This document provides an overview of genetics concepts related to cat coat colors, including: - Monohybrid and multiple allele inheritance patterns that determine coat colors like black, dilution, orange. - Co-dominance seen in cremello, albino, and piebald spotting alleles. - Epistasis between orange and black alleles. - Sex-linked inheritance of orange allele. - Pleiotropic effects of genes like white spotting on coat color and hearing. The goal is for students to understand these concepts and predict outcomes of cat breeding crosses.

1. J Corley FDeg

2. Session aims
 To understand about:
 Monohybrid genes
 Multiple alleles
 Co-dominance
 Epistasis
 Sex linked traits
 Pleiotrophy
 To be able to perform crosses, to predict theoretical
outcomes of litters

3. Recap – define the following
 Gene
 Genome / DNA
 Chromosome
 Allele
 Locus
 Dominant
 Recessive
 Heterozygote
 Homozygote
 Monohybrid cross
 Dihybrid cross
 Co dominance

4. History
 Felis catus, generally believed to have been domesticated in
Egypt over 3500 years ago.
 Ancestor likely to be the African wild cat (Felis libyca)
 European wild cat (Felis silvestris) contributed to genetics
of domestic cats by cross breeding with the African wild
cat.
 markingsAnimals Famous For Their Unusual Fur Markings

5. Simple genetics - monohybrid

6. Monohybrid crosses – 1 gene
 Shorthaired allele, L, is dominant to the longhaired
allele, l
 Genotype of a longhaired cat is ll.
 Homozygous recessive (both alleles are the same).
 In a heterozygote (Ll) the the shorthaired allele
dominates over the effect of the recessive longhaired
allele.
 Can infer the genotype of a shorthaired cat by
observing phenotypes of its offspring from mating
with a longhaired cat = a test cross -

7. Test cross
 Do the cross now between a long haired cat, and a
short hair cat
 Possible genotypes for the long haired parent?
 Possible genotypes for the short haired parent?

8. Simple genetics
oftheshorthairedofunknowngenotypetoahomozygousrecessivelonghaired.
Tester Possiblegenotypesofshorthairedphenotype
phenotype genotype Ll ll
longhaired ll 50%longhaired:
50%shorthaired
100%longhaired

9. MULTIPLE ALLELES - BLACK
 Black gene has three alleles, controlling density of
eumelanin granules in the hair.
 Seen in all-black cats, black stripes on a tabby, and the
dark ear-tips, feet and tails (points) of seal point
Siamese.

10. BLACK
 Black allele, B, is dominant, produces black (actually
super-dark brown) coat. Black = B_
 Dark-brown allele, b, reduces black to a dark brown,
chocolate colour. Dark Brown = b_
 Light-brown allele, bl, reduces melanin density even
more, giving a medium brown coat (blbl cinnamon).
 Dominance hierarchy is B > b > bl

11. Task
 What are the offspring of a hetero black cat carrying
brown and a homo chocolate brown cat?
 What are the offspring of a hetero chocolate brown
and a cinnamon cat?
 What are the offspring of a hetero black cat carrying
brown and a cinnamon cat?

12. DILUTE
 Dilute locus has two alleles that affect distribution of
pigment granules in the fur.
 Dominant dense allele, D, produces dense colour
 Recessive dilute allele (d) causes clumping of pigment
granules in the hair shaft, leaving large areas between
clumps with no granules.
 Open areas cause colour dilution

13. Effect of black (eumelanin), orange (phaeomelanin), and
dilute genes on cat coat colors.

14. Co dominance
 Dominance is a continuum
 Runs from completely dominant (e.g. the shorthaired
allele, which completely masks the recessive
longhaired allele) to codominant, where the
heterozygote doesn’t look like either of the
homozygotes.

15. Co dominance - Cremello
 1 dilution

16. Co dominance - Cremello
 2 dilutions

17. What is a white animal?
 White coat and grey skin, any colour eyes = grey
 White coat and pink skin, dark eyes = white
 White coat and pink skin and pink eyes = albino

18. CO DOMINANCE - ALBINO
 Two alleles at the albino locus, pointed, cs, and sepia, cb
 Both alleles are recessive to the full-color allele, C, but
are codominant with each other.
 The homozygous genotype cscs reduces pigment
expression across most of the animal.

19. CO DOMINANCE - ALBINO
 Reduced pigment production in the eyes causes bright
blue eyes
 Reduced pigment density in the hairs turns the coat
from black/brown to a light beige with dark brown
points in the classic Siamese pattern

20. CO DOMINANCE - ALBINO
 Homozygous cb cb genotype has a smaller reduction in
pigment production, turning a black coat to very dark
brown with green or green-gold eyes. (Burmese)

21. CO DOMINANCE - ALBINO
 Heterozygote cb cs gives a combined phenotype called
Tonkinese - a Siamese-patterned coat with darker
base body color and turquoise (aquamarine) eyes.

