In the case of my recessive pile, my interpretation is that when the
chromosomes corresponding to two distinct characters such as colour and
absence of colour are formed they do not separate from each other
completely. Whether the mixture of the chromosomes occurs in every resting
stage of the nucleus in the successive generations of the gametocytes, or
whether it occurs only in the synapsis stage preceding reduction division,
it is not surprising that the colloid substance of the chromosomes should
form a more or less complete intermixture, and that the two original
chromosomes should not be again separated in the pure condition in which
they came into contact. A part, greater or less, of each may be left mixed
with the other. This is the probable explanation of the fact that the
recessive white plumage has some of the pigment from the dominant form.
Segregation, the repulsion between chromosomes, or chromatin, from gametes
of different races may occur in different degrees from complete
segregation to complete mixture. When the latter occurs there would be
no segregation and the heterozygote would breed true. The most interesting
fact is that a given factor in the cases I have described, namely, colour
of plumage and pigmentation, of skin in the Jungle fowl and the Silky, is
not a permanent and indivisible unit, but is capable of subdivision in any
proportion. Bateson has already (in his Address to the Australian meeting
of the British Association) expressed the same conclusion. He states that
although some Mendelians have spoken of genetic factors as permanent and
indestructible, he is satisfied that they may occasionally undergo a
quantitative disintegration, the results of which he calls subtraction or
reduction stages. For example, the Picotee Sweet Pea with its purple edges
can be nothing but a condition produced by the factor which ordinarily
makes the fully purple flower, quantitatively diminished. He remarks also
that these fractional degradations are, it may be inferred, the
consequences of irregularities in segregation.