Congenital Baldness
27th October 2011, 2:19 pm
Congenital baldness.
In crested birds, canaries, pigeons, etc.,the crest is a direct inheritance from only one parent. The factor
in the germ cell that causes the development of the crest is what is known as a lethal-dominant factor, which means that when the young bird inherits that factor from one parent it develops a crest,but, when it inherits the same crest-factor from both parents, dies. Thus, no bird having a crest could have gotten the crest-factor from more than one parent, nor could he pass it on to more
than half of his offspring. The factors making up the crest, determining its shape, size, color, etc., are independent of the crest-factor, responsible for the development of the crest.
To illustrate: I once bred some crest-bred (crest-bred birds are those having one crested parent but no crest) Norwich canaries together for a number of generations. Since all of the birds lacked the crest-factor, no crests were produced. Then I mated one of these birds to a small roller with a very scrubby crest. The crested young developed large, Norwich-type crests, proving that the presence of the crest came from one parent, its shape, size, etc., from the other. This means that the crest-factor and the factor responsible for the kind of crest that develops are contained in different chromosomes.*
Now, each crest is composed of two general factors:
One, a rosette of feathers growing out of the top of the head; the other, a bald spot located between the rosette of feathers on the top of the head and the normally placed feathers at the back of the head.
These factors are permanently linked; neither can occur without the other; but the factors governing their relative proportions and development are not linked with the crest-gene, and so can be inherited separately.
If two crested birds are mated together, about one-fourth of the young will inherit the crest-gene from both parents. These birds will be unable to live.
They will either die in the shell or die as the result of ingrown feathers at feathering time.
About one-fourth of the young will receive two genes (factors), one from each parent, governing the size of the rosettes, but only one gene for the development of the crest. These birds can live, and they will develop enormous crests, real mop-heads.
About one-fourth of them will receive one crest-gene, one rosette-gene, but two bald-spot-genes, and in their development the double force of the bald-spot tendency will crowd the rosettes down over the eyes and leave the top of the head bald.
The skin of this bald dome is utterly devoid of the kind of cells from which feathers are grown; so it would be as hard to grow feathers on such a head as it would be for you to grow hair on the palms of your hands, not with standing anything you were told in your youth. The last one-fourth of the babies from our crest-crest mating will fail to receive the crest-gene from either parent.
They will have no crests, but they may receive from one or both parents the genes responsible to the development of good crests
* Note: A chromosome is a small rod-like body in the nucleus of the germ cell. It has been demonstrated that these little rods and the still smaller, dot-like bodies of which they are made up, are the carriers of inheritance
from one generation to the next. The real carriers are the small objects of which the chromosomes are made, called genes. These are so small that they cannot be seen under the most powerful microscopes, but they have
been recently photographed by the use of ultra-violet light.
Different species of animals have different numbers of chromosomes in their cell nuclei. it dies. Thus, no bird having a crest could have gotten the crest-factor from more than one parent, nor could he pass it on to more
than half of his offspring. The factors making up the crest, determining its shape, size, color, etc., are independent of the crest-factor,responsible for the development of the crest.
The perfect line of breeding for crested birds is to mate a
crested bird to a crest-bred bird.
When a crested bird is mated to a bird having no crested
inheritance, part of the young will receive from parent
the crest-gene but will fail to receive, because the other parent does not have them, the genes responsible for a good crest. Some-times these birds have split crests or crests with naked spots in the center. A continuation of this line of breeding will eventually
lead to a strain of bald-headed birds. And these birds, like the ones described above, can never grow feathers on their bald spots
Robert Strouds-Digest
I did not put this in the canary section because I think it applies to Finches also.. FinchG
