Essai tra 4

~ Wild-Type, Mutation, Natural Selection & Evolution ~
When studying pigeon genetics, one of the most important concepts we need to comprehend is wild-
type. In order to study the mutant traits, we choose the most common phenotype from a population
of organisms that represents the rest of that population. It is just a standard phenotype which we test
against other mutations. The actual expression of those genes found in wild-type’s genotype
produces a set of observable characteristics in the wild-type’s phenotype. The designation of wild-
type is based upon a numerical representation or estimation of the standard in a population. Although
living things seldom express the absolute perfection outlined in a standard, they can be compared to
one.
The ancestor to our domestic pigeons, the rock-pigeon (Columba livia), is considered to be the wild-
type, the standard against which we judge everything. The Scientific name "Columba" is the Latin
word for dove or pigeon; "livia" means blue or blue-gray color. Columba livia originated in Africa,
Asia, Europe, and the Middle East. They arrived in North America with European settlers in the 17th-century for food and religious
purposes. Because rock-doves in North America (and other continents) are from populations established by escaped domestic pigeons, we
refer to them as feral pigeons. The term "wild" is reserved for pigeon populations that were never domesticated and still live in their native
habitats - various open and semi-open environments such as cliffs and rock ledges which are used for roosting and breeding in the wild.
In pigeon genetics, the wild-type we use is commonly known as blue bar with a clean head - free from any head crest and has clean red
pigmented legs - free from any leg feathers. Although we don’t have the exact measurements of all the phenotypic traits of the wild-type
that traces back 150 years to use as a standard for everything, for color and a few other things it is very well defined. It does not have, for
example, any heavy skin above the beak or around the eyes like the Barbs, Carrier Pigeons, and Kings do. They have a dark bluish-gray
head, neck, and chest with glossy greenish, and reddish-purple iridescence along its neck and wing feathers. The neck and crop feathers are
dark, with much iridescence. The adult female is almost identical to the male, but the iridescence on the neck is less intense and more
restricted to the rear and sides, while that on the breast is often very obscure. Young birds show little lustre and are duller. The iris of the
eye is red at the margin and yellow centrally, giving an orange appearance. The beak and the claws are very dark brown and black. For
feather ornaments wild-type is defined as lack of feather ornaments (not frilled, fantailed, crested, has sideburns, longer neck feathers to
cover its head completely like in Jacobins or Capuchines, etc.). The plumage is basically a light bluish gray; the remiges become black
distally, and the ends of the rectrices also show black distally but in the form of a broad band with a faint bluish terminal edge. The tertiary
wing feathers exhibit a black area in the vanes, as do secondary coverts and often the median coverts; these two rows of black areas form

two black bars across the closed wing. The rump and under wing feathers are albescent or whitish terminally; the outer vanes of the outer
rectrices are also albescent. Wild-type has 12 rigid tail feathers with a clearly distinguished dark area at the end of the tail known as the
“sub-terminal tail band”. The name “albescent” was given by W. F. Hollander for those areas to distinguish from whiteness due to complete
absence of melanin such as in white flights. Only the tail feathers on each side of the tail have the albescent strip on the outside, running
from the base of the feather almost to the tail bar.
We also know that wild-type has oil (preen) gland above the base of their tail,
although not all domesticated pigeon breeds have oil glands. This gland
secretes oil when the pigeon grooms itself, thus spreading this oil over its
feathers. This oil contains a compound that produces vitamin D when
exposed to the sun’s ultraviolet rays. So, as the pigeons grooms under an
ultraviolet light source, it’s actually mixing up a healthy batch of vitamin D
on its feathers. Reports suggest that in general birds with extra tail feathers do
lack the gland above their tails; however, no one knows why. Our current
understanding of pigeon vision suggests that we don’t have the slightest
evidence of enhanced vision in wild-type compared to other mutants.
Although we don’t have any detailed explanation of why almond mutation is
causing eye problems, Carl Graefe reported highly pigmented almonds did
not seem to have many eye problems compared to almonds with lack of the
pigment in their feathers. In addition, we don’t have any clue about the
smelling ability of Columba livia or any of the mutant breeds. A few day-old
wild-type squabs have a ring around their beak, just behind the tip, which
lasts about a week after the chick was hatched. The rest of the beak is sort of
flesh colored and not highly pigmented. However, if any of the darkener
genes (mutations) are present in the genotype the whole beak gets pigmented,
and the beak ring does not show. Up to five or seven days of age the legs of
the wild-type should be flesh colored and show no pigment at all. After that
age, leg color will start to very slowly turn red. If any of the the darkener
genes are present in their genotype, the leg color turns brownish-blackish.
Newly hatched squabs also have distinct down colors, length and amount.
Although we don’t have any quantitative reports, there is a claim that cocks

