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Bulletin - Massachusetts Agricultural Experiment Station (Volume no.379-398) online

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weeks of age. Since there is a sex-dimorphism, the sexes were considered sep-
arately. The chicks were classified as either rapid or slow feathering at 12 days



6 MASS. EXPERIMENT STATION BULLETIN 396

and the same chicks were again classified as + or — for back feathering at 8
weeks. The particular point of interest in these data is the percentage of +
and — birds in the si and SI groups, respectively. Table 4 presents the data.

Table 4. — Relation of Chick Feathering at 12 Days to Back
Feathering at 8 Weeks. 1938 and 1939.

Chick Back Males Females

Feathering Feathering



at 12 Days at 8 Weeks Number Percent Number Percent

Control Line

+ 21 95.4 108 74.5
si,

1 4.6 37 25.5

+ 274 23.9 117 12.3
SI,

873 76.1 838 87.7

Line 1, Bred for Complete Back Feathering at 8 Weeks

+ 39 97.5 70 78.6
si.

1 2.5 19 21.4

+ 117 49.2 58 34.3
SI.

121 50.8 111 65.7

Line 2, Bred for Absence of Back Feathering at 8 Weeks

f + 0.0 0.0

si i

[- 0.0 1 100.0

+ 6 8.3 1 1.8
SI.

66 91.7 55 98.2



Almost 24 percent of the males in the control line that had not exhibited rapid
feathering at 12 days of age showed back feathering at 8 weeks of age. In line 1
about half of the males that were classified as slow feathering when 12 days old
developed back feathering when 8 weeks old. Only 8 percent of the males in
line 2 showed back feathering when 8 weeks old. These facts suggest that the
presence of the recessive gene si in heterozygous condition causes the develop-
ment of some back feathering in males at 8 weeks. The fact that almost all of
the male chicks that had shown themselves to be homoz^'gous for gene si at 12
days later developed some back feathering, points to the sex-linked gene si as of
major importance in the development of back feathering at 8 weeks.

About 75 percent of the females showing rapid feathering at 12 days had
complete back feathering at 8 weeks of age. As has been previously pointed out,
every female will show some feathering on the back at 8 weeks, making a classi-
fication for back feathering difficult and of questionable reliability. For this
reason, more stress has been laid on the male side of the population. Since
females can carry gene si in simplex state only, its influence on back feathering
may be less in this sex. In all lines, females that lacked gene si were much less
likely than males of the same line to develop back feathering at 8 weeks.

These earlier data point to the importance of the sex-linked gene si in its re-
lation to feathering in the back region. Careful attention is given later to its
relation to degree of feathering and to other inheritance phases of the problem.



RAPID FEATHERING IN RHODE ISLAND REDS 7

Relation Between Feathering at Twelve Days and Degrees of Back
Feathering at Eight Weeks

In the last two generations, hatched in 1941 and 1942, the chicks were all
classified for the sex-linked gene at 12 days of age. At 8 weeks of age all chicks
were again classified for back feathering into grades to 4. Since there were so
few chicks in grade 4, which implies complete feather growth on the back without
any pin feathers, this grade is scarcely worth considering in these studies. Males
particularly are known to vary widely in the degree of feathering over the back.
The data in table 5 show how the presence or absence of the sex-linked gene si
for rapid feathering affects the degree of back feathering in Rhode Island Reds
in the three lines.

There appears to be an important relationship between the recessive sex-
linked gene si for rapid feathering and the degree of feathering over the back at
8 weeks. In the control line males, slightly over 10 percent that carried gene si
in homozygous condition had no back feathering at 8 weeks of age. This fact
indicates that such males must have lacked the necessary autosomal genes to
produce rapid back feathering. In line 1, slsl males all had some back feather-
ing at 8 weeks. In line 2, the sex-linked gene was not present in the males.

Since sex-linked gene si shows its effect in females in the hemizygous or single
dose stage, a greater percentage of the females than males in all three lines was
observed to have tail growth at 12 days of age. Only one si female produced in
two generations, failed to develop some back feathering at 8 weeks. All other
females that had tails at 12 days fell into grades 2, 3, or 4 when 8 weeks old.
One very significant fact should be noted in this connection; in the control line
58 percent of si females were graded 3 or 4 at 8 weeks, while in line 1 , 96 percent
were given these two grades. In other words, the si females in line 1 after seven
years of selection for early back feathering must have approached a homozygous
condition for autosomal genes concerned.

Males lacking tails at 12 days may be of two genotypes, Slsl or SlSl, as far as
the sex-linked gene is concerned. Table 5 shows that about 22 percent of such
males lacked back feathering completely at 8 weeks in the control line and that
most of the others fell in grades 1 and 2. In line 1 there were no SI males com-
pletely lacking in back feathering and about 97 percent fell in grades 2 and 3.
The SI males of line 2 were mostly in the grade for back feathering, with about
7 percent in grade 1. In line 1, selection on the basis of back feathering had been
effective in the absence of the sex-linked gene. It is very probable also that the
SI males in line 1 were all heterozygous for gene si. In the control line fewer
males were heterozygous for gene si and probably none were heterozygous for
this gene in line 2.

Females that failed to develop tails at 12 days must have completely lacked the
recessive sex-linked gene si. In this group, any differences in rate of back feather-
ing between the three lines must have been due to the effects of selection on auto-
somal genes. The SI females in the control line fell mostly into grades 2 and 3
for back feathering at 8 weeks; the SI females of line 1 fell only in grades 2 and 3;
and the SI females of line 2 were mostly in grades 1 and 2. Females of line 1
were definitely superior to the controls and those of line 2 were decidedly inferior
to the controls.

Breeding Results Concerned with the Sex-Linked Gene and Other
Possible Genes Affecting Back Feathering

Table 6 shows the character of the progeny produced in ten generations from
eighteen different types of matings. Progeny where grouped into either -(- or —
classes with respect to back feathering at 8 weeks of age.



MASS. EXPERIMENT STATION BULLETIN 396



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Online LibraryMassachusetts Agricultural Experiment StationBulletin - Massachusetts Agricultural Experiment Station (Volume no.379-398) → online text (page 64 of 77)