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| Coat Color Genetics |
Have you ever wondered how we can predict what color puppies will be born in a litter of Labradors? Questioned how two
black parents can produce yellow or chocolate offspring? This is the page that will answer your questions. First, let's talk a
bit about basic genetics. (Click here to skip to the Color Prediction Charts.)
A "gene" is a specific combination of DNA on a chromosome that codes for a certain trait. It may control the size of your
earlobes, the thickness of your hair, or in our case, the color of fur. Some traits are controlled by more than one gene - they
are called polygenetic traits.
Each gene is made up of two alleles. One is inherited from each parent. There may be many different alleles for each gene
that exist in a species. For example, there is an allele each for blue eyes, brown eyes, green eyes, hazel eyes, etc - but you
only end up with two - one from each parent.
The expression of a gene is determined by the dominance of the particular alleles. When one allele expresses even in the
presence of a different second allele, it is considered dominant. For example, brown eyes are dominant over blue eyes - so if
you inherit a brown eye allele from your mother, and a blue eye allele from your father, your eyes will be brown. The blue
eyed allele is considered 'recessive' because it requires two copies in order to be expressed. For some traits, expression is
more complicated than that, but for the purpose of our conversation, this is all you need to know.
Coat color in Labradors is controlled primarily by two genes. One genes contains alleles for either black or chocolate fur.
The other gene is what controls the expression of yellow fur color.. First, let's consider the two genes separately -then we
will talk about how they work together. The gene that controls black or chocolate is called the "B" locus. Since we already
know that each dog can have only two alleles for each gene, we can figure out that, at the B locus, a Lab will have alleles
that are either black, chocolate, or one of each. Black is dominant to chocolate, so that means if he has one chocolate allele
and one black allele, he will appear black in color. Labs require two chocolate alleles in order to express chocolate colored
fur. Labs with only one recessive chocolate allele are said to 'carry' chocolate, or be 'chocolate-factored' , because they can
pass it on to their offspring, even though they do not appear chocolate themselves.
At the site of the yellow gene, known as the "E" locus, the dog will have alleles that are either 'on' for yellow, or 'off' for
yellow. There are no other color alleles associated with this gene. The dog must have two 'on' yellow alleles in order to
express yellow colored fur.. Because two 'on' alleles are needed, they are considered recessive to the 'off' alleles. (By the
way, yellow ranges from white all the way to fox red. These are all still considered yellow and are controlled by the yellow
gene. The darkness of yellow is actually controlled by other genes called amplifiers, but we won't get into that. It's enough to
know that yellow varies in shade, but it's technically still yellow).Labs with only one 'on' yellow gene are said to be carriers of
the yellow gene, because they can pass it on to their offspring, even though they do not appear yellow themselves.
Wait a minute! Hold on here. How can a dog be black or chocolate AND yellow at the same time???
They can't. It turns out that the yellow gene is a 'masking' gene- that means, when it is expressed, it over-rules the
expression of the other gene (black or chocolate). So your dog could have chocolate alleles, but the two yellow alleles will be
expressed instead. However, if your dog has only one or zero 'on' yellow alleles, the color from the other gene (black or
chocolate) will be what you see.
In genetic terms, each allele is given a letter. Lower case letters are used to indicate recessive alleles, and upper case letter
are used for dominant alleles. In labs, B is used to denote dominant black, and b is used for the recessive allele of chocolate
(B of course was chosen because the gene is at the B locus).Yellow, at the E locus, is denoted by E for 'off' yellow, which is
dominant to e - 'on' yellow. Every lab will have two alleles at the B gene and two at the E gene. For example, let's consider
Ruger - his genetic color coding would look like EEBB. He has two 'off' yellow alleles, and two dominant black alleles. He
appears black in color. Onyx is another black Lab, but her color coding is a little more complex - EeBb. She has one 'off'
yellow allele, one 'on' yellow allele, one Black allele, and once chocolate allele. She is black in appearance because B black
is dominant to b chocolate, and the yellow masking gene is not activated because only one allele is 'on'.
So why do we care? Knowing what the genetic code of your dog is allow you to predict what color puppies they will have
when mated with another dog of a known genetic code. The genetic coding (ie. EeBb) is called the 'genotype' of the dog -how
they actually look (black, chocolate or yellow) is called the phenotype. If you know the genotype of your dog, it can help you
predict what the phenotype of the puppies will be. It will also give you a clue as to what the phenotype of his parents might
have been, if this is unknown.
Below are the different colors of labradors and their possible genotypes. You should be able to see why I abandoned art in
favor of a career in science.
black parents can produce yellow or chocolate offspring? This is the page that will answer your questions. First, let's talk a
bit about basic genetics. (Click here to skip to the Color Prediction Charts.)
