right thumb uppermost, but in only 42 per cent of the offspring when both parents clasp with left thumb uppermost. The mode of clasping is inherited, but not in simple Mendelian fashion.