Mosaics

 What is a Mosaic ? 

Is it a Somatic mutation, the result of a Bipaterity sperm or is it simply a Chimera?

Somatic Mutations

 

Somatic mutations are common in plants.  Many of these have been propagated by plant breeders and account for a lot of the plant variations on the market.  Particularly of the plants that do not produce an abundance of seeds or that, produce seeds that are so diverse in their genetic traits that the desired trait is hard to get.  Most of our fruit trees and many of our shade trees are propagated from grafts or cutting to keep the same genetic characteristics.  These usually are propagated from somatic tissue.   Some plants like Coleus are noted for their somatic mutants and easily propagated.  I have seen somatic mutations on lots of plants that produce completely new varieties and thus somatic mutations are converted to new genetic status.    But that is another story since we normally cannot do that with animals. In animals, we see somatic mutations but they are usually not  transmissible by tissue propagation.  However, tissues from these can be grown in the proper medium.  Somatic mutations include moles, warts, cancer, stray colored hairs, stray feathers, etc.. Mosaic areas can occur on varying amounts, sizes, and areas on animals just as they do in plants.  Part of these can be somatic but most are apparently genetic in origin.   The single feather or scattered small patches of feathers can be either genetic or somatic but by definition they are all mosaics. When we see what appears to be a somatic mutant, it many times turns out to be by selection, a genetic mutant.  A couple instances of the latter readily come to mind:  Way back when, a German family was rearing green finches from the Canary Islands, one bird turned up with a single yellow flight feather.  By inbreeding, they were able to increase the yellow feathers until they had an all yellow bird, which is the ancestor of our yellow canaries. A number of years ago, I visited with Elsworth Kistler in Pennsylvania.  He had an Archangel turn up with a white spot about the size of a silver dollar in the middle of its bronze chest.  I saw the bird and tried to buy it from him.  He wanted to breed more of the same and did not want to part with it.  He did this but the white was now about half the bird.  I purchased some of these from him.  Breeding them together, he and I produced some all white with black tails.  Breeding these together produced some all white birds.  When these all white birds were bred back to full colored birds the white completely disappeared so it was a recessive white that acted as a migrational white just as the yellow was a migration mutant in the Canary.

Most somatic mosaics in our birds show up as a small spot or feather on the body.  If you have an ash red bird, a white bird, or an Almond with small spots or feathers other than the color they ought to be (blue or black on red ground) (red on blue ground) etc. they probably are somatic mosaics. Many almonds will have a group of feathers forming a spot somewhere on the body and these are probably somatic. A somatic mutation can occurs in any cell (body cells) except the reproductive cells (genetic cells) i.e. genes on the chromosome which result in the reproductive cells (egg and sperm). In warm blooded animals it is fairly clear cut; unless the trait can be reproduced genetically it is considered to be somatic.  In plants, this becomes blurred because somatic cells, as demonstrated above, can be selected to produce a new plant which can then produce its own reproductive cells and thus the somatic mutation becomes a genetic. In Insects and other cold blooded animals the action of mutations is blurred by the multitude of ways the organism can be, and is, affected by the environment in the very broad sense.  Many insects can reproduce parthenogenically until the environmental conditions become stressful and then reproduce genetically.   Many mollusks and annelids reproduce by being hermaphroditic.  Some mollusks are born female and after a number of years change to males so that sexual reproduction can be accomplished.  Some fish may change sex in the absence of available males in the population.  Alligators and Crocks reproduce sexually but the sex of the hatchling is dependent upon the temperature of the eggs during incubation.   All of these things have a bearing upon the picture as to whether a mutation in an organism can be called somatic or not.   As you can see there is no simple answer.  Bet you did not want to know all of this when you asked. Keep up the good work.  Dr. Lester P Gibson.