have a different color down than hens do. However, there is a lot of variation in down colors from near white to quite orange. Newly
hatched wild-type squabs considered to be normal down.
We also have well defined behaviors of the wild-type. For voice, wild-type has the normal coo, and it is not equipped to sing like
Trumpeters. For sexual behavior, wild-type is the normal behavior and not the exaggerated behavior we would see in birds like Spanish
Thief Pouters. Flying pattern is also well defined where they fly in a range of height and distance from their home. They don’t have
specialized mutations to roll, tumble, or hover like Sky Cutters, dive like Dewlaps, find home from long distances like Homers, or fly in
other acrobatic patterns like Doneks and Kelebeks. They are not able to fly long hours like the high flying breeds averaging 10 hours or
more flight time.
There are claims about Columba livia having magnetite in their beaks and brains for them to use Earth’s magnetic power to navigate.
However, we have no clue which genes control this trait, and the standard amount of magnetite found in wild-type vs. homing pigeons is
unknown. We currently don’t have any data about their blood type system or immune system genes to establish a standard either.
The genetic symbol for every gene in wild-type is the plus sign (+), representing everything pertaining to a wild-type pigeon. As you get
familiar with distinct genes and their symbols you will notice that we don’t have a symbol for all the distinct traits. So far, we have done a
fair job of characterizing traits that only involve one mutant gene which are mainly color mutations. There are some color mutants that
involve several genes and we haven’t been able to isolate and characterize a single one of those mutants yet. The assignment of symbols
does not occur until someone publishes data that is reproducible, sensible, and statically valid. We know that all traits are controlled by
genes and we normally assign meaningful symbols to the mutated genes: al for albino, Od for dominant opal, b for brown C for checker, cr
for crest, d for dilute, etc. In the case of wild-type, we assume that we do not know which genes control which traits, even though we can
observe that wild-type has orange eyes, bluish body with two black bars and black sub-terminal tail band, etc. We are not allowed to give
genotypical names to wild-type genes, since it is our standard. Therefore, we assign the wild-type symbol (+) to every gene in every locus.

It is imperative to understand that phenotype of the wild-type is the result
of all the genes acting together to produce what we observe in a wild-type
Columba livia. Every single gene that makes the wild-type must be present
and function properly for us to see all the characteristics of a wild-type
phenotype. Thus, no particular gene found in wild-type’s genotype is
special; they are all equally important and necessary.
If any of the wild-type genes are broken (mutated) the whole bird is not
going to function in a wild state as well as with a wild-type gene. In a
mutated pigeon, the phenotypic difference may be small and may not even
be visible to naked eye, but it will be real. It is not necessary to identify
each of thousands of genes but only to know that the affect from the entire
genome package all together produces a wild-type phenotype. It should
then be obvious to observe which genes are affected to cause the
mutations on an otherwise wild-type phenotypes. This way, the
descriptions can be reduced to deviations from the standard. The mutant gene responsible for a deviation becomes the center of attention
and a standard of reference minimizes the chance of mistakes in interpreting the results of breeding tests. Wild-type helps us understand the
connection between presence or absence of a genetic trait in an individual.
We are assuming there is a wild-type gene at every locus on every chromosome in our standard Columba livia and any change affecting the
function of any gene is called an allele at that location. These changes can be recessive, dominant or co-dominant and might be tightly or
loosely linked to another locus. The phenotypic trait we observe may be and usually is dependent on more than one gene, or series of genes.
We know that the mutated gene located at the dilute locus causes ash-yellow plumage if the wild-type gene at the ash-red locus is also
mutated. When multiple mutated genes are present in a genotype, an interaction is apparently taking place and we get an ash-yellow
plumage. Similarly, all the wild-type genes must be present and interact together to produce the wild-type phenotype. By adding a single
mutant gene, e.g., dilution (d) to a female's genotype, the bird's phenotype is diluted in color (some fanciers call this phenotype "silver").
We can often identify the affect of a single mutant gene on a wild-type plumage - as well as on other mutants we've identified, e.g., dilute-
brown (two mutants).
A pigeon that has wild-type genes in every loci of every chromosome is nearly impossible to get, as we don’t even have the sequencing of
pigeon genome on hand to compare and identify which sequence codes for wild-type in any given locus. Then the question should arise how
do we know if the mutation we are testing is actually tested against the true wild-type? From a practical standpoint, we do not even have a

