The Crest....

Crest was one of the first traits which I recognized as belonging to the Malayoid back in 1985. It is generally considered monstrous, a deleterious mutation, reaching it's full expression in breeds like the Polish.

In these birds it is always associated with a bulbous cerebral hernia and a very reduced duplex comb, also known as 'V-shaped' or 'horn' comb.

[ Picture by Ralph G. Somes, Jr., Chap. 6 of Poultry Breeding and Genetics, R. D. Crawford, Editor ]

According to Dr. Hutt, pg. 127 (1949), "It was pointed out by Tegetmeier (1856) that in the skulls of crested fowls the cranium is vaulted, sometimes forming a great tuberosity in which lie the cerebral hemispheres of the brain. The underlying cause of this abnormality was shown by Krautwald (1910) to be an excessive accumulation of fluid in the brain. It fills the third and fourth ventricles and thus causes an upthrusting of the cerebral hemispheres and of the frontal bones which overlie them. The cerebellum lies back on the medulla instead of up toward the hemispheres, and the latter are elongated."

"As a result of these abnormalities, chicks severely affected show at hatching varying degrees of cerebral hernia recognizable by enlargement of the skull and often detectable by palpation. The frontal bones are raised at the posterior and interior borders. As the chick grows, ossification proceeds in the membranes of the fronto-parietal region. In mature fowl the brain is completely encased, but the roof of the cranium is perforated with holes of various sizes. These are less evident in the oldest birds."

"Just how these abnormalities cause the elongation and erection of the feathers that form the crest is not clear, but since the size of the crest is directly proportional to the extent of the abnormalities in the cranium and in the brain, there can be no doubt that the latter do cause the crest. Krautwald found the skin underlying the crest to be thickened and highly vascularized, conditions which could affect the activity of the feather follicles."

[ Illustration by Arthur O. Schilling from the The American Standard of Perfection ]

It is controlled be a single autosomal dominant gene. I reasoned that perhaps this character would take on a more natural appearance in a breed more like the Malayoid such as the Cornish. I found this to be the case, particularly in the hen, although herniated individuals continue to show up.

This hen has a natural crest, no cerebral hernia. Also has a cushion comb and 'beard and muff' traits. She is half Dark Cornish Bantam.

This is a good case of where the breeding shows me things I wouldn't know otherwise. Just because the Malayoid and the Red Jungle Fowl had compatible genomes doesn't mean that the individual traits would necessarily express the same way in the hybrid.

These are full sibs of my own breeding. The chick on the left has a herniated cranium while the chick on the right does not.



References:

Hutt, F. B. 1949. Genetics of the Fowl. pg 127.

Krautwald, F. 1910. "Die Haube der Huhner end Enten. Ihre Ursache, Entatehung und Vererbung." Inaugural Dissertation, zootech. u veterinar. Institut, Universitat Bern.

Tegetmeier, W. B. 1856. On the remarkable peculiarities existing in the skulls of the feather-crested variety of the domestic fowl, now known as the Polish. Proc. Zool. Soc. London, 1856: 366-368.