Next we will look at Ken Davis's report on the infamous Two-Sider.  A very strange and interesting specimen indeed.  I'm sure you will find Ken's article interesting reading.  It is based on Dr. Hollanders Bipaterity theory; which as I pointed out above is no longer excepted science .   I am however going to including it here, as a window to the past.  It shows how our understanding of things have changed over time; as we progress in both our knowledge and our understanding of genetics.    Just try and keep in mind, that where Ken refers to this Two-Sider bird as being "Bi-Paternity" (formed two sperms and one egg) it is in actuality a Chimera; which is formed from two separately fertilized gametes placed on a single yolk and subsequently become fused together into one individual.   A Chimera is formed when two fertilized eggs fuse into one body shortly after the first few cell divisions or very closely thereafter.  The earlier the fusion takes place the more complete the two side differences are.   In this instance it must have been very early in development.

Marvin Lee of Praire Grove, Ar. bred this bird which was genetically a sooty, blue bar, baldhead roller on one side and a black homozygous Chinese owl on the other.    The fact that this specimen is of two different breeds, and involves more than just the sex chromosomes is all the more evidence that it is a chimera.   Dr. Gibson has the body of this bird preserved.  What follows is an article written by Ken Davis.   Ken was a close student of the late Dr. Willard F Hollander, a professor of genetics who first put forward the theory of two sperms fertilizing a single egg as one way to create this type of mosaic.  Dr. Hollander specialized in the study of bird, mice and fruit fly genetics.  He loved his pigeons and was without a doubt the most knowledgeable expert on their genetic make up.  The vast majority of what we know about pigeon genetics comes from him.  Sadly he passed away and we can no longer ask him for guidance in our studies.  So lets now turn to Ken's article for a look into the past for what was once considered its cause.  

The infamous two-sider 

Mosaic By Ken Davis Yes indeedy, that "two-sider" is a nice mosaic, for sure. But, something more. If you look at the photo's real close you'll see that the birds right side is a spread Chinese Owl, complete with the Frill, the Pantaloon, Owl shaped head, etc... Look at the head-on view.....notice the difference in feet structure, leg structure and length, the total package? Now, the left side of the pigeon appears to be a blue bar Birmingham Roller....but look close....and......in fact.....you will see.....it is a Chinese Owl/Birmingham Roller hybrid! In fact, the whole bird is a Chinese Owl/Birmingham Roller hybrid. "How can that be", you ask? Well I had Doc on the phone for about an hour the other day, and we discussed this individual......I'll hi-light for you: Now, I saw this pigeon at the Oklahoma National in January, along with a thousand other Fanciers. I took many photographs of the bird, (most of which I sent to Doc). I was allowed to handle the pigeon, and I talked with the breeder of the pigeon. He told me the circumstances of how this bird came to be, but I couldn't remember. Well, he told Paul Gibson the same thing, and Paul told it to Doc, and Doc in turn refreshed my memory while we were on the phone. The breeder, (and his Dad), are from Arkansas. They breed flying Birmingham Rollers and Exhibition Chinese Owls. Now, they had all the cocks and hens separated at the time. A hen snuck out of the hen pen, and into the neighboring cock pen, which housed spread Chinese Owl cocks and Brown Bar (true Brown) Birmingham Roller cocks. O.K., now, we were all going over these pictures the other night at the Genetics Meeting at Joe Fraziers Place, and Leon Stephens told us that he knows how this happened; that it was "Bi-Paternity". He said that the Frill and the Pantaloon on the Owl side of the bird are recessive characteristics, so the Mother of this mosaic had to be a Chinese Owl, and was bred by two cocks, a spread Chinese Owl cock and a blue series Birmingham Roller, therefore the mosaic was Sired by two Fathers, hence the "Bi-Paternity".

