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To make
predictions about coat color, or almost any other trait, in cria
from specific breedings you need to understand somebasic rules
of genetics. Coat color is determined by genetics. When people
say something is genetically determined, what they are really
talking about is DNA. DNA is what codes for all of the proteins
(things like hemoglobin, albumin, melanin, insulin, keratin
tissues, hormones all the stuff that make up an alpaca), and for
the instructions on how, when and where to make these proteins
within the alpaca. Segments of DNA that code for proteins are
called genes. Humans have 30,000-40,000 genes and a total of 3
billion base pairs of DNA. In humans, only about 5% of those 3
billion base pairs are protein coding genes, most of the rest is
called “junk DNA” or contains instructions on how, when, and
where to express the proteins inside the body. No one knows yet
how many genes an alpaca has, or how many base pairs of DNA they
have. We do know that like other living creatures, each alpaca
has its own unique DNA sequence that determines many of its
physical characteristics, including its sex and its coat color.
Genes are organized into chromosomes. Alpaca have 37 pairs of
chromosomes (autosomes numbered one to thirty-six plus the sex
chromosomes X and Y). Every alpaca is created by merging 37
chromosomes from its dam’s egg, with 37 chromosomes from the
sire’s sperm during fertilization after a successful mating.
Mutations in the DNA can lead to changes in the proteins that
are made, which may make the proteins work differently or be
expressed differently. DNA also codes for proteins involved in
skin, coat and eye color, fiber shapes and patterns, and aspects
of conformation. DNA codes for virtually every aspect of an
animal.
Genes interact with the environment in many cases to produce the
phenotype that we observe in both people and alpaca. Genes,
however, may behave differently in different environments. Prior
to 50 years ago, very few U.S. Native Americans suffered from
diabetes. Now, after switching to a high-fat Western diet, over
80% of their adult Native Americans in some tribes (like the
Pima) eventually get diabetes. They have the same genes as their
ancestors, but the environment has changed since then (their
diet being part of their environment). Some people believe the
Native Americans were perfectly adapted to a very low fat, low
carbohydrate diet (their traditional diet), and having versions
of genes that cause diabetes on high fat diets, actually help
you survive better on starvation or low fat diets (called the
Thrifty Gene Hypothesis). Many people are aware that alpacas
fiber is influenced by diet. Fiber gets much finer on a near
starvation diet (which is certainly more like their natural diet
in the Andes Mountains, think how many animals actually starve
to death every year!). So genes are a big part of the picture,
but so is environment for many traits.
Each alpaca gets two copies of every gene (called alleles), one
from the dam and one from the sire, but we only see one
phenotype.
A phenotype is what we can observe in the individual (the
expression of the genes), like coat color. This means that both
parents’ genes play important roles in the coat color of the
offspring. Alleles are two different versions of the same gene
that differ by one or more mutations in the DNA. To complicate
things, there are probably at least three genes involved in coat
color, and possibly
additional
genes which can have minor affects on coat color as well. Genes
do not pull or push each other around, as you sometimes hear
breeders say. However some are dominant and some are recessive.
Dominance means that one allele masks the expression of another
allele. For a recessive gene to be expressed you need to this
same gene from both dam and sire. From the ARI registry data, it
seems like black and brown are recessive to white. Fawning may
be an independent gene although it also would appear to be
recessive to white. It would be wonderful if this was the entire
picture, but sadly other genes are very obviously involved that
can really complicate things. There is one gene which appears to
be dominant that influences coat color and pattern. This gene
which goes by many names, we will refer to it as a “white spot”
gene (Sponenberg, 2001). The white-spot gene may have many
alleles which place white fibers on an animal of any color. The
alleles of the white spot gene probably include the patterns
“white face”, “tuxedo”, a white spot anywhere on the body, “all
white”, “blue-eyed-white with and without deafness”, and
possibly some others. Some people suspect multis or patterns are
also part of the white-spot gene. There is just not enough
convincing evidence at this point for or against this idea since
there are relatively few multis around. Here is an example of
how the white spot gene appears to work. If the dam passes on
her white spot allele to her cria, the cria will have a white
spot even if she got the “solid” allele from her sire. So a
white spot allele will mask or override the solid phenotype.
