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VET 411: Skin > Coat Color Genetics > Flashcards

Coat Color Genetics Flashcards

1
Q

melanocytes

A

pigment producing cells in mammals

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2
Q

what are melanocytes derived from

A

melanoblasts (neural crest cells)

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3
Q

how do genes affect melanocyte distribution in the body

A

controls the number, migration, and survival of melanocytes

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4
Q

where is the first area that white spots will appear

A

periphery
- farthest distance from the neural crest

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5
Q

what are pigments derived from

A

tyrosine

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6
Q

how do pigments get distributed to hair

A

pigments get deposited in granules (melanosomes) that get distributed along the hair shaft

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7
Q

what are the two main pigments

A

pheomelanin
eumelanin

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8
Q

pheomelanin

A

yellow, red, white pigments

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9
Q

eumelanin

A

black pigment

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10
Q

what causes banding pattern of hair

A

timing of pigment distribution during hair growth

banding:
black (eu) –> yellow (pheo) –> black (eu)

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11
Q

what are the two main genetic controllers of pigment

A

MC1R
ASIP

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12
Q

MC1R

A

melanocortin receptor-1

G protein coupled receptor

  1. MSH binds MC1R
  2. MC1R triggers increase in cAMP
  3. signals eumelanin production
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13
Q

ASIP

A

agouti signaling protein

  1. ASIP binds to MC1R and blocks MSH binding
  2. decreases cAMP
  3. signals pheomelanin production
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14
Q

what are the two ASIP transcription promoters

A

ventral promoter
hair cycle promoter

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15
Q

ventral promoter

A

if transcription of ASIP begins at the ventral promoter –> pheomelanin will expressed on ventrum

medium expression: pheomelanin on ventral muzzle, distal limbs, and chest

high expression: pheomelanin everywhere except dorsum

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16
Q

hair cycle promoter

A

if transcription of ASIP begins at the HCP –> pheomelanin will be expressed in a banding pattern across the body

medium expression: banded, dark

high expression: banded, light

17
Q

what are the two ways of getting yellow coat color

A
  1. MC1R loss of function
  2. ASIP gain of function
18
Q

MC1R loss of function

A

yellow

common but recessive

  1. decreased expression of MC1R
  2. no cAMP increase
  3. pheomelanin
19
Q

ASIP gain of function

A

yellow

less common but dominant
(requires increased expression from both promoters)

  1. overexpession of ASIP over entire body
  2. blocks MSH at all MC1R
  3. pheomelanin
20
Q

what are the 3 ways of getting black coat color

A
  1. ASIP loss of function
  2. MC1R gain of function
  3. K locus
21
Q

ASIP loss of function

A

black

more common but recessive

  1. decreased expression of ASIP
  2. no MC1R blockage
  3. eumelanin
22
Q

MC1R gain of function

A

black

least common

  1. MC1R blocks ASIP binding
  2. no MSH block
  3. eumelanin
23
Q

K locus

A

black

MOST common in dogs - dominant

beta defensin mutation (CBD103) prevents ASIP from binding to MCR1
- independent of MC1R and ASIP status

24
Q

how does MC1R status compare to ASIP and K locus status

A

epistatic

if no MC1R present –> will always get PHEOMELANIN because no cAMP signaling

25
Q

what causes albinism

A

tyrosinase mutation leading to absent pigment production

recessive (rare)
pleiotropic - affects eyesight

26
Q

OCA type 1

A

oculocutaneous albinism

caused by tyrosinase mutations

ex. temperature sensitive mutations in siamese cats (white + diluted black areas in cold regions)

27
Q

what causes brown coat color

A

TRP-1 mutation leading to inability to catalyze final step of eumelanin production –> “less intense” black pigment

no pleiotropic effects

28
Q

what causes cream coat color

A

OCA type 4

mutations at MATP or SLC45A2 that disrupts tyrosinase trafficking and proton transport to melanosomes

29
Q

what causes dilute coat color

A

melanophillin mutation that disrupts melanosome transport in melanocytes –> causes clumping of pigment granules leading to dilute color

recessive
bad pleiotropic effects
- lavender foals –> neurologic
- collies –> cyclic neutropenia

30
Q

pleiotropy

A

the production of two or more apparently unrelated effects by a single gene

31
Q

how does white spotting occur

A

mutations that cause failure of melanocytes to reach certain areas/decreased survival

32
Q

dominant white spotting

A

tobiano in horses

33
Q

recessive white spotting

A

white spots in cats, dogs

34
Q

pleiotropic effects of white spotting

A

deafness
- inner ear (stria vascularis) requires melanocytes
- no melanocytes migrating to ear (white ears) –> prone to deafness

35
Q

lethal white foal syndrome

A

overo x overo –> offspring:
- solid
- overo
- overo
- lethal white

foals have ganglionic megacolon leading to colic immediately after birth (inappropriately innervated gut)

concurrent deafness

VET 411: Skin (16 decks)

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