22. CO DOMINANCE - ALBINO
 All three alleles (C, cs, and cb) are dominant to the
very rare albino alleles, c and ca, which when
homozygous produce white cats with either pale blue
eyes (caca) or unpigmented pink eyes (cc).
 Dominance hierarchy at the albino locus is: C > cb = cs
> ca > c.

23. Task
 What do you expect to get when you cross:
 A pointed Siamese cat with a Burmese cat?
 A Burmese cat with a Tonkinese cat?
 A Siamese cat with a Tonkinese cat?

24. Genotype by Environment Interaction
 The Siamese allele, cs, causes temperature-sensitive
pigment expression
 Allele produces temperature-sensitive tyrosine gene
that is inactive at the cats core body temperature,
leaving a light brown background.
 At the cooler extremities, the enzyme is active,
producing pigment, so forming dark points

25. Genotype by Environment Interaction
 Siamese house cats living in warm homes tend to be
lighter than outdoor cats, which also get darker when
it’s cold
 The cb allele also temperature sensitive, less so than
the cs allele, so produces a darker coat.

26. Epistasis: Gene masking another gene
 The orange gene has two alleles: non- orange and
orange.
 Non-orange allele, o, is recessive and allows full
expression of the black locus.

27. Epistasis: Gene masking another gene
 Dominant orange allele, O, influences expression of
the black and agouti loci - produces red/orange
phaeomelanin instead of black/brown eumelanin.
 Masks the effect of the black gene by converting a
black or brown coat to orange.

28. Task
 What are the expected offspring of crossing:
 A homo orange female with a hetero orange male?
 A hetero orange female with a black male?

29. Sex-linked Traits
 The orange gene is carried on the X chromosome, so is
sex-linked.
 Male cats, can only be black or orange
 Females can be black, orange or tortoiseshell.
 Males are normally XY (heterogametic), so only one
X-chromosome (unless they are Jake, Harry or Eddie).

30. Sex-linked Traits
 If a male carries the orange allele he will be orange (OY).
 Females are XX, so have two X-chromosomes
(homogametic).
 If both chromosomes carry the orange allele, she will be
orange.
 If she is heterozygous (Oo), she will be a patchwork of
orange and black patches

31. Sex-linked Traits
 So the amount of colour produced in female cells is the
same as in male cells, one X-chromosome is
inactivated in every cell in the female embryo.
 For a heterozygous female, some cells produce
phaeomelanin (the active X-chromosome contains the
O allele) and others eumelanin (the active X-
chromosome contains the o allele).
 Which X-chromosome is inactivated is totally random,
producing random tortoiseshell patterns

32. Task
 What are the expected offspring of :
 Crossing a black female with an orange male
 Crossing a tortoiseshell female with a black male?

33. Multiple alleles
 Controlled by more than one gene.
 Cat colour is controlled by multiple genes.
 Can do a test cross to work out the genotype

34. Multiple alleles - Agouti
 Other genes with dominant alleles are:
 the agouti gene - controls colour expression along the
length of each shaft of hair
 the dilute genes, which also influence coat color.

36. AGOUTI
 Hairs with more than one colour band on the hair shaft
 Produce a ticked / agouti coat.
 Typical colour animals (mice, squirrels, rabbits, wolves etc)
 Thought important to crypticity (ability to blend into the
background).
 Determined by the dominant agouti allele, A.
 Non-agouti cats are unbanded, with a solid coloured coat,
if homozygous for the non-agouti allele (aa) at the agouti
locus

37.  Though it looks ‘brown’ it is technically brown and
black banded fur

38. How does it work?
 The ‘agouti gene’ controls where and how brown and
black pigments are set into hair.
 Need to look at how colour is formed in mammal hair.

