152 LOTSY AND KUIPER, A PRELIM, STATEMENT OF THE RESULTS OF MR. 
But still it so very desirable to continue these experiments, in 
order to solve this question. | 
As the present authors do not think there will be a good chance to 
continue them will the same material, now that Mr. HOUWINK’s experi- 
ment-station in Meppel has been dissolved, they decided upon the 
publication and discussion of the results hitherto obtained, although 
these are not complete, hoping some one else will take up the problem. 
Is it possible to explain these facts in the Mendelian way? 
In poultry as far as our experience goes, the hens are hetero- 
zygous X Y, the cocks homozygous Y Y for the sex-factor. If our 
facts have something to do with the sex chromosomes, there must bea 
difference between the two Y chromosomes. The first Y chromosome, 
let us call it Yr gives rose, comb, the second, YS single a 
Our Silky hen would be X Yr then, our Silky cock Yr Ys. 
this case, breeding true hens with single comb X Ys Ge be ee 
but these are never observed. 
It was also possible, that the X chromosome could cause the rose 
comb too; then the Silky hen should be Xr Yr, the cock Yr Ys; in 
this case the following combinations might exist: 
XTOY!) XE YEN ENEN EDS 
which should have a rose comb. 
But hens Xr Ys mated with cocks Yr Ys is Mg cocks with 
single comb, which do not exist. 
Sex-linked inheritance therefore can not explain the differences 
in the genetic constitution of our Silky cocks and hens. 
But the common mendelian inheritance (by means of an other 
chromosome) can also not give us an explanation. Suppose the 
Silky hen is called Ff in relation to sex, the cock ff, and the 
chromosome causing the rose comb R, that causing the single comb r. 
Then the Silky hens are RRFf the cocks Rrff. 
Now we get the following gametes. 
9 RF gow int. 
Rei rf. 
From the mating of these two can arise: 
RR Ff: a hen with rose comb. 
DEL FR Nee x y 
RRff. COR, = i 
Rr ff ” ” ” ” ” 

