Inheritance of coat colour in the field spaniel dog

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Inheritance of coat colour in the field spaniel dog

R Robinson

To cite this version:

Note

Inheritance of

coat

colour

in the

field

_{spaniel dog}

R

Robinson

St

_{Stephens Nursery, Stephens Road,}

London W13

_SHB,

UK

(Received

22 December 1995;

accepted

13 March

₁₉₉₆₎

Summary - The varieties of the field

spaniel

breed have the coat colours

black,

black and

tan,

liver,

liver and tan; with or without roan colouration.

_{Retrospective analysis}

of litter

data reveals that the colours are

produced by

the

_agouti

mutant alleles solid black

_(As)

and black and tan

(at),

black

_{pigmentation B,}

and liver brown b. Roan colouration is

engendered by

the gene combination spsPTT. The breed is

homozygous

for

long

hair and

the

_long

coat enhances the effect of admixture of

intermingled

coloured and white hairs for the

_variety

known as roan.

dog genetics

/

coat colour

_/

field

_{spaniel / breed}

Résumé - Hérédité de la couleur du _pelage chez le chien Field _Spaniel. Les variétés de la race canine Field

_Spaniel

comprennent les couleurs noir, noir et

_{feu, foie, foie}

et

feu ;

avec ou sans la couleur rouanne. Une

_{analyse rétrospective}

d’observations de

portées

révèle que les couleurs sont dues aux allèles mutants du locus

_Agouti

noir

_uniforme

_(A’)

et noir et

_feu

(a

t

),

au

gène

de la

_pigmentation

noire B et son allèle brun

foie

b. Le rouan

résulte de la combinaison d’un

génotype récessif

pour la

panachure

sPsP et d’un

génotype

homozygote

moucheté TT. La race est

_homozygote

_pour le

_{poil long}

et la

_longueur

du

_poil

renforce

les

_effets

de

_mélange

de

poils

blancs et colorés qui constituent la variété connue sous le nom de rouan.

génétique canine

_/

couleur de robe

_/

Field Spaniel

INTRODUCTION

Although

it is

_possible

to form

_{generalizations}

for the

_heredity

of coat colour in

the

_dog

_(Little,

_1957;

_Robinson,

_1990),

it has become

apparent

as work in the field

has

_progressed

that certain breeds possess

unique

mutant alleles. It is

_important,

therefore,

to

_investigate

the inheritance of colour varieties in individual breeds.

Comparatively recently,

it has been shown that two alleles at the same

_locus,

one

(Willis,

1970; Carver,

1984).

It follows that it is no

_longer

safe to assume that all black

_dogs

are due to the same allele

(Little, 1957).

Even more

recently,

it has been discovered that the

_unique

harlequin

_pattern

of

the Great Dane is

_genetically

different from the merle

_pattern

of other breeds which

it resembles

_{phenotypically}

_(Sponenberg,

_1985;

O’Sullivan and

Robinson,

1989).

Tweed is another colour which resembles merle but which is

_genetically

_unique

to

the Australian

_{Shepherd dog}

_(Sponenberg

and

_Lamoreux,

_1985).

In the

_past,

each of these colours would have been ascribed to the merle gene.

The

_{present report}

describes an

_analysis

of colour variation in the field

_spaniel,

one of several breeds of the

spaniel

_group. The breed is

long

coated and is bred in a

number of different colour varieties. The most common

_variety

is the self-coloured

liver brown. Two less common varieties are the self-black and the black and tan.

In the

_latter,

the whole

_body

is black with tan-coloured

_markings.

These

_comprise

two tan

_patches

on the front of the

_chest,

tan on the inside of the

_legs,

and on the

front of the

_legs

from the

_carpal

to the

_{hock, together}

with two characteristic small

tan

_spots

above the _eyes.

The roan

_variety

is a

_spotted

_animal,

with variable areas of white in the coat

which are

_{liberally interspersed}

with coloured hairs. Each of the

_previous

varieties

may be combined with roan, with

appropriate

changes

for the coloured hairs.

MATERIAL AND METHODS

The

_{investigation proceeded by}

an

analysis

of litters for the

_15-year

period

from

1980 to 1994

_inclusive,

as

_registered

with the British Kennel Club and

_supplemented

by

details of litters for the first half of 1995 and numerous litters from Sweden.

Breeders were consulted in cases of doubt

_regarding

the

_completeness

of litters.

In

_total,

the data consisted of 355 litters

_comprising

1558 _pups; of

these,

74 litters

_provided

evidence of

_segregation

of mutant alleles as summarized in

table I. The

_frequency

of

_phenotypes

_{representing segregation}

of the alleles was

accomplished

by

the a

_priori

method of assessment on the

_assumption

of near or

complete

ascertainment

_{(Emery, 1976).}

This biometric

_{procedure effectively}

allows for the non-detection of litters

_{composed entirely}

of the dominant

_phenotype

from

heterozygous

parents.

