Download Evaluation Guide for Dog Phenotypes

Evaluation Guide for Dog Phenotypes
To evaluate a dog’s genetically controlled traits, you need to know what
phenotypes it shows. This list of standard questions is adapted from
Alderton’s “Dogs” (Alderton, 1993). It is a quick yet complete overview of all
the major phenotypes that can identify specific characteristics reliably and
consistently.
Not all questions need to be answered; many single-gene phenotypes (which
are marked) can be identified by a single question.
General Physical Features
1. What is the dog’s height (measured at the dog’s withers
(shoulders))?
Generally:
• Large and extra-large dogs are >24 inches
• Medium dogs are 18-24 inches
• Small dogs are <18 inches.
Small overall size in dogs has been linked to specific alleles for several genes
that decrease IGF-1 signaling in some way. The opposite has not been
reported - IGF-1 is not over-active in large dogs. (Sutter, 2007).
Size Differences in dogs. 1. Dogs have the most extreme within-species
variation of any mammal, as shown by this wolfhound and chihuahua. 2. A
great Dane, an example of a large breed. 3. Airedale, and example of a
medium sized breed. 4. Pomeranian, a small breed. Pomeranians are small
as a result of reduced IGF-1 activity.
2. How is the dog’s head shaped?
• Nose is long, skull narrow (Jack Russell terrier, afghan hound,
greyhound)
• Skull shape is average (i.e., wolf-like) (German shepherd, golden
retriever)
• Skull is strongly rounded, with a relatively short nose (Chihuahua,
beagle, Labrador retriever, chow)
• Skull is angular, square, or blocky (Mastiff, St. Bernard, rottweiler)
• Nose is strongly blunted or tucked under the skull (brachycephalic)
(Pug, bulldog, Boston terrier, boxer)
Brachycephaly has been tentatively linked to either a single gene or small
group of genes. In general though, head shape appears to be a multi-gene
trait. (Bannasch, 2010; Schoenebeck, 2012; Schoenebeck, 2013).
Differences in head shapes: German Shepherd (1), Golden Lab (2),
Rottweiler (3), and Bulldog (4).
3. Does the dog have long or short legs? (Single gene)
• Legs are about as long as the overall body length (wild type seen in
most dogs)
• Legs are much shorter that overall body length (Dachshunds, basset
hounds)
Foreshortened limbs in dogs is a form of chondroplastic dwarfism. It is the
result of an autosomal dominant allele, specifically an expressed FGF-4
retrogene. (Parker, 2009)
This is a comparison of long versus short legs. The Beagle (1) has long legs
whereas the Daschund (2) has foreshortened legs.
4. What is the coat structure and texture?
• Overall hair length on back and ribs: short vs. long (Single gene)
• Hair texture: flat (also called smooth), fluffy, or wiry (Single gene)
• Undercoat (soft hairs beneath a heavier topcoat): present or absent
• Hair is straight versus curly (Single gene)
Coat length is controlled by FGF5, while coat texture is controlled by Rspondin 2 and keratin-71 (Cadieu, 2009).
A comparison of some of the different coat structures and textures. The
Beagle (1) has short straight hair, the schnauzer (2) has short wiry hair, the
husky (3) has long straight hair and a double coat, and the puli (4) has long,
curly hair.
5. Does the dog’s face have a mustache or extended eyebrows (also
called furnishings)? (Single gene)
• Absent (most dogs)
• Present (schnauzers, shih tzus)
Furnishings are controlled by R-spondin-2 (Cadieu, 2009).
The Beagle (1) has no furnishings like most dogs, whereas the Schnauzer
(2) has a mustache and extended eyebrows.
6. What is the natural shape (not docked or altered) of the ears?
• Overall size relative to head?
• Position? (Hanging versus erect; straight versus folded)
As of 2013, evidence suggests ear shape is controlled by multiple genes.
(Boyko, 2010)
A comparison of various dog ears. The Beagle ear (a) is neatly folded near
the head. The Basset hound ear (b) is draping and pendulous (like a
curtain), and the husky ear (c) is pointed and held erect.
7. What is the natural structure of the tail (not docked or altered)?
• Length relative to torso length?
• Relative curl? (On scale of 1 (straight like a beagle) to 5 (tightly curled
like a spitz))
• Decoration: plain (beagle, Labrador retriever) or feathered, with hair
hanging beneath it (setters and gun dogs)?
Tail length and curl are both multi-gene traits (Boyko, 2010).
A comparison of several dog tail structures. The Beagle (a) has a straight
tail, the Setter (b) has feathered tail, and the Husky (c) has a curled tail.
Coat and Eye Color
Inheritance of coat color is more difficult to understand and map out
because multiple interacting genes are involved. However, the relevant
genes still follow well-defined inheritance rules. If you learn and understand
the cell biology underlying coat colors first, the inheritance patterns make
more sense.
The questions below help you categorize general color reliably. To analyze
coat color in detail, use the handout Evaluating Coat Colors.
8. Which basic coat colors are present?
A dog's coat color can have up to 6 distinct “major pigment colors”. These
are:
1. Pure black
2. Milk chocolate brown
3. Various shades of gray (slate or blue-gray, neutral gray, or browngrey in color; pale silver to charcoal grey in intensity)
4. Yellow (ranges from very pale cream to fawn gold, or deep brownorange)
5. Red (ranges from pale peach to dark red, or red-brown (liver colored))
6. Pure white (i.e., absence of pigment)
A comparison of the six major pigment colors in dogs. (1) a black
Schippperke. (2) a brown (chocolate) Labrador retriever. (3) a grey
Weimaraner. (4) a yellow Labrador Retriever. (5) a red Setter. (6) a white
Samoyed.
9. Is the coat one color, or many colors? If many, which color
predominates?
When trying to decide which is the dominant color, focus on a dog’s back
and ribcage behind its front legs. In general the color on a dog's chest,
head, feet, and tail is less consistent, both for genetic and non-genetic
reasons. The reasons for this will be explained elsewhere.
A tri-colored rough-coated collie. This collie is predominately black on its
back and shoulders. The yellow borders and a white underside are secondary
colors.
10. Are individual hairs multi-colored?
• No; individual hairs are one solid color for their entire length
• Yes; individual hairs change color from base to tip.
Having individual hairs that have alternating bands of eumelanin
(black/grey/chocolate brown color) and pheomelanin (blond/yellow/red
color) is called an agouti phenotype. Agouti coloration is controlled by a
single gene, but it can be covered up by other genes.
A comparison of coats with banded agouti hairs (1) versus yellow hairs (2).
11. Are both eyes the same color?
• Yes; both eyes blue, or both eyes brown
• No; one eye is blue, the other brown.
Typically dogs have two differently colored eyes when they are heterozygous
for a specific allele of the merle gene, but it can occur for other reasons.
Dogs that have 2 blue eyes are not usually homozygous for the allele; their
blue eyes are controlled by other genes.