A "gene" is a specific combination of DNA on a chromosome that codes for a certain trait. It may control the size of your
earlobes, the thickness of your hair, or in our case, the color of fur. Some traits are controlled by more than one gene - they
are called polygenetic traits.
Each gene is made up of two alleles. One is inherited from each parent. There may be many different alleles for each gene
that exist in a species. For example, there is an allele each for blue eyes, brown eyes, green eyes, hazel eyes, etc - but you
only end up with two - one from each parent.
The expression of a gene is determined by the dominance of the particular alleles. When one allele expresses even in the
presence of a different second allele, it is considered dominant. For example, brown eyes are dominant over blue eyes - so if
you inherit a brown eye allele from your mother, and a blue eye allele from your father, your eyes will be brown. The blue
eyed allele is considered 'recessive' because it requires two copies in order to be expressed. For some traits, expression is
more complicated than that, but for the purpose of our conversation, this is all you need to know.
Coat color in Labradors is controlled primarily by two genes. One genes contains alleles for either black or chocolate fur.
The other gene is what controls the expression of yellow fur color.. First, let's consider the two genes separately -then we
will talk about how they work together. The gene that controls black or chocolate is called the "B" locus. Since we already
know that each dog can have only two alleles for each gene, we can figure out that, at the B locus, a Lab will have alleles
that are either black, chocolate, or one of each. Black is dominant to chocolate, so that means if he has one chocolate allele
and one black allele, he will appear black in color. Labs require two chocolate alleles in order to express chocolate colored
fur. Labs with only one recessive chocolate allele are said to 'carry' chocolate, or be 'chocolate-factored' , because they can
pass it on to their offspring, even though they do not appear chocolate themselves.
At the site of the yellow gene, known as the "E" locus, the dog will have alleles that are either 'on' for yellow, or 'off' for
yellow. There are no other color alleles associated with this gene. The dog must have two 'on' yellow alleles in order to
express yellow colored fur.. Because two 'on' alleles are needed, they are considered recessive to the 'off' alleles. (By the
way, yellow ranges from white all the way to fox red. These are all still considered yellow and are controlled by the yellow
gene. The darkness of yellow is actually controlled by other genes called amplifiers, but we won't get into that. It's enough to
know that yellow varies in shade, but it's technically still yellow).Labs with only one 'on' yellow gene are said to be carriers of
the yellow gene, because they can pass it on to their offspring, even though they do not appear yellow themselves.
Wait a minute! Hold on here. How can a dog be black or chocolate AND yellow at the same time???
They can't. It turns out that the yellow gene is a 'masking' gene- that means, when it is expressed, it over-rules the
expression of the other gene (black or chocolate). So your dog could have chocolate alleles, but the two yellow alleles will be
expressed instead. However, if your dog has only one or zero 'on' yellow alleles, the color from the other gene (black or
chocolate) will be what you see.
In genetic terms, each allele is given a letter. Lower case letters are used to indicate recessive alleles, and upper case letter
are used for dominant alleles. In labs, B is used to denote dominant black, and b is used for the recessive allele of chocolate
(B of course was chosen because the gene is at the B locus).Yellow, at the E locus, is denoted by E for 'off' yellow, which is
dominant to e - 'on' yellow. Every lab will have two alleles at the B gene and two at the E gene. For example, let's consider
Ruger - his genetic color coding would look like EEBB. He has two 'off' yellow alleles, and two dominant black alleles. He
appears black in color. Onyx is another black Lab, but her color coding is a little more complex - EeBb. She has one 'off'
yellow allele, one 'on' yellow allele, one Black allele, and once chocolate allele. She is black in appearance because B black
is dominant to b chocolate, and the yellow masking gene is not activated because only one allele is 'on'.
So why do we care? Knowing what the genetic code of your dog is allow you to predict what color puppies they will have
when mated with another dog of a known genetic code. The genetic coding (ie. EeBb) is called the 'genotype' of the dog -how
they actually look (black, chocolate or yellow) is called the phenotype. If you know the genotype of your dog, it can help you
predict what the phenotype of the puppies will be. It will also give you a clue as to what the phenotype of his parents might
have been, if this is unknown.
Below are the different colors of labradors and their possible genotypes. You should be able to see why I abandoned art in
favor of a career in science.
Pigmentation refers to the color of the dogs skin, particularly on their nose and around their eyes. Black labs always have
black pigment. Chocolate Labs always have chocolate pigment. But yellow labs may have either, depending on the alleles
they carry at the B gene site.
Yellow labs with at least one Black allele will have black pigment (because it is dominant). Yellow labs who have two b
chocolate alleles will have brown pigment. They are referred to as dudley, and it is undesirable, although it doesn't really
affect them in any meaningful way outside of the show ring. Dudley labradors will have brown squares on their nose for the
purposes of the diagrams above to denote theirbrown pigment.