The

_completely

black colour behaved as a

_monogenic

dominant to

_liver,

as

evi-denced

_by

the first three entries of table I. The observed

_frequencies

of

_segregation

are in accord with

_expectation,

as shown

by

the

nonsignificant

x2

values.

In

con-firmation of the recessive nature of

_{liver, mating}

of liver to liver gave 1452 liver pups.

The black and tan colouration is

_relatively

uncommon and this is reflected

_by

the small amount of data on this

variety.

However,

it is

_apparent

that the colour

segregated

as recessive to both self-black and self-liver

_(fourth

and fifth entries of

table

_I).

The roan

(spotted)

varieties are

_relatively

more common and the

_segregation

All of the observed

_frequency

segregations

display

close

agreement

with their

expectations

and none of the relevant

x

2

for

_assessing

the

probability

of the

segregations

are

_{statistically significant.}

DISCUSSION

A

_general

_exposition

of the nature and

_heredity

of coat colour in the

_dog

may be

found in Little

₍₁₉₅₇₎

and Robinson

_(1990).

To

_comprehend

the basis of the colour varieties for the field

_spaniel,

it is _necessary to

_briefly

review the

_phenotypes

of the relevant coat-colour mutants.

The solid black colour may be

produced

by

either of two alleles at the

agouti

locus A. These are

(1)

dominant black AS and

(2)

_non-agouti

or recessive black a.

Black and tan

at

is also a member of the

_agouti

series of alleles and is recessive to AS

but dominant to a. Black

_pigmentation

is due to a _gene B which is dominant to its

liver-brown allele b. The colour known as roan is

_{produced by}

a combination of two genes,

piebald

white

_{spotting s}

_P

_,

which is a recessive mutant of

S,

and

_ticking

T. The T _gene induces variable number of coloured hairs in the white areas

_produced

by

the sP _gene. Gene S is

_epistatic

to T.

The

_predominant

colour of the field

_spaniel

is

_liver,

as documented

_by

the

_large

number of inter se liver

_matings

which

_{produced only}

liver progeny. Liver is inherited as recessive to black

_pigmentation

and is due to the well-established b _gene.

The solid black

_variety

could be due to either As or a. Of the

_two,

the AS allele is

indicated because if the colour is due to the a

allele, matings

between black

_parents

could not

_produce

black and tan

_offspring

as shown

_by

table 1.

The

_genotype

of roan

(spotted)

is sPsPTT and the

_segregation

data of table I

relate to _genes S and sP. Gene T is

_only

manifested in the white areas of sP and the

fully

coloured S individuals are

_epistatic

to it. The evidence is that T is

_widespread,

if not

_homozygous,

in the field

_{spaniel population.}

The roan colouration is enhanced

by

the

_long

coat which causes a

_greater

visual random admixture of colours than

if

the

coat is short. The

_phenotype

is termed roan

_by

breeders and is not roan as

strictly

interpreted

as a mixture of

_{coloured/white}

hairs

_throughout

the coat.

Accordingly,

the

_genotypes

of the colour varieties of the field

_spaniel

_may be written as: black

_!-B-s-r-!

liver

_A9

_bbS-T-,

black and tan

a

t

a

t

B-S-T-

and liver and tan

_a

_t

_a

_t

_bbS-T-;

where the dash

_sign

indicates

_possible

_homozygosity

or

_{heterozygosity}

of the recessive allele. Each of the four varieties _may be found

combined with roan when the sP

_replaces

S.

The

_{investigation provided}

some information on the distribution of litter sizes for the breed. The range varied from one to nine _{pups per}

_litter,

with a mean of

4.46 ! 0.11 per litter. The

frequency

distribution was

notably

skewed towards the

smaller litters but without statistical

_{significance.}

ACKNOWLEDGMENT

I

_gratefully

thank P Goodwin who

_{painstakingly}

collected the information which formed the basis of this

_study.

REFERENCES

Carver EA

₍₁₉₈₄₎

Coat colour

_genetics

of the German

shepherd dog.

J Hered 75, 247-253

Emery

AEH

₍₁₉₇₆₎

_Methodology

in Medical Genetics. Churchill

_{Livingstone, Edinburgh,}

37-39

Little CC

₍₁₉₅₇₎

Inheritance

_of

Coat Colour in

_Dogs.

Cornell

_{University Press,}

New York O’Sullivan

N,

Robinson R

₍₁₉₈₉₎

Harlequin

colour in the Great Dane

_dog.

Genetica

78,

215-218

Robinson R

₍₁₉₉₀₎

Genetics

_{for Dog}

Breeders.

_{Pergamon Press,}

Oxford

Sponenberg

DP

₍₁₉₈₅₎

Inheritance of

_harlequin

color in Great Danes. J Hered

_76,

224-225

Sponenberg DP,

Lamoreux ML

₍₁₉₈₅₎

Inheritance of tweed: a modification of

_merle,

in

the Australian

_{Shepherd dog.}

J Hered 79, 303-304