Mosaicism is the status of having more than one genetic population of cells in a single individual which develops from a single fertilized egg. This condition can be caused by a spontaneous mutation in a single cell in the developing embryo that leads to the mutation being multiplied every time there is another cell division as the embryo matures, suffusing the fetus with two (or even more) separate genetic populations of cells. It can also be caused by less than robust DNA replication during cell division (mitosis) so that some genes become inactive or are left behind, once again changing the genetic make-up of a population of cells within the embryo. Mosaicism occurs easily due to the millions of cell divisions and possibilities for replication errors that occur during the development of an embryo. In fact, 70-90% of complex organisms (maybe all?) are affected by mosaicism.

Mosaicism can involve any type of chromosome and its genetic apparatus. Some genetic changes of mosaicism are visible, and others are invisible. We generally cannot identify invisible mosaicism without chromosome analysis. In most cases mosaicism does not lead to disabilities, but it sometimes can.

I had an example of visible mosaicism that I didn’t recognize at first in a juvenile Seraph that I thought had the usual red Satinette markings. I didn’t study each feather that carefully in the young bird, but when she molted into adult pure white feathers, I realized she had a single perfectly marked tail feather in blue/black with a perfect white spot. Why did this happen? Sometimes mosaicism can happen in a very tiny patch of tissue – in this case in a single feather follicle. The cells in that follicle lost their functioning Seraph Color Gene Complex during cell division and embryonic growth, reverting back to the original underlying sex-linked base color.

I paired the mosaic hen with the single spotted tail feather with a perfectly marked (pure white) Seraph cock. The first two babies from this pairing were normal Seraphim. Their third baby, however, had a large patch of brown mosaicism on his right wing-shield. Here he is below as a juvenile in molt, showing a brown lacewing pattern in the shield of his right wing where the white-sides and recessive red genes failed to express. He has an entire segment of a wing that is missing the genetic machinery of the Seraph Color Gene Complex. I didn’t notice this when he was a baby as the drab markings didn’t register as being different from the surrounding red feathers he had at the time. The bird to his lower right is the same age and has nearly complete replacement of red feathers in the wing shield and tail with white, as expected, and will soon be completely white as dictated by the Seraphim Color Gene Complex.

The father of this mosaic has sired at least thirty offspring with another perfect white Seraph hen, none of which demonstrated color mosaicism, so the trait seems to have been passed down from the hen. After this mosaic appeared, two more appeared in the same nest, each with a colored tail feather in the exact same position as their mother’s colored tail feather. The hen and the three mosaic babies were taken out of the breeding pool.

There has been some debate as to whether or not mistakes of mosaicism can be passed from generation to generation. Based on my experience with Seraphim and other breeds, I think there is no doubt about it.

The only other Seraph mosaic I had was in 2009. I was new to pigeon breeding and didn’t realize what he was. I sent him to California to a fellow near Sacramento. A year later he called to tell me that a patch of the colored feathers on his left wing did not disappear at either the first molt or the second-year molt as expected. It was only then that I realized the colored feathers were brown, not recessive red, and would never disappear. At the time I advised him to breed the bird, as he was otherwise an amazing specimen, and the standard opinion at the time was that mosaicism wasn’t necessarily inherited, but rather just a genetic accident. Well, that’s wrong. A genetic accident – yes; a non-inheritable trait – no.

If you are breeding Seraphim for show purposes, watch very carefully for evidence of genetic abnormalities and remove anomalous birds from the breeding program, whatever the fault. If you’re raising them for pleasure, such as a backyard aviary, then don’t worry about it.

David Coster