So it's like two copies of the modifier cancel out one copy of the frizzle gene.
Show quality birds only carry one frizzle gene (F) and are heterozygous F/f. They also carry two recessive genes for
no modification of the frizzle gene mf/mf. The genotype of a frizzled show quality bird is F/f mf/mf (Hutt,1949)
Hutt,F.B., 1949. Genetics of the Fowl. pp.107-109 McGraw Hill Book Company
My analysis of a few papers on the subject enjoy the read.
When thinking about modifiers, it must be kept in mind that modifiers can be dominant or heterozygous incompletely dominant or even recessive. Modifying alleles that are homozygous dominant may alter a phenotype differently than if the modifying alleles were heterozygous. The
incompletely dominant frizzling phenotype and the action of its
recessive modifier is a good example of how modifiers can work to produce differing phenotypes; there are 4 different phenotypes that can be expressed:
1.) In the
unmodified homozygous frizzled phenotype, every feather is extremely recurved with vanes that are narrow and curled around the rachis; none of the vanes have the normal slightly concaved appearance. The curving of the vanes around the rachis makes the feathers very narrow. This homozygous phenotype imparts a wooly appearance to the bird. The feathers are also brittle and break off easily, over time the fragile state of the feathers produces a bare bird. The wings of the homozygote may contain feathers that are at different stages of growth (Hutt, 1930; Hutt, 1936; Somes, 1990).
2.) In the
unmodified heterozygous frizzled phenotype, many feathers recurve toward the head of the bird while others curve up and away from the body producing feathers that are perpendicular to the bird’s skin. Long thin feathers in the male’s saddle and neck hackles may take on the appearance of a curled ribbon. On the apical end (the end away from the skin) of each deformed feather, small sections of the vanes are twisted and partially curled around the rachis of each feather. The wing feathers (less so in the secondary’s) and outer tail feathers exhibit some frizzling (parts of the vanes tend to curl). The inner tail feathers exhibit less frizzling. This phenotype is much appreciated by the poultry fancier. It is
the phenotype found in frizzle show birds (Hutt, 1930; Hutt, 1936; Somes, 1990).
3.) In some cases, the
modified heterozygous frizzled phenotype looks very much like a non-frizzled phenotype. The modifier inhibits the frizzling allele. In this somewhat normal looking phenotype, the body feathers of the birds exhibit very little recurving or upward curving which is associated with an
unmodified phenotype. The inner tail feathers usually have normal concave vanes and the feathers in the wing are usually normal in appearance. If a bird is believed to be frizzled and is closely examined, a few ruffled feathers can be found on the bird’s neck and the outer tail feathers will exhibit a small amount of vane curling. The curling is found on the inner vane away from the feather’s tip. These signs indicate the bird is
modified heterozygous frizzled (Hutt, 1930; Hutt, 1936; Somes, 1990).
4.) The
modified homozygous frizzled phenotype has a soft and furry appearance; different than the unmodified homozygous frizzle’s wooly look. Each feather is curled. The curling of the vane around the rachis starts away from the end of the feather. The vane at the end of the feather will be narrower but have a more normal appearance. This phenotype is inhibited by the modifier and produces a bird that is different than the unmodified frizzled phenotype (Hutt, 1930; Hutt, 1936; Somes, 1990).
Somes, R.G. Jr., 1990a. Mutations and Major Variants of Plumage and Skin in Chickens.
ed. R.D. Crawford, p.178. Amsterdam:Elsevier
JOURNAL OF GENETICS
Volume 22, Number 1 (1930), 109-127,
The genetics of the fowl
I. The inheritance of frizzled plumage
F. B. Hutt
JOURNAL OF GENETICS
Volume 32, Number 2 (1936), 277-285,
Genetics of the fowl
V. The modified frizzle
F. B. Hutt
