Lecture 12- Genetics (including coat color) Chapter 10 Gene – basic unit of inheritance. Genes are carried on chromosomes. Alleles – are the different forms of the same gene located at the same