Introduction to Genetics and Coat Color Genetics

1. Introduction to Geneticsand Coat Color Genetics Dr. N. Matthew Ellinwood, D.V.M., Ph.D. March 12-24, 2014 Iowa State University College of Agriculture and Life Sciences

2. Goals: • Review of genetic terminology • Genotypes and phenotypes for coat colors in various breeds of dogs • Epistasis • Primary known genes controlling coat color and color patterns • Understand the basis of coat color at the genetic and biochemical level

3. Terminology • Chromosomes • Haploid • Diploid • Meiosis • Genes • Locus • Genotype • Phenotype • Traits • Epistasis

4. Chromosomes • DNA and associated proteins • Acrosomic • 78 chromosomes in domestic dog • Autosomal • 38 pairs • Sex chromosomes • 1 pair (XX or XY) • Gametes

7. Haploid vs. Diploid • Somatic cells are diploid • Two sets of chromosomes • One maternal, one paternal • Mature germ cells are haploid • Meiosis • Meiosis: genetic recombination of parental chromosomes • Crossovers http://publications.nigms.nih.gov/insidethecell/chapter4.html

8. http://www.carisgamba.com/CTmeiosis/meiosis-big.gif Meiosis • Two divisions • First division like mitosis • Second division yields haploid cells - Gametes

9. Crossing Over Process which occurs during the early stages of cell division in meiosis. Homologous chromosomes may exchange segments of DNA. This produces genetic variations in germ cells.

10. Genes and Loci • Essentially the same thing • Locus (plural: loci) • An older term pre-dating the DNA and gene sequence age • Example • E locus (extension) • MC1r gene (melanocortin 1 receptor) • Genotype versus phenotype

11. E E E e e e Genotype versus Phenotype • Genotype: the combination of alleles • Two copies per loci • Three possibilities for a bi-allelic gene • EE (homozygous dominant) • MC1R +/+ • C916, C916 • Ee (heterozygous) • MCIR +/- • C916, C916T • ee (homozygous recessive) • MC1R -/- • C916T, C916T • Phenotype: the physical expression of the genotype in combination with environmental factors

12. (Example of Complete Dominance) EE Ee ee http://farm1.static.flickr.com/186/480102965_6329aede20.jpg

13. Traits and Inheritance • Traits • Qualitative versus quantitative • Sex limited versus sex linked • Simple gene action and inheritance • Dominant/recessive – A/a • Three genotypes, two phenotypes • Incomplete dominance • Three genotypes, three phenotypes

14. Traits and Inheritance (Con’t) • Complex gene action and inheritance • Polygenic versus monogenic/digenic • Polygenic: more than one/two genes involved • Interactions between genes • Additive, epistasis, modifier

15. ee ee ee Modifier Genes in Golden Retrievers

16. Example of Additivity • Four alleles for spotting may act additively to produce gradations of spotting.

17. Epistasis • Suppression of the effect of a gene by a non-allelic gene • A gene located at one locus “hides” the action of another gene at a different locus • Can occur on the same chromosome or differing chromosomes • Sometimes simply referring to an interaction • Example: • Dominant black at the K locus is “dominant” over certain alleles at other loci

18. Coat Color Genetics • Basis of Color • Coat color loci • Inheritance • Functionality • Genotypes • Associated phenotypes

19. http://en.wikipedia.org/wiki/Image:Illu_skin02.jpg Biochemical Basis of Color • Melanin – produced by melanocytes • Tyrosinine • Enzymatically alltered • Eumelanin • Dark – black or brown • Phaeomelanin • Light – cream, tan, or red

20. Cellular Basis of Color • Neural Crest Cells • Derived at the border of the developing “Neural Tube” and Epidermis • Migrate throughout the body to give rise to many tissues • Including melanocytes • Melanocytes possess special organelles • Melanosome • Site of pigment production http://wikis.lib.ncsu.edu/index.php/Group_4_COURTNEY_BOYD_,_MEREDITH_CRAVER_,_ERIC_LAND http://www.nature.com/nrm/journal/v9/n7/box/nrm2428_BX2.html

21. Coat Color Phenotype • The physiology of color phenotype is a complex integration of: • Melanocyte survival and migration • Enzymatic and other intracellular components involved in • Pigment production • Pigment deposition in melanosomes/hair shafts • Endocrine/seasonal signaling involving pigment production

22. Coat Color Genetics in Dogs A – Agouti E – Extension K – Black B – Brown M – Merle D – Dilution (Blue) G – Graying R – Roaning T – Ticking S – White spotting • Primary, recognized genes controlling coat color:

23. http://ib.berkeley.edu/courses/ib162/Week3a_files/image001.gifhttp://ib.berkeley.edu/courses/ib162/Week3a_files/image001.gif Agouti Color • Versus the Agouti Locus • Basic color of many wild animals • Camouflage • Patterns on individual hairs and over the body • Stripes or banding on individual hairs • Dark: often near hair tips • Pattern over the body

24. http://consejo.bz/belize/images/animals/herbivores/agouti.jpghttp://consejo.bz/belize/images/animals/herbivores/agouti.jpg Agouti – Agouti Color

25. Agouti Locus • Function of agouti • Inhibits signaling through MC1r • Receptor antagonist • Shuts off eumelanin production • Default phaeomelanin production • Expression specific to: • Hair growth cycle • Body position