What is really important to know about the white spot gene is
that sometimes two alleles add together to create a new
phenotype. For the white-spot gene, if a cria gets the white
spot gene from the dam and the white-spot gene from the sire,
the cria will be born a blue-eyed white (usually deaf). It is
not known what all the different possible combinations (like
white face and tuxedo, tuxedo and white spot, white spot and
roaning) will produce, but it appears that a number of them can
combine to make blue-eyed whites. Much more research needs to be
done to verify all the possible crosses and their outcomes.
Another
important question concerns grays and the white spot gene. Many
(but not all) gray animals have white faces and often other
white markings with “roaning. Roaning in this case means that
dark and white fibers are mixed together on the same animal”
(what we call silver grey or rose grey in the alpaca industry).
Since this roaning allele appears to be dominant, having just
one copy of any of these alleles leads to a particular phenotype
(ie. you only need to get the roaning allele from one parent for
the offspring to be gray). We will add one more wrinkle to the
white-spot gene story. It is possible that the roaning gene is
not an allele of the white-spot gene, but is a different gene
located very close to the white-spot gene. So close that alleles
of the white spot gene are almost always transmitted together
with specific alleles of a roaning gene since they reside on the
same chromosome. We suspect this might be so because there are
less commonly greys that have no white face or white markings.
It is possible that these greys with no white markings (just
grey fibers distributed throughout the coat alternating with the
natural colored fibers) may not lead to blue-eyed whites. We are
just beginning to collect data on this, and these greys with no
white are often mis-categorized as solids. If you have one of
these greys with no white markings, and have done breedings with
solid and white marked animals, we would love to hear the
outcomes, so please email us about
them. Same for multis; if you have bred animals with three or
more colors that are not greys, we would love to hear about the
breeding outcomes. You can contact us at
andym@binghamton.edu.
Some Example Breeding Outcomes:
To figure out what colors an animal can throw (what alleles an
animal possesses), you need to look at the animal’s dam and
sire, and often the granddams and grandsires and the cria they
have thrown from all of their matings. Let’s start with a simple
example of two solid animals that don’t have white spots. We
also know what colors their parents were and so can determine
what recessive genes might be hiding. We have Vanilla a
beautiful white dam whose mother was white but whose father was
black. We also have Blackie a lovely true black herdsire out of
a true black dam and true black herdsire. Vanilla’s gene’s would
be represented Wb (the dominant white gene from her mother and
the recessive black gene from her father). Blackie’s genes would
be bb having received both recessive genes from both parents.
Some breeders might be afraid that breeding Blackie to Vanilla
might make a black and white pinto. This is extremely unlikely
with two truly solid colored animals (athough white animals can
have white spot alleles, but you cannot see white on white to
detect the pattern). To make predictions you should construct a
Punnet square that shows all the possible alleles each parent
could throw (meaning what alleles could end up in each sperm or
each egg.
Vanilla
W
b
Blackie
b Wb
bb
b
Wb
bb
What this would suggest is about half the time you would get
white animals (who would if bred to black throw black about half
the time) and about half the time you would get black animals.
Data on these breedings from the Australian Registry actually
shows a higher percentage of darker colors than would be
expected. What this likely means is that there are more
influencing genes involved (like the white spot gene) or
diluting genes. Let’s look at an example involving the white
spot gene we won’t worry about coat color yet.
Let's look at
an example involving the white spot gene we won't worry about
coat color yet.
