UNDERSTANDING BASIC RAT GENETICS
Basic Genetics
Basic Colors
Basic Genetics:
Before we can delve right into the genetic make up of
your rat, it's necessary to understand a little about
genetics. Thankfully, a great deal of the basic traits are
expressed through simple dominate and recessive genes.
That's great, but what does that mean?
DNA is the basic material that composes who and
what we are. DNA is wound into chromosomes, and
chromosomes are found in pairs inside our cells Rats have
21 pair of chromosomes. When sex cells are produced only
one half of each pair go into each cell, so a sperm would
have 21 individual chromosomes, and an egg would have 21
individual chromosomes as well. When breeding occurs, the
sperm and egg fuse, and the resulting embryo has 21 pairs of
chromosome. One half of each pair the father, and one half
from the mother.
One each chromosome there are many genes. The location
of each gene is called a locus (loci plural) and is
named in the scientific world with a letter such as "x".
There multiple types of possible gene for each locus, and
the different types of gene are called alleles. For
example you may have blue, brown or green eyes. They are
all caused by the gene for eye color, but there are 3
different alleles.
Fortunately, as I have said before, many rat traits are
composed of genes that only have two alleles. . When you
breed two rats, the babies get two alleles of each gene, one
from the mother and one from the father. Each allele may be
either dominate or recessive. With a dominate trait, you
only need one allele present in order to see that trait,
however with a recessive you must have two of the recessive
alleles. We use capital letters to represent the dominate
trait (X) and lower case letters to represent the recessive
one (x).
When you talk about what a rat looks like your referring
to it's phenotype. This is actually how the rat
looks. When you talk about the genes he possesses your
referring to the genotype. This is what he is
genetically. Some rats can be phenotypicly the same while
genotypicaly different. For example an agouti rat can be
either AA or Aa. These rats look exactly the same, but one
of them carries the recessive gene for black.
The actual genotype of a rat is very long as it contains
an allele for every trait even if it is not expressed. A
portion of a solid black rats genotype would look something
like aaGGDDBBCCMMPPRRPePeHH. In order to simplify things we
usually only show the genes that we are interested in;
therefore, when talking about color and referring to a black
rat that didn't carry any other colors we would call him aa
as opposed to that mess above even though they are the same
rat.
Ok, lets look at it with some examples and see if it
makes sense.
Basic Colors:
First of all, all rats are black or agouti based. That
means that if you were to take away all the color
influencing genes, every rat would be either black or
agouti. Most other colors are caused by recessive genes,
that act on or "dilute" the base color. Because they are
recessive, both parents must have at least one of the
recessive alleles in order for the babies to inherit that
color. This is why, when you breed two rats of unrelated
colors (i.e. blue and Siamese), you often get black or
agouti babies.
Because of this, it is necessary to understand the
basics of the colors you wish to work with BEFORE you start
breeding. Otherwise, you could end up with lots and lots of
black rats that nobody wants. (I personally have a soft
spot for solid black rats, but I have found that they are
harder to place.)
All other colors build on these base colors. Agouti
based rats give us our ticked colors (such as fawn and
cinnamon), where as black based rats give us our non ticked
colors (such as beige or mink).
Agouti and Black
American Blue
Russian Blue
Mink and Cinnamon
Fawn and Beige
Champagne and Amber
Pearl Platinum
Siamese and PEW
Agouti and Black:
These traits are represented by the letter "a".
Agouti is the dominate form (A), and black is the
recessive (a). A rat with at least one "A" will be
agouti, where as a black rat must be "aa". When we have
a rat with the dominate phenotype (in this case he's
agouti) but we do not know whether the second allele is
dominate or recessive it may be shown as "A*". The "*"
just states that the other allele is unknown.
This said, when you breed two black based rats
together you will always get black based babies (or non
ticked colors). When breeding agouti rats, it depends
on the second allele. An "AA" rat will produce nothing
but agouti based (or ticked colored) rats, because it
can only donate the dominate allele to it's offspring.
An "Aa" rat could donate either allele and could
potentially have either ticked or non ticked babies.
A* (AA or Aa) = agouti
aa = black
Back to Basic Colors
American Blue (Slate Blue):
Ok, now working on the base color, other genes are
added and act to dilute the color in some fashion. In
this case, the genes that cause American blue are
represented by "g". (Don't ask me, I'm not the one that
chose the letters...lol). The "G" allele is the
dominate one, however this is not the one that causes
the American blue coloring. It is in fact the recessive
allele, "g", that dilutes the base color to American
blue.
Now we know that the base color is either agouti,
A*, or black, aa. When you add two g alleles to these
base colors you get American blue agouti and American
blue, respectively. Because American blue is recessive,
a rat can carry the g allele without expressing it. We
would call this animal an American blue carrier.
