The genetic and the operative evidence relating to secondary sexual charactersMorgan, Thomas Hunt
Science
The genetic and the operative evidence relating to secondary sexual characters
Morgan, Thomas Hunt
Genetics; Poultry; Sex (Biology)
Of the 7 cock-feathered males, one was like the F₁ _castrated_ males;
another had a similar back, but a darker and differently marked breast;
2 were game-cock type; 3 were odd birds much like the game cock above
except for absence of black, with reddish heads without any black. The
males may be approximately classified as follows:
+----------+-----------------------------------------------+
| | Back-cross F₁ ♀ by game ♂. |
| +---------------+--------------+----------------+
| | Hen-feathered | Intermediate | Cock-feathered |
| | ♂. | ♂. | ♂. |
+----------+---------------+--------------+----------------+
| F (or K) | | 1 | 1 |
| (C) | | 1 | 2 |
| B | | | 2 |
| A | | | 2 |
| | | +----------------+
| | | | 7 |
+----------+---------------+--------------+----------------+
Four or five types may then be recognized in this rough grouping. None
of the groups seem uniform and probably might be split again.
D. THE NUMBER OF COLOR FACTORS INVOLVED.
The theoretical expectation for two pairs of factors calls for 4 classes
in the back-cross, but this assumes that the parent type used for
back-crossing contains all (here 2) recessives. But this simple
assumption can not be true in this case, for the F₁ bird would have been
like the Sebright. On the 3-factor assumption the expectation for the
back-cross is 8 classes, but this would apply only if the game were the
triple-recessive form, which, again, it is not, as shown by the F₁
cross. But if the dominance of one or more of the Sebright color factors
is incomplete, then either a 2 or 3 factor assumption might apply to the
back-cross.
If only 2 pairs of factors are present we should expect to recover the
game type once in 16 cases in F₂. But, as will be shown, only 1 game was
recovered out of the 49 F₂ females. This result fits better with a
3-factor assumption, for even with the small number in the back-cross
the indications are that more than 4 classes are present.
In the F₂ birds at least 11 classes may be distinguished, and some of
these appear composite. For 3 factors the maximum number of possible
classes (including heterozygotes) is 27. We can recognize at least 11 F₂
classes amongst the females alone, and a few others are doubtfully
present in the males.
In favor of the view that the heterozygous classes are here different
from the homozygous, the following evidence may be utilized:
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account