39. Melanocytes
 At the base of each hair follicle is a melanocyte cell
 Produces pigment and inserts it into the growing hair

40. Hair follicle
Hair
Melanocyte

41. Two types of pigment
 Melanocytes make two types of pigment
 Eumelanin (Browns and blacks)
 Phaeomelanin (Reds and yellows)
 Each relies on a series of pathways before it gets to its
final ‘colour’

42. Pathways
 Melanocyte initially produced ‘Tyrosine’ which is
colourless
 Tyrosine is converted into 5,6 dihydroxyindole,
which is brown
 5,6 dihydroxyindole then converted into eumelanin
which is black
 Similar process happens with phaeomelanin to
produce red/yellow/browns

43. Agouti Gene in action
 As each step produces a different colour, if
any of those steps are disrupted, or broken,
then the fur contain different colours
 The agouti gene controls whether certain
pathways are on or off.
 In the animals seen earlier, the banded fur
is caused by the agouti gene switching the
final brown to black pathway on and off as
the hair grows

44. Tyrosin
e
5,6
dihydroxyindole
Eumelanin

45. Tyrosine 5,6
dihydroxyindole
Eumelani
n

46. Tyrosine 5,6
dihydroxyindole
Eumelanin

47. Task
 What are the offspring of a homo agouti and a hetero
agouti rabbit?
 What are the offspring of two hetero agouti rabbits?
 What are the offspring of a hetero agouti rabbit and a
solid coloured rabbit?

48. MULTIPLE ALLELES - TABBY
 Causes banded (ticked) hairs to alternate with stripes,
blotches, or spots of solid coloured hairs, forming a
stripy pattern
 Two common striping patterns are mackerel (parallel
stripes) or classic (thick stripes or whorls, creating a
blotched pattern).

49. Tabby patterns

50. TABBY
 The stripe pattern is produced by the dominant tabby
allele, T. (TT, Ttb )
 The recessive blotched allele, tb, produces the classic /
blotched pattern (tbtb )
 Abyssinian (Ta) also called ‘ticked’ has faint striping on
the face or tail, and sometimes a dark stripe down the
back.
 Dominance hierarchy is Ta > T > tb.

51. Tabby cats have:
• M on forehead.
• Thin pencil lines on face.
• Black "eyeliner" appearance and white or pale fur
around eyeliner.
• Pigmented lips and paws.
• A pink nose outlined in darker pigment
• Torso, leg, and tail banding. (Torso banding not in the
ticked tabby.)

52. Task
 What offspring will you get from crossing a blotched
tabby with a ticked tabby – all possibilities
 What offspring will you get from crossing a mackerel
tabby with a ticked tabby – all possibilities

53. Effects of agouti and tabby on the black,
dilute and orange gene effects.

54. Pleiotropy
 When a gene affects more than one trait
 Most coat color genes have pleiotropic effects on eye
color.
 Two genes have a pleiotropic effect on coat colour, eye
colour and hearing – dominant white, and piebald
spotting

55. Dominant white
 Dominant white allele, W, overrides all other genes for
pigmentation, producing a white coat and blue eyes.
 Epistatic to all other coat color genes.
 Other genes for colour and pattern present, but hidden as the
dominant white mutation blocks production of melanin by
melanocytes.
 The cochlea in the ear contains a band of melanocytes that
regulate ion balance, necessary for transmission of electrical
signals, stimulated by vibration of the hair cells in the cochlea.
 If the ion balance isn’t maintained, signal transmission to the
brain ceases a few days after birth, causing permanent deafness.
 So dominant white locus is pleiotrophic for coat colour and
hearing.

56. Dominant white

57. Piebald spotting
 Very common.
 Can occur with any coat colour.
 Spotted allele, S, creates white spots, the s allele doesn’t
 So homozygote, ss, has no white spots.
 Heterozygote, Ss, has restricted areas of white spotting;
usually the feet, nose, chest, and belly.
 SS homozygote has white regions covering more than half
the body.
 The white area is the spot, so a spotted (SS) cat can be
completely white!
 Usually follow a regular progression.

58. Piebald spotting

59. Piebald spotting

60. Piebald spotting
 Least spotting = small spots on the breast and belly.
 Increased spotting = covers entire belly, the neck, chin
and front feet.
 Most spotting have spots up the sides, over the back
and onto the head.
 Tail is the last area to have white spots.
 Several genes modify the action of the spotting gene to
produce the continuum of patterns seen in cats

61. Piebald spotting
 Spotted allele, S, also disturbs migration of
melanocytes in embryo development.
 White spots are areas lacking melanocytes.
 Spotted cat shows the same pleiotropy as the
dominant-white gene.
 If spot is over the eye, it will be blue, so spotted cats
may be blue-eyed or odd-eyed.
 If ear is in the spot, cat will be deaf in that ear.
 If spot covers the eye and ear, an odd-eyed cat will be
deaf on the blue-eyed side.

62. Piebald spotting

63. Session aims
 To understand about:
 Monohybrid genes
 Multiple alleles
 Co-dominance
 Epistasis
 Sex linked traits
 Pleiotrophy
 To be able to perform crosses, to predict theoretical
outcomes of litters