There are several ways you can get American blue
when breeding. (In this section when referring to
American blue, I am also including American blue
agouti. The difference is only relative to ticked or
non ticked coats as stated above. When inheriting the g
alleles both will act the same).
The most sure way to get American blue babies is
to breed two American blue parents. Because both
parents are gg, there is no other allele to be donated,
and therefore all babies will be American blue. (one g
comes from the mother and the other g comes from the
father). gg x gg = gg.
You can also breed an American blue to an American
blue carrier. Since the American blue rat is gg and the
carrier is Gg you will get both American blue rats and
rats that aren't. Gg x gg = Gg and gg. Statistically
each baby has a 50% chance of inheriting the American
blue allele from the carrier and therefore being
American blue. The babies that do not inherit the g
allele from the carrier will be carriers themselves as
they must inherit it from the parent that is gg
(American blue).
Finally the third way to get American blue is to
breed two carriers. Each parent my donate either the G
or the g to the offspring. Gg x Gg = GG, Gg, gG or gg.
Therefore, statistically, there is a 25% chance the baby
will be American blue, a 50% chance it will carry
American blue, and a 25% chance that it will neither be
nor carry American blue. The only way to know which of
the non blue babies carries the g allele is to breed
them to a gg rat, Because phenotypicly they will look
just like the GG ones.
When breeding an American blue rat to a rat that
does not carry the g allele, all offspring will be
carriers. gg x GG = Gg.
A*gg = American blue agouti
aagg = American blue
A*Gg = Agouti carrying American blue
aaGg = Black carrying American blue
A*GG = Agouti
aaGG = Black
Back to Basic Colors
Russian Blue:
Russian blue and American blue are genetically
different, and therefore will not produce blue babies
when bred together (unless of course the parents are
carriers of the other type of blue). Unfortunately, not
everyone knows this, and will try to cross the two blues
and be confused when all the babies turn out to be black
or agouti. Again this is because both are just
dilutions of the original base color.
Russian blue is also a simple recessive, and it is
represented by "d", where D is the non dilution allele
and d is the one causing the dilution. It works much
the same as the gg blue does. A dd rat is Russian blue,
a Dd rat is a carrier, and a DD rat neither carries
Russian blue nor is Russian blue.
The breeding possibilities and statistics would be
the same as if breeding American blue. In fact all
simple recessive traits will behave in this same
manner. dd x dd = dd, Dd x dd = Dd, or dd,
Dd x Dd = DD, Dd, dD, and dd, and DD x dd = Dd, and so
on.
A*dd = Russian blue agouti
aadd = Russian blue
A*Dd = Agouti carrying Russian blue
aaDd = Black carrying Russian blue
A*DD = Agouti
aaDD = Black
Back to Basic Colors
Mink and Cinnamon
Cinnamon is simply the agouti based version of
mink. Mink also acts as a simple recessive, and is
represented by the letter "m". M is the non dilution
allele and m is the one causing the base color to be
diluted to mink. Again you can get mink by breeding two
mink rats (mm x mm), a mink rat to a carrier (mm x Mm),
or by breeding two mink carriers (Mm x Mm).
A*mm = Cinnamon
aamm = Mink
A*Mm = Agouti carrying mink
aaMm = Black carrying mink
A*MM = Agouti
aaMM = Black
Back to Basic Colors
Red Eye Dilute
Another very common simple recessive is the red
eye dilute (RED). This is what gives us the colors of
fawn (agouti based) and beige (black based). R is the
letter used where R is dominate and r is recessive. It
is the recessive allele that causes the dilution.
A*rr = Fawn
aarr = Beige
A*Rr = Agouti carrying RED
aaRr = Black carrying RED
A*RR = Agouti
aaRR = Black
Back to Basic Colors
Pink Eye Dilute
Just like RED, the pink eye dilute (PED) is a simple
recessive that dilutes the base color. We represent PED
with the letter "p" where P is the non diluting form,
and p causes the dilution. PED is responsible for amber
(agouti based) and champagne (black based).
A*pp = Amber
aapp = Champagne
A*Pp = Agouti carrying PED
aaPp = Black carrying PED
A*PP = Agouti
aaPP = Black
Back to Basic Colors
Pearl
Pearl works differently than the colors we've looked
at so far. It is multifactorial, meaning that you
need more than just one thing in order to get that
trait. Pearl is expressed in the dominate form, but only
on mink based colors. Using Pe to represent pearl, a
rat must be Pepemm in order to be pearl. When both
dominate pearl alleles are present it is a lethal
combination, and the baby will die before it is born.
