Alpaca Colour Genetics

Transcription

1 Dr Kylie Munyard Colourbration 27 th August 2016

2 Research Trying to understand the inheritance patterns and molecular causes of colour in alpacas Using Mendelian genetics principles, molecular genetics techniques, and phenotype Developed a basic model that describes some of the colour variation seen in alpacas Many, many more questions without answers yet!

3 What is Colour? Mammals can only produce two types of pigment Yellow and Black

4 Genes & Alleles Every alpaca has the same genes e.g. Agouti MC1R Every alpaca has two copies of each gene These two copies can be the same or different

5 Genes & Alleles Each different version of a gene is called an allele A single gene can have one or many alleles E.g. Agouti has four alleles in horses Alleles can be dominant, neutral or recessive MC1R dominant MC1R neutral MC1R recessive

6 Colour Genetics Alpaca colour can be thought of as having two separate but interacting parts: Base colour and Pattern There are two main genes that control the base colour: MC1R and Agouti There are several genes that control pattern Any base colour can co-exist with any pattern, more than one pattern, or none of the patterns

7 Brown? Scientifically the term brown describes a colour that is caused by a defect in black pigment production It makes black pigment look brown It does not affect yellow pigment The causative variant is in the Tyrp1 gene The brown allele is recessive The wild-type (black) allele is dominant

8 Source: Kaelin & Barsh 2013

9

10 Brown?: Pigment 0.7 Total Amount Melanin of Pigment (A 500/mg) White L/Fawn Fawn L/Brown Brown D Brown Red Brown Black Brown Black

11 Brown?: Pigment Ratio of Yellow A 650 to /A Black 500 pigment 0.5 Slide about melanin data from Rhys A 500 /mg Amount of pigment Dog Samples Light Brown Brown Dark Brown Red Brown Dalmations Labradors Poodles Springers

12 Brown?: Pigment Amount of Yellow pigment Amount of Black pigment

13 Brown?: Tyrp1

14 Brown: Conclusions Brown probably doesn t exist in alpacas Perhaps milky brown or brown points? So, what do they have? White & fawn alpacas have small amounts of yellow pigment Brown, dark brown and black brown alpacas have mixed yellow and black pigment Black alpacas have mostly black pigment

15 Base Colour: Agouti Alpacas have four Agouti alleles The most dominant agouti variant: Fawn White to fawn The next most dominant variant: Bay Tan/ brown/ red-brown body with black on the extremities

16 Base Colour: Agouti Third allele: Black & Tan Produces a black body with tan on the undersides The reverse of bay The most recessive agouti variant is: black Produces solid black

17 Base Colour: Agouti All animals with an Agouti base colour have black skin regardless of the colour of their fibre Agouti variants are probably responsible for most colours in alpacas There is a range of colour intensity for each variant These four alleles can occur in 10 different combinations

18 Combinations

19 Combinations

20 Combinations

21 Combination

22 DNA Identity The exact DNA sequence for is unknown Three DNA mutations are known for &

23 Base Colour: MC1R Mc1r either allows or prevents the production of black pigment Mc1r has two alleles in alpacas The neutral allele Allows ASIP alleles to be expressed normally The recessive or non-functional allele Prevents expression of black pigment

24 Base Colour: MC1R Need two copies of to remove black & = normal ASIP = no black pigment

25 & Combinations

26 & Combinations Chestnut Bay

27 & Combinations In alpacas: More yellow pigment = More intense colour Darker ee alpacas will have dark skin And it will be hard to tell if it s black or dark mahogany Some animals with pink skin (genetically) will develop black pigment as they age

28 & Combinations The more black present, the greater the effect of ee White and fawn contains only negligible traces of black, so the only effect of ee is on the skin Bay plus ee becomes chestnut Black-bay plus ee can be anything from chestnut to fawn Black plus ee becomes chestnut through to white

29 DNA Identity There are three versions of MC1R that are & therefore prevent black pigment

30 Patterns Patterns are caused by genes that make a variation to the base colour All of the pattern genes have a wild-type allele that does nothing, plus one or more alleles that cause the pattern Every alpaca has two copies of each pattern gene, this could be: Two wild-type (do nothing) alleles One each of a wild-type and pattern-causing allele Two pattern-causing alleles