half decent source of wild-type to use as standards, so we do the best we can to find a bird that is very close to wild-type. In addition, in
order to test a mutation, the wild-type bird we are testing against does not need to have wild-type gene in every single locus. Hollander
pointed out repeatedly that we need to use a bird that is reasonably wild-type for the traits we are testing. Suppose we are testing grouse
(feathered feet) against wild-type to see if it is dominant, recessive, or co-dominant. We can literally use any pigeon of any color (doesn’t
have to be a blue bar) as long as the bird we are testing has clean legs like the wild-type and does not carry grouse mutant in its genotype
(heterozygous for grouse). The same goes for beak crest, side burns, shell crest, etc. Therefore, we can use any bird that is wild-type for the
particular mutation we are testing as long the bird does not carry that mutant gene in heterozygous state. It does not generally matter at all if
the bird is far from wild-type in traits that are not under study. Now, if we are testing a color mutation, then we have to use a blue bar.
However, it doesn’t matter if the blue bar (wild-type) has muffs, crest, pearl eyes, or fantail, etc. In other words, there is no reason at all to
avoid using an ash-red, spread Tumbler Pigeon with a colored rump, that has muffs and has a shell crest in a study of tail feather count.
You might be wondering why we need a standard. According to Richard Cryberg, PhD, standards are simply picked and defined so that
everyone uses the same thing; so, we can talk to each other and make sense. When studying genetics we choose a standard because it allows
two people to talk about genetics without wasting all of their time defining the standard they are using every time they talk to a new person.
Rock Pigeons display many variations among their numbers scattered throughout the world. The argument rages on yet, as to whether the
earliest forms were barred or checkered. Why did they choose the blue bar phenotype as the wild-type in pigeons? Could they have chosen
blue check as the wild-type instead? Or could they have chosen ash-red barless or spread black or any other common phenotype as our
standard? The answer is “yes”. So, why did they choose the blue bar and not the check? The answer is very simple: whoever first defines
the standard in any given species, whichever phenotype he/she chooses becomes the wild-type for that particular species.
In the 13th edition of Systema Naturea, Linnaeus Tom I.2 (1789), the author Gmelin has become the first person to describe the phenotype
of the Rock Pigeon (the ancestor of our domestic pigeons) and named it Columba livia. He described it as ash-grey with a white rump and a
black bar on the tail and wings, (“cinerea, uropygio albo, alurum fascia, caudaeque apice nigricante”). Gmelin knew the Rock Pigeon was
the ancestor to domesticated pigeons, and the domestication took place more than four thousand years before Gmelin described the wild-
type. According to Gmelin, the most important difference between the domestica (domesticated pigeons) and the livia (wild-type blue-gray
pigeon), was the double bar on the wings (“alarum fascia duplici”). Because Gmelin was the first person to describe the phenotype of
Columba livia, the genotype became the wild-type in pigeons--the median against which everything is judged. The rock pigeon/dove is the
overwhelming choice that gave rise to modern pigeons. Plumage varies widely across the world, but the white-rumped blue bar is the
phenotype that was selected, and it became our standard.
“It is sometimes difficult to decide what is normal. In the absence of a known wild-type one can use logic to help decide. For example, in
cattle, horns to defend against predators or just in dominance conflicts are more likely than the absence of horns. Or the preponderant