Coat Color Genetics Flashcards
What percentage of the mouse coat are overhairs and underhairs? What role does each play in coat color?
Overhairs = 20%. Major role in coat color
Underhairs = 80%. Minor role in coat color
Describe the structure of the different types of overhairs (3) and underhairs (1).
Overhairs:
Monotrich - Guard hairs
Awls - No constriction
Auchenes - Single constriction
Underhairs:
Zigzags - Shorter, with 3 flat constrictions
What are the two types of pigment?
Eumelanin - black
Phaeomelanin - Yellow
What is epistasis in relation to coat color genetics?
Alleles at one locus can obscure or change expression of alleles at other loci.
What are the five basic colors and on which chromosomes are they located?
Agouti (A) - A locus, chromosome 2A
Brown (B) - B locus, chromosome 4
Albino (C) - C locus, chromosome 7
Eye color locus (P) - Chromosome 7
Blue (D) - D locus, chromosome 9
What pigments does the agouti locus control? What is the dominant and recessive colors?
Amount and distribution of phaeomelanin and eumelanin.
A - Agouti. Banding of hair strands
a - Nonagouti. Removes banding. Recessive.
What allele mutations exist for the agouti locus?
A(w) - White bellied agouti. Dominant to A(+)
A(+) - Yellow bellied agouti. Recessive to A(w)
A(y) - Yellow agouti, aka lethal yellow. Homozygotes embryonic lethal. Dominant to everything.
A(vy) - Viable yellow. Associated with obesity.
a(t) - Black and tan. Recessive to A on dorsum. Dominant to A on ventrum
a(e) - Extreme non-agouti. Jet black. Eliminates any yellow strands.
a(x) - Lethal nonagouti. Jet black. Homozygotes embryonic lethal.
What is the B locus also known as?
Brown locus, tyrosinase-related protein 1, Tyrp1
What is the tyrosinase-related protein gene responsible for?
Catalyzes oxidation of dihydroxyindole carboxylic acid. Determines production of eumelanin.
What are the main alleles at the B locus?
Tyrp1(B) - Black. Dominant
Tyrp1(b) - Brown. Recessive. Wild mouse color. Dilutes black to brown.
What allele mutations exist for the B locus?
Tyrp1(B-w) - White based brown, semi-dominant. Causes pigment reduction at hair base
Tyrp1(B-lt) - Light
Tyrp1(b-c) - Cordovan. Reddish-brown
What is the C locus also known as?
Albino locus, tyrosinase, Tyr
What is the tyrosinase gene responsible for?
Catalyzes conversion of tyrosine to DOPA (dihydroxyphenylalanine) and DOPA to DOPA-quinone. Permits or prevents color expression.
What is the structural underpinning of albinism?
Not a lack of melanocytes, but from an alteration of structure of tyrosinase in otherwise normal melanocytes.
What are the main alleles at the C locus?
Tyr (C) or (+) - Color, dominant
Tyr (c) - Albino, recessive. If homo, overrides all other coat color genes. Poor performance on intelligence tests due to visual impairments.
What allele mutations are found at the C locus?
All are recessive.
Tyr(c-ch) - Chinchilla. Reduces agouti and black to silver.
Tyr(c-e) - Extreme dilution (light gray w/ black eyes)
Tyrc-h - Himalayan. White until first molt then dark nose, ears, and feet.
What is the D locus also known as?
Dilute locus, Myo5a.
What is the function of the Myo5a gene?
Non-filament forming unconventional myosin protein. Controls intensity of pigment specified by other genes.
What are the major alleles at the D locus?
Myo5a(+) - No dilution. Dominant
Myo5a(d) - Dilution. Recessive. In non-agouti mice, causes hairs to be blue or blue-black. Dilutes yellow to buff. Linked to short ear gene.
What allele of the D locus is linked to a condition in humans?
Myo5a(d) - Dilution. Model of Griscelli syndrome, where infants have hypopigmented skin and silver-gray hair in infancy.
The D locus only appears on what background?
Tyr(+/+) mice - Those with color
What is the P locus? What gene is responsible, and what is its function?
Pink eye locus. Oca2 gene, a melanosomal transmembrane protein.
What are the major alleles at the Oca2 locus?
Oca2(P) - Normal colored eyes. Dominant.
Oca2(p) - Pink-eyed dilution. Recessive. Also reduces pigmentation of coat - more dramatically in eumelanin than phaeomelanin.
Is an OCA2(p) eyed-mouse the same as an albino?
No. p/p still has small amounts of melanin in the iris and retina.
What are allele mutations at the P locus?
p(d) - Dark pink eye dilution.
What is the Ednrb locus? Where is it found? What is the gene responsible for?
Piebald locus. Enrb gene is responsible for endothelial receptor type B, which controls distribution of coat pigment.
What are the major alleles at the Ednrb locus?
Enrb(+) - No piebald spotting. Dominant.
Enrb(s) - Piebald spotting. Recessive. Distinct white spots with sharp borders. 10% of homos may develop aganglionic megacolon.
Enrb(s-l) - Piebald lethal. Recessive. White with occasional patches of pigmented hairs (usually on head or rump). 100% of homozygotes with eventually succumb to aganglionic megacolon - Model for Hirschsprung disease.
Describe agouti coloration.
Alternating patterns of yellow distal portion of the hair and black proximal portions.
Describe the interaction of agouti protein with alpha-melanocyte stimulating hormone.
Agouti protein A binds alpha-mSH and activates tyrosinase. Activation required to make pheomelanin and eumelanin. Myo5a protein functions to transport pigment to keratinocytes.