26. KK Ee _ _ ee kk atat http://hometown.aol.com/felderhavenrotts/images/marlos%20kassianna%20v%20rome%20sitting%20low%20res.jpg http://farm1.static.flickr.com/186/480102965_6329aede20.jpg Eumelanin versus PheomelaninRecessive black due to inactivation of agouti signaling peptide gene (aa), constitutive activation of MC1r by the black allele at K (beta-defensin), inactivation of MC1r (ee), and agouti signaling peptide antagonism of MC1r (atat) aa

27. Agouti Locus in Dogs

28. Airedale - asa asa Rottweiler - at at F1 cross = asa at Agouti Locus in Dogs

29. K (Dominant) Black Locus in Dogs • Dominant allele epistatic to alleles at agouti Alleles for dominant black locus Description Symbol Dominant black K Brindle kbr Normal k

30. Brindle Great Danekbr_ Black LabradorKK http://www.doglogic.com/brindleroka.jpg http://farm1.static.flickr.com/186/480102965_6329aede20.jpg K Locus in Dogs

31. Brindle Coat Color in Dogs • Several theories were proposed • E locus as Ebr • Tabby (Ta) as in cats • K, kbr, k • Experimental evidence in greyhounds corroborates the existence of a separate locus (K) • b-defensin: Previously unknown to be involved in pigment • Binds MC1r • Agonist activity of MC1r

32. Greyhoundkbr_ Great Danekbr_ http://puppydogweb.com/gallery/greyhounds/greyhound_paulsen.jpg http://homepage.usask.ca/~schmutz/Dane Brindle Coat Color in Dogs

33. Extension Locus in Dogs • Epistatic to A and K loci (depending on the alleles at E) • Historically great disagreement over alleles for E locus • Early work lists three or four • Early work does not agree with results in other mammals • Recent molecular work seems to indicates EM, E, and e • EMEM, or EM_ • Black Mask, Exception: hypostasis to K (K_) and A (aa) • EE, or E_ • Normal MC1r function, normal A locus expression • Exception: hypostasis to K (K_) • This is as it were by allowed expression of the agouti locus …. • ee • Entire agouti series is hypostatic to ee at the E Locus • Ay, AW, asa, at, a result in red/yellow

34. BraccoItalianobbE_ Irish SetterB_ee http://www.dkimages.com/discover/previews/798/75005078.JPG http://www.dkimages.com/discover/previews/818/594875.JPG Extension Locus in Dogs

35. Brown Locus in Dogs • Brown locus in dogs - B, b • Tyrosinase related protein 1 (TRP1) • Eumelanin pigment granules in melanosomes in bb dogs are smaller and more round • Influences the perceived color • Little to no effect on phaeomelanin • B_ dogs are black • bb dogs are liver or chocolate colored • Have brown nose leather

36. Chocolate Labradorbb Black LabradorB _ http://www.pointinglabtx.com/Pedigrees.htm http://farm1.static.flickr.com/186/480102965_6329aede20.jpg Brown Locus in Dogs

37. Dilution Locus in Dogs • Influences dispersion of pigment granules • Eumelanin and phaeomelanin • Now known to be melanophilin

38. WeimaranerB_ddKK http://www.weimaranerowner.com/portals/54/weimaraner-blue-hair.jpg Dilution Locus in Dogs WeimaranerbbddKK

39. Miniature Pinscher atatB_D_kk atatbbddkk Dilution Locus in Dogs

40. Graying Locus in Dogs • Not well understood • Animals are born with normal color and lighten with age - prematurely • Believed to be present in: • Poodles • Old English Sheepdogs • Terriers • Incomplete dominance - additivity? • GG - extreme lightening • Gg - slight lightening

41. Graying Locus in Dogs Kerry Blue TerrierK_G_

42. Merle Locus in Dogs • Incomplete dominance • Causes patchy dilutions in coat and eye colors • Mutation in silver gene (SILV) • Additive gene • Normal dogs - mm • Homozygous MM dogs often have abnormalities: • Deafness • Blindness • Small eyes • Strongly recommended to avoid mating two merles

43. Merle Locus in Dogs Cardigan Welsh Corgiasa asa Mm

44. Other Conditions • Not characterized at the molecular level • Complex beyond the scope of this class

45. Harlequin Locus in Dogs • Predominately white with black “torn” patches • A dually heterozygous state • Harlequin (Hh) and merle (Mm) • Homozygous HH • Not compatible with life • Does not breed true • Only observed in Great Danes • Genetics now known at molecular level

46. Great DaneD_K_HhMm http://www.all-about-great-danes.com/images/harlequin.jpg http://www.kennels.co.uk/images/RavendaneHarlequin.jpg Harlequin Locus in Dogs

47. Spotting Locus in Dogs • Percent white probably influenced greatly by modifier genes • Molecular genetics still incompletely understood

48. Spotting Locus in Dogs (Con’t) • S – solid color, no white • si – Irish allele (from Irish rat), few definitely spotted areas • sp– piebald 15-20% of coat solid (pigmented) • sw – extreme piebald, virtually no spotting • i.e. solid white

49. Spotting Locus in Dogs • S = 0 • si = 1-3 • sp = 3-9 • sw = 9-10

50. Ticking Locus in Dogs • White areas have flecks of color • Most dogs are tt