31 Grey Silvergrey and rosegrey are the result of the same pattern allele acting on different base colours Pale neck and legs, body diluted

32 Classic Grey Silvergrey is a classic grey allele on a black (or B&T) base colour Rosegrey is a classic grey allele on any other base colour

33 Classic Grey Some classic greys have spots or patches of undiluted fibre in random places Very hard to see on a pale background, and impossible to see on white One copy of the classic grey variant is required to cause the pattern An incomplete dominant Two copies of classic grey* is lethal at the embryo stage of development

34 Classic Grey: Evidence AAA herd books (E. Paul) Homozygous lethal, grey plus white spot involved with BEW ET (anecdotal) Grey x grey ET has lower stick rate Linkage mapping (F. Jackling, B. Appleton) BEW linked to two different markers Both markers located in/ near KIT gene

35 Classic Grey: Evidence Prospective mating records Grey x solid & grey x grey mating outcomes Parent Colours no grey 1 grey 2 grey Obs grey Obs non-grey Parent Colours no grey 1 grey 2 grey Obs grey Obs non-grey Exp grey Exp non-grey Exp grey Exp non-grey p=1.0 p= p=0.024 p=1.0 p= p=0.3052

36 Transcriptome data (R. Cransberg) Three variants between 10 silvergrey

37 KIT W5 W10

38 KIT W13 W17

39 KIT W18 W20

40 KIT plus MITF

41 White Spotting (Tuxedo/Piebald) May be caused by different genes, or by different alleles of the same gene KIT? MITF? PAX3? How the extent of the white is controlled is not known Genetic? Random?

42 White Spotting (Tuxedo/Piebald) Dominant or incomplete dominant One copy of the variant will cause the pattern Not known if two copies gives more white or not White will hide white-spotting If white x solid colour = white spotting; then the white parent is also white spotted But, even a tiny amount of white on a solid animal is an indication that it is actually white spotted

43 White Spotting (MITF & PAX3) Phenotypes of splashed white horses from a Quarter Horse family

44 White Spotting (MITF & PAX3) Phenotypes of horses with different Curtin University is a trademark of Curtin University Technology combinations of splashed white alleles

45 White Spotting (MITF) Macchiato coat colour phenotype

46 Roan Roan animals have a diluted body with undiluted head and legs Will get paler with age, and the body may end up almost completely white/silver Not always born with the pattern showing

47 Roan Roan can occur with any base colour Many white and fawn roans are not recognised as roan Roan is dominant or incomplete dominant Only one roan variant is needed to cause the pattern Homozygous roan =???

48 Roan (KIT) oads/1/6/5/1/ / png?340

49 Greying Age-related greying occurs in most species Caused by the premature death of stem-cells in hair follicles Unclear whether this kind of greying is a separate pattern in alpacas Could be a third variant of the roan pattern The physical attributes are similar to roan, except; no differentiation of effect between the body and legs not as intense effect The inheritance pattern is unknown in alpacas Extreme greying in horses is dominant

50 Appaloosa Appaloosa is a dark background with pale patches Can occur on top of any base colour The pattern of inheritance has not been proven, but is probably dominant or incomplete dominant Appaloosa can t be seen on white In horses, need both Lp/- plus Patn/-

51 Appaloosa

52 Vicuna

53 Blue Black vs. Warm Black Not caused by the currently known black variants in the Agouti gene Could be: Fibre structure Density of melanin Ratio of yellow to black melanin Environmental/ nutritional Behavioural Lack of cria tipping could be an indicator

54 Cria tipping vs. Delayed Expression Not caused by the currently known black variants in the Agouti gene Could be: Fibre structure Density of melanin Environmental/ nutritional Behavioural Cria tipping could be a sign

55 Acknowledgements & Thanks Funding by RIRDC, AAA, Curtin University and The Alpaca Research Foundation Natasha Feeley and Rhys Cransberg, contributed significantly to this work as part of their PhD studies All the alpaca breeders who have patiently answered questions about their animals, provided pedigrees, and donated samples