Carriers are dogs who 'carry' a recessive allele but do not express it themselves. In the diagrams above, we picture carrier
dogs by having a box of a different color located in their belly.
The Punnett Square
The Punnett Square is a simple tool used to predict in what combinations alleles will be inherited. Let's look at an example.
Keep in mind that each puppy gets ONE allele for each gene from each parent, for a total of two alleles for each gene.
In our example, we will breed a handsome tri-factored black lab to a yellow lab. The genotypes for each parent would be
EeBb and eeBB respectively. The first thing we need to do is figure out, for each parent, the different combinations of alleles
that could be inherited. Let's start with dad.
Puppies could get the yellow 'off' allele paired with the Black allele ------- EB
They could get yellow 'off' paired with chocolate allele -------------------------Eb
They may end up with yellow 'on' and Black ---------------------------------------eB
or they could get yellow 'on' and choclolate ----------------------------------------eb
Mom's turn - she is yellow, with a genotype of eeBB
As you can see, there is only one possible combination of alleles from mom --------------eB
Now, we build our Punnett Square. It's like a multiplication table for geneticists. Along the top, let's plug
in the alllele combinations that could be inherited from the stud dog. The left hand column is for the
dam's alleles.
Next, we figure out what will happen when each puppy inherits their alleles from mom and dad.
So, for this particular matchup, we will be expecting 25% Black puppies who carry yellow, 25% Black puppies who carry
yellow and chocolate, 25% yellow puppies, and 25% yellow puppies who carry chocolate. Naturally, every litter does not
come out in these exact proportions, but it does give you a good idea of what to expected. Notice that even though the sire is
tri-factored, he did not produce any chocolate puppies because the dam does not carry a chocolate allele that can be
passed down.
Click HERE to see a comprehensive matchup of all possible litter combinations, and their results. This took a long time to
produce, so please do not copy it onto your website. Feel free to link to our page if you would like to show your visitors this
information. THIS is a link to Dr. Sheila Shmutz coat color page. She is THE professor of coat color whom I was lucky to study
under, and who has done much of the genetic research to determine the information I've shared above.
black pigment. Chocolate Labs always have chocolate pigment. But yellow labs may have either, depending on the alleles
they carry at the B gene site.
Yellow labs with at least one Black allele will have black pigment (because it is dominant). Yellow labs who have two b
chocolate alleles will have brown pigment. They are referred to as dudley, and it is undesirable, although it doesn't really
affect them in any meaningful way outside of the show ring. Dudley labradors will have brown squares on their nose for the
purposes of the diagrams above to denote theirbrown pigment.
Carriers are dogs who 'carry' a recessive allele but do not express it themselves. In the diagrams above, we picture carrier
dogs by having a box of a different color located in their belly.
The Punnett Square
The Punnett Square is a simple tool used to predict in what combinations alleles will be inherited. Let's look at an example.
Keep in mind that each puppy gets ONE allele for each gene from each parent, for a total of two alleles for each gene.
In our example, we will breed a handsome tri-factored black lab to a yellow lab. The genotypes for each parent would be
EeBb and eeBB respectively. The first thing we need to do is figure out, for each parent, the different combinations of alleles
that could be inherited. Let's start with dad.
Puppies could get the yellow 'off' allele paired with the Black allele ------- EB
They could get yellow 'off' paired with chocolate allele -------------------------Eb
They may end up with yellow 'on' and Black ---------------------------------------eB
or they could get yellow 'on' and choclolate ----------------------------------------eb
Mom's turn - she is yellow, with a genotype of eeBB
As you can see, there is only one possible combination of alleles from mom --------------eB
Now, we build our Punnett Square. It's like a multiplication table for geneticists. Along the top, let's plug
in the alllele combinations that could be inherited from the stud dog. The left hand column is for the
dam's alleles.
Next, we figure out what will happen when each puppy inherits their alleles from mom and dad.
So, for this particular matchup, we will be expecting 25% Black puppies who carry yellow, 25% Black puppies who carry
yellow and chocolate, 25% yellow puppies, and 25% yellow puppies who carry chocolate. Naturally, every litter does not
come out in these exact proportions, but it does give you a good idea of what to expected. Notice that even though the sire is
tri-factored, he did not produce any chocolate puppies because the dam does not carry a chocolate allele that can be
passed down.
Click HERE to see a comprehensive matchup of all possible litter combinations, and their results. This took a long time to
produce, so please do not copy it onto your website. Feel free to link to our page if you would like to show your visitors this
information. THIS is a link to Dr. Sheila Shmutz coat color page. She is THE professor of coat color whom I was lucky to study
under, and who has done much of the genetic research to determine the information I've shared above.
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