Well, this ain't what happened! The hen that snuck into the cock pen was a "Brown Bar Birmingham Roller", and she was left in there, or allowed to stay, and she was THE ONLY HEN IN THERE. Now, Frill and Pantaloon being recessive characteristics, how'd they get there? How can they express? Let's address the color part of it. The mosaic individual is spread blue on it's right side, and blue bar on it's left side. Now, the Dam, or Mother to this individual is a true Brown Bar, and she could only have been bred by true Brown Bar Birmingham Roller cocks and spread blue Chinese Owl cocks. Well, if she was "treaded" by both, ("Bi-Paternity"), the mosaic would have been a Brown Bar Birmingham Roller on one side, and a spread blue Chinese Owl on the other side. But it's not! Careful examination of this mosaic reveals that it is phenotypically a "pure" Chinese Owl/spread blue on it's right side, and a Chinese Owl/Birmingham Roller blue bar hybrid on it's left side. So how can this be? The best explanation is "Super Numerary Sperm". That is to say that the Brown Bar Birmingham Roller Dam was bred by a Spread Blue Chinese Owl cock, and that more than one sperm from the Sire penetrated the ovum. And for reasons not totally yet understood, the extra spermatozoa affected the phenotype to the results which we now see. Just this last week, Doc sent me a copy of a paper, "PIGEONS IN GENETICS, FROM DARWIN TO BIPATERNITY", which he sent to Edinborough this past February for publication. In it there is a section titled "LATER PERIOD", and here Doc writes about his beginnings of his studies on mosaicism. He states: "One of the most puzzling genetically phenomena was masochism, which did not seem to be like that in Drosophila. Carl Graefe of Ohio presented me with a mosaic female, basically of wild-type color but with a large yellow patch. Yellow is produced by the combination of autosomal recessive red and sex-linked dilution, also a recessive. The bird's pedigree had neither of those genes, and breeding test with a yellow male produced no progeny showing them. Simultaneous somatic mutation was an extremely improbable explanation. Then Graefe mentioned that the mosaic had been produced in a flock pen, in which yellow males were also present. This fact suggested that the yellow patch might have derived from a different sperm than that producing the zygote. Such an explanation was supported by the early embryology of pigeons--Harper (one of Whitman's students) had observed that polyspermy is a normal feature." Now, this next line is important, so pay attention, and read it over several times....."The extra sperms form an accessory cleavage ring around the zygotic cleavage. I proposed the term bipaternity, and it seems to be to account for most sectoral mosaics in pigeons,".....here comes another very important part.....read it carefully......."though 2 fathers are not generally necessary to provide differences among sperms. A similar explanation is used to account for gynandromorphs in honey bees, and is termed androgenesis." PIGEONS IN GENETICS, FROM DARWIN TO BIPATERNITY, By W.F.HOLLANDER, Professor Emeritus of Genetics, Iowa State University, Ames, Iowa50011. This paper issued at the Department Zoology/Genetics, Iowa State University, February 2001. Not copyrighted

Mosaic Duplication So how will a mosaic, be it from a somatic mutation or the formation of a chimera, reproduce?  Will it produce more of the same or will it be one form or the other?   When talking about mosaic pigeons, this is a frequent question asked. Reproduction of the same mosaic effect, regardless if it is for structure or color depends on the DNA within of the cells of the gonads.  In the case of a somatic mosaic you most likely will not be able to duplicate the mosaic effect since the mutation took place outside of the gonads and therefore no DNA there will reflect that difference.  Chimera mosaics are different.  With a Chimera it is possible  for one gonad to be of one grouping of DNA while the other contains the other grouping of DNA.  So in general the bird may indeed be able to pass along both forms of structure or both forms of color differences  to their offspring but not both possibilities from both gonads at the same time to a single gamete.   Remember a single gamete originates from a single gonad.  So your only going to have that gonads DNA passed along to the youngster.  Never a combination of both.

 A mosaic of Mosaic photos

all of which are Chimeras.

        
Five Mosaic photos by Michael Spadoni of Geelong Australia

Half Smoky / Blue bar by AL Neese  and a Half Mealy / Grizzle by Larry Davis

 
These two photos of the same bird were taken by David M. Longseth at the 2003 NYBS.
The right wing shield is a blue check while the left side is a dark 'dun/brown' color with heavy black flecks or sootiness. 
This left side may be almond as the sire was an almond bird.