Example with
three alleles from two parents, S=solid no-white markings,
W=white face, R=roaning:
Dam is SW (a white faced animal)
Sire is SR (a grey animal)
Each egg and each sperm only contains one of the two alleles at
random from the parent. So for the sire, half the sperm have the
S allele and half have the R allele. For the dam, half the eggs
have the S allele and half the W allele.
|
Sire |
Dam |
| |
S |
W |
| S |
SS = solid |
SW = White
faced |
| R |
SR = Roaned
(silver) |
RW =
Blue-eyed white (often deaf) |
So,
if you did this cross hundreds of times, it would even out to
25% normal (solid) animals, 25% white faced animals, 25% roaned
(silver) animals, and 25% Blue-eyed white animals that may be
deaf. When you look at data from the registries you actually
seem to get fewer blue-eyed whites that you would expect. Some
have speculated that some combinations of alleles may be lethal
(Paul, 2003) and that pregnancies don't progress to term or are
lost almost immediately after conception. This may explain the
deviations from the expected frequencies in some of the
registries.
Let's look at a more complicated example involving both coat and
the white spot gene. This time a black dam with a white spot
named Spotty is bred to a beautiful silver gray white faced male
named Silverstar. Since Spotty is black and we know black is
recessive, we know her alleles are bb, and since she has a white
face we know she has SW, so her four alleles (from two genes)
are Wsbb. Silverstar's mother was a silver gray and his father
was black. Since silver grays are really blacks with a roaning
gene. Silverstar's alleles are Rsbb.
|
Sire RSbb |
Dam Wsbb |
| Alleles |
Wb |
Wb |
sb |
sb |
| Rb |
RWbb (Blue
Eyed White) |
RWbb (Blue
Eyed White) |
RSbb (Silver
Grey) |
RSbb (Silver
Grey) |
| Rb |
RWbb (Blue
Eyed White) |
RWbb (Blue
Eyed White) |
RSbb (Silver
Grey) |
RSbb (Silver
Grey) |
| sb |
SWbb (White
Spot Black) |
SWbb (White
Spot Black) |
SSbb (Solid
Black) |
SSbb (Solid
Black) |
| sb |
SWbb (White
Spot Black) |
SWbb (White
Spot Black) |
SSbb (Solid
Black) |
SSbb (Solid
Black) |
Of the 16 out comes, 1/4 were
blue-eyed whites, 1/4 were blacks with a white spot, 1/4 were
silver grey, and 1/4 were solid black. Records are not as well
kept for the white spot alleles and many breeders are not
certain why they are getting blue eyed whites. Currently greys
are very popular with US breeders, so that is the one category
we have a fair amount of data to work with. The biggest
difficulty in color genetics research and cria color prediction
is in correctly identifying the phenotype. Color is still quite
arbitrary, and huge numbers of animals are re-classified at
shows by color judges during admission. Coat color changes
during the lifespan as well. Lastly, the white spot alleles may
manifest themselves as tiny dots of white on the lip, in-between
the toes, or other hard to spot places, and many animals are mis-classified
as solids. For the registries, many people do not bother to fill
out the pattern portion when sending in their registration
certificates. Also, as dark animals are often viewed as more
valuable, people tend to err on calling their animal the darker
color (as even ARI guide-
lines suggest). These mis-classifications make figuring out
inheritance much more difficult.
In general, be cautious about
breeding animals with white spot genes together. Certain
combinations certainly seem to produce blue-eyed whites. Sadly
at this point, there is simply not enough data to make
predictions from all the different combinations. For more
information about color genetics, you can also read Merriwether
and Merriwether (2003). We are always interested in general
insight and questions so please feel free to contact us.
Copyright
2003 – All
Merriwether, D. Andrew and Merriwether, Ann M. (2003) Alpaca
color Genetics materials are protected by federal copyrights. Any reproduction or commercial use of these materials without the express written
permission of the authors, is strictly prohibited
by federal copyright law. Merriwether, D. Andrew, and Merriwether,
Ann M. (2003) Alpaca Color Genetics. Alpacas Magazine. Summer,
2003, pp164-168. Paul, Elizabeth (2003) The Alpaca Colour Key,
Erehwon Alpacas. Sponenberg, Phili (2001) Some Educated Guesses
on Color Genetics of Alpacas. The Alpaca Registry Journal, Vol
IV, No1, Spring 2001.
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