Because pearl is dominate, a mink or cinnamon rat cannot
carry pearl. It will either be pearl or not have the
gene at all. This said, because pearl only shows up on
mink, a non mink rat could carry the pearl gene.
When breeding there are several combinations that
could give you pearl. Your best bet is to breed a pearl
rat to a mink based rat (mink or cinnamon). This would
be Pepemm x pepemm. The possible outcomes of this cross
would be Pepemm and pepemm. Each baby would have a 50%
chance of inheriting pearl, and all of them would be
mink based. The only other option would be to breed a
non mink based rat that carries mink and the pearl gene
(PepeMm). This rat would need to be breed to a mink
based rat (mm), or a rat carrying mink (Mm). When you
breed two pearl rats together (Pepe x Pepe) there is a
25% chance for non pearl (pepe), a 50% chance for pearl
(Pepe), and a 25% chance of lethal (PePe).
A*mmPepe = Cinnamon
pearl A*mmPePe = lethal
aammPepe =
Pearl
aammPePe = lethal
A*M*Pepe = Agouti rat carrying pearl
A*M*PePe = lethal
aaM*Pepe = Black rat carrying pearl
aaM*PePe = lethal
A*mmpepe = Cinnamon
aammpepe = Mink
A*M*pepe = Agouti
aaM*pepe = Black
Back to Basic Colors
Platinum
Platinum is also a multifactorial color. In this
case, the color is caused by the combination of two
simple recessive dilutions. You can get platinum one of
two ways, and both involve diluting American blue
farther. This can be done either with mink or with
RED. A mink based platinum would be ggmm while an RED
based platinum would be ggrr. Breeding a mink based
platinum (ggmmRR) to a RED based platinum (ggMMrr)
would simply give you American blue rats that carried
both mink and RED (ggMmRr). Therefore in order to get
platinum, you must know the type of platinum that your
rat is, and breed to a compatible rat. For instance,
you could breed a ggmm platinum to an American blue that
carried mink (ggMm) and have a 50% chance of getting
platinum and a 50% chance of mink.
A*ggmm = Platinum
Agouti A*ggrr =
Platinum Agouti
aaggmm =
Platinum
aaggrr = Platinum
A*ggMm = American blue agouti carrying mink A*ggRr =
American blue agouti carrying RED
aaggMm = American blue carrying mink aaggRr
= American blue carrying RED
A*Ggmm = Cinnamon carrying American blue A*Ggrr =
Fawn carrying American blue
aaGgmm = Mink carrying American blue aaGgrr
= Beige carrying American blue
A*GgMm = Agouti carrying both mink and American
blue A*GGMM = Agouti
aaGgMm = Black carrying both mink and American
blue aaGGMM = Black
A*GgRr = Agouti carrying both RED and American blue
aaGgRr = Black carrying both RED and American blue
Back to Basic Colors
Siamese, Himalayan, and
Pink Eyed White (Albino)
These colors are a bit more complicated. All three are
cause by alleles on the same locus, but in this case
there are three alleles, not just two. C, the non
diluting dominate allele, c, the recessive allele for
albino, and c(h), the recessive allele for Siamese. Ok,
but then where does Himalayan come from? Genes on the C
locus exhibit co-dominace. This means that when
they are present together, neither one is dominate over
the other, but the blend and share their traits. A
Himalayan would be a mix between Siamese and albino (cc(h)).
The two recessive alleles are still inherited the same
way as all other recessives, cc being an albino, c(h)c(h)
being a Siamese. The only difference here is that when
one of each recessive allele is inherited, cc(h), the
resulting baby is Himalayan.
So, if you breed Siamese to Siamese, c(h)c(h) x
c(h)c(h), you will have all Siamese offspring. If you
breed albino to albino, cc x cc, then you will have all
albino babies. Now, when you breed Siamese to albino,
c(h)c(h) x cc, you will get all Himalayan offspring,
cc(h).
One more thing to note. Albino will completely mask
all other traits being carried. Even if the rat were A*ggmmcc,
he would only appear to be albino, the platinum agouti
traits would be entirely hidden. Siamese can be
effected by other color dilutions giving color point
Siamese, such as blue point (American), or Russian blue
point. Himalayans can also have color points.
A*cc = Albino A*c(h)c(h)
= Seal point Siamese
aacc = Albino aac(h)c(h)
= Seal point Siamese
A*Cc = Agouti carrying albino A*Cc(h) = Agouti
carrying Siamese
aaCc = Black carrying albino aaCc(h) = Black
carrying Siamese
A*CC = Agouti A*cc(h) =
Himalayan
aaCC = Black aacc(h) =
Himalayan
Back to Basic Colors
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