Merle Locus in Dogs

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Merle Locus in Dogs

• Incomplete dominance
• Causes patchy dilutions in coat and eye colors
• Mutation in silver gene (SILV)
• Additive gene
• Normal dogs - mm
• Homozygous MM dogs often have abnormalities
• Deafness
• Blindness
• Small eyes
• Strongly recommended to avoid mating two merles

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Merle Locus in Dogs
Cardigan Welsh Corgiasa asa Mm
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Harlequin Locus in Dogs

• Predominately white with black torn patches
• A dually heterozygous state
• Harlequin (Hh) and merle (Mm)
• Homozygous HH
• Not compatible with life
• Does not breed true
• Only observed in Great Danes

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Harlequin Locus in Dogs
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Spotting Locus in Dogs

• Percent white probably influenced greatly by
  modifier genes
• Molecular genetics still incompletely understood

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Spotting Locus in Dogs (Cont)

• S solid color, no white
• si Irish allele (from Irish rat), few
  definitely spotted areas
• sp piebald 15-20 of coat solid (pigmented)
• sw extreme piebald, virtually no spotting
• i.e. solid white

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Spotting Locus in Dogs

• S 0
• si 1-3
• sp 3-9
• sw 9-10

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Ticking Locus in Dogs

• White areas have flecks of color
• Most dogs are tt

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Ticking Locus in Dogs
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Roan Locus in Dogs
Australian Cattle DogR_

• Disagreement about whether R is a distinct locus
• May represent extreme ticking

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Take Home Points

• All dogs possess various genes which code for
  coat color, texture, etc.
• When breeds do not express a given pattern, the
  normal allele is probably fixed
• Several alleles are lethal or semi-lethal when
  homozygous
• MM, HH
• Breeders should avoid matings that can produce
  lethal homozygotes

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Take Home Points (Cont)

• Be aware of loci important for individual breeds
  which produce desired coat characteristics
  through mating.
• Off color dogs may indicate parentage is
  questionable other factors may also play a role
• Mutation rate, low frequency of recessive allele
• Molecular genetics can provide great insight

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From The Ultimate Dog Book
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Coat Color GeneticsCats

• N. Matthew Ellinwood, D.V.M., Ph.D.
• Spring 2009

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Outline and Expectations

• Be able to list the major loci for genes of
  interest in domestic cats.
• Be able to list the principal alleles at each
  loci.
• Be able to give examples of common cat colors.

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Definition

• Some genes mask the expression of other genes
  just as a fully dominant allele masks the
  expression of its recessive counterpart. The gene
  that masks the phenotypic effect of another gene
  is called the epistatic gene the gene it
  subordinates is the hypostatic gene.

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Coat Color Genetics in Cats

• Primary, recognized genes controlling coat color
• A agouti
• B brown
• C albino
• D - blue dilution
• I - inhibitor
• T - tabby
• O - orange
• W - white

Im blue Not sad, just diluted black.
Similar to dog
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Agouti Locus in Cats

• Agouti color is the color of wild mice and
  rabbits
• Individual hairs contain bands of colors
• Agouti signaling protein

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Agouti Locus in Cats
Agouti
Non-agouti
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Epistasis and aa at Agouti

• Although aa is recessive at the Agouti locus,
  it is epistatic to genes at the tabby locus
• I.E. if you are solid black, you cannot tell what
  kind of stripes you have.
• In this situation, all the alleles at the tabby
  locus are Hypostatic to aa at Agouti
• There is an exception to this we will see later

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Albino Locus in Cats

• Removes successively more pigment
• Tyrosinase
• Darker colored limbs/points
• Thermosensitivity of tyrosinase

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Albinism
Metabolic pathways involving tyrosine.
Phenylalanine is converted to tyrosine by
phenylalanine hydroxylase, the enzyme blocked in
phenylketonuria. Lack of homogentisic acid
oxidase leads to alkaptonuria and deficiency of
tyrosinase to albinism.
http//www.blackwellpublishing.com/korfgenetics/jp
g/300_96dpi/Fig3-5.jpg
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Albino Locus in Cats
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Inhibitor Locus in Cats

• Inhibits the function of pigment
• Unclear where this maps, or what protein is
  involved
• In tabby type of cats, inhibition is most
  prevalent in lighter pigmented areas
• Between the black stripes
• Produces an animal that appears chinchillated
• Previously thought to be due to a chinchilla
  allele at the albino locus

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Inhibitor Locus in Cats

• I Pigment limited to tips of hair strand
• With agouti silver tabby
• With non-agouti smoke
• With orange cameo
• ii Normal

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Inhibitor Locus in Cats
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Brown Locus in Cats

• Brown locus in cats - B, b (TRP1)
• Eumelanin pigment granules in bb cats are smaller
  and more round
• Influences the perceived color
• Little to no effect on phaeomelanin
• bb cats are brown or chestnut
• Not thermosensitive
• Defining characteristic of the Havana Brown

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Havana Brown Cats

• bb at the brown locus
• Tyrosinase Related Protein 1 - TRP1

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Dilution Locus in Cats

• Influences dispersion of pigment granules
• Eumelanin and Phaeomelanin
• Unproven but likely melanophilin
• Black becomes blue or slate
• Yellow becomes cream

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Dilution Locus in Cats
Korat aadd
Cream colored Scottish Fold kitten (left) with
orange littermates A_ddO
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Orange Locus in Cats

• O allele removes all eumelanin (black) pigment
  granules
• Instead, phaeomelanin is produced
• Sex-linked gene
• O allele on X chromosome

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Orange Locus in Cats
Calico aaOoS_
Tortoiseshell aaOoSs
Orange O, OO
Can a male cat have the calico or tortoiseshell
coat pattern/coloration?
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aa As Hypostatic Allele at Agouti

• The action of the orange allele is epistatic to
  the aa genotype at Agouti
• Hence aa can be both epistatic and hypostatic
• Epistatic to the tabby locus
• Cant see stripes if cat is black
• Hypostatic to the orange locus
• aaO_ cats will be orange
• Ceased eumelanin production

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Tabby Locus in Cats

• Principle locus controlling color patterns in
  cats
• Perhaps equivalent to the K locus in dogs

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Tabby Locus in Cats
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Spotting Locus in Cats

• SS white spotting gt ½ body
• Ss white spotting lt ½ body
• ss solid, i.e. no spotting

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Spotting Locus in Cats

• Proposed as an incompletely dominant trait
• SS (6-10)
• Ss (2-5)
• ss (1)

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White Locus in Cats

• White locus believed to be dominant - W
• Not to be confused with
• Excessive spotting SS
• Albino cc

Turkish Van - SS