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Transcript
Coat Color Genetics
Coat color patterns are created by
genes. Genes carry the genetic codes
that create a horse’s size,
conformation and color. Let’s
continue to learn how genes create
coat colors.
The Reason Behind the Coat Pattern
• Genetic inheritance determines a Paint’s coat pattern.
What is genetic inheritance? It is the genes (genetic
codes) parents pass on to their offspring.
• Why is this important? It is important for Paint Horse
breeders to understand genetic inheritance so they can
breed for certain coat patterns, possibly raising the
value of their horses.
• What does a gene do? Genes transfer the genetic
information from a parent to its offspring, determining
the appearance of the offspring—including the coat
color and pattern.
What are Genes?
• Genes
– Genes are the tiny, basic units
of inheritance found in DNA.
– Genes determine color, size,
and make-up for every living
species.
– Each equine species receives
half of their genes from their
sire (father) and half from their
dam (mother).
– Physically, genes are linked
together like a strand of pearls
to form a chromosome.
What are Chromosomes?
• Chromosomes
– Chromosomes are made up of
genes.
– Every Paint Horse has 64
chromosomes.
– Each chromosome was initially
created through fertilization,
where genetic information
from the sire (father) was
united with genetic
information from the dam
(mother).
– Loci and Alleles are also found
on chromosomes.
Loci
Alleles
Actual photo
What are Loci?
• Loci
– The different points or markers
along a chromosome.
– Loci are like street signs in a
busy city, allowing us to find
our way along a complex
chromosome.
– At a specific locus, scientists
can locate certain genes. These
genes appear at that locus for
every individual of that
species.
– At one locus there can be two
Alleles
Loci are numbered.
This depicts a
chromosome half.
What are Alleles?
• Alleles
– Two alleles are found at each loci on a chromosome.
– Alleles code for the different ways a gene can be
expressed.
– For example, consider your eye color. You have a loci
on a chromosome for eye color. At that loci there are
two alleles—one from your mother and one from your
father. The dominant of the two alleles is the eye color
that you display. This is your phenotype (the eye color
seen). The genetic classification (what we can’t see but
what is on the loci) is called the genotype.
Dilution Genes
• There are five currently known dilution genes: Cream, Champagne,
Dun, Pearl and Silver.
• Champage, Dun, and Silver are dominant, meaning that a horse need
only have one in order to have the characteristic diluted coat pattern.
Whether the horse is heterozygous or homozygous for champagne, dun, or
silver, the dilution effect is the same. (Without genetic testing, these colors
are problematic to breed for, since you cannot tell from the horse's
appearance whether or not it will pass the color on to offspring. Only
homozygous horses will pass on the color pattern to 100% of offspring)
• Cream is an "incomplete dominant" which means that the dilution effect
is stronger with two doses (homozygous, two cream genes, one from each
parent) than if the horse has only one (from one parent - heterozygous). A
single copy of Cream produces palominos, buckskins and smoky blacks
(depending on the base coat that is being diluted). Two doses of Cream
produce cremellos, perlinos and smoky creams.
• Pearl (known in Quarter Horses as "Barlink") is recessive, or perhaps
an incomplete recessive; In order to take effect, the Pearl gene needs to be
either homozygous, (2 genes - both genes on the pair being Pearl) or
heterozygous (1) in accompaniment with another dilution gene, such as
Cream or Champagne. Some people say they can discern a slight effect
with just one copy, so Pearl may be an incomplete recessive.
Chestnut (ee)
• All horses have either the black or chestnut
gene
Black (EE or Ee)
• All horses have either the black or chestnut
gene
Bay (AA or Aa)
• This agouti allele isolates the black on a
black horse to the points (legs, mane, tail)
Gray (GG or Gg)
• Born with a normal or almost normal coat
color and they progressively get more white
as they age
• The skin and eyes remain dark
Roan (RNrn)
• RNRN is a lethal gene
• The head and leg colors on roan horses are
like those of solid colored horses
White (Ww)
• Pink skin with dark eyes
• This masks all other genes
• WW is a lethal white gene
Champagne (ChCh or
NCh)
• Champagne with red base
• Champagne with bay base
» Champagne with
black base
Dun (DD or Dd)
• Dun with red base
=red dun
• Dun with black base
= grullo
Dun with
bay base
Silver (ZZ or Zz)
• Silver with bay base
• Silver on black base
» Silver with red base has no effect
Cream – 1 copy of gene
cr
(Cc )
• Palomino=cream on red base
• Buckskin=cream on bay base
• Smoky black=cream on black base
Cream - 2 copies of gene
cr
(c
cr
c )
• Cremello=2 cream genes with red base
• Perlino=2 cream genes with bay base
• Smoky cream=2 cream genes with black base
Pearl (PrlPrl or NPrl and
• Pearl on liver chestnut
• Pearl with cream on red base
• Pearl with cream on black base
cr)
c
The Paint Horse
• Paint Horses are a unique
breed known for beautiful
and colorful coat patterns.
• The base coat color can be
any color in the equine
spectrum.
• Superimposed over the
base color are white
spotting patterns.
Paint Horse Color Patterns
• Tobiano: white markings usually cross the back
between the withers and tail.
• Overo: white markings usually do not cross the
back between the withers and tail.
– Frame Overo
– Sabino
– Splashed White
• Tovero: a combination of the Tobiano and Overo
coat patterns.
How are these unique coat patterns created?
Tobiano (TOTO or TOto)
Overo (Oo)
OO is lethal in the early embryonic stages
Tovero
Piebald
Skewbald
• Black with white
• Any color other than black
with white
Sabino
Splashed white
Appaloosas (LPLP or LPlp)
• Leopard
Blanket
Varnish Roan
Snowflake
Frosted
Let’s Review
• What are Paint Horses known for?
Answer: Paints are known for their unique coat
patterns.
• What are genes?
Answer: Genes are tiny units of inheritance found in
DNA that code for the make-up of an individual.
• What makes up a chromosome?
Answer: Genes make up chromosomes, loci are
found on chromosomes and alleles are found at
loci.
Let’s Review
• What is the title given to specific parts along a
chromosome where two alleles are found?
Answer: Loci
• Why are there two alleles at each loci?
Answer: Two alleles are at each loci because the
offspring receives one from its mother and one
from its father.
• What is genotype?
Answer: The genotype is the genetic material that we
can’t see expressed on the outside of an
individual, such as a recessive allele.
Let’s Review
• What is phenotype?
Answer: The phenotype is the physical appearance
of an individual, a characteristic that we see, such
as that determined by a dominant allele.
• In simple dominance, what allele will be
expressed?
Answer: The dominant allele is expressed in simple
dominance.
• If I have a heterozygous pair of alleles, what
genotype do I have?
Answer: I have one dominant allele and one
recessive allele.
Great job! You have completed
Part 1 of Coat Color Genetics!
You may test your knowledge with the quiz
available at www.apha.com/education.
This presentation has been provided courtesy of the American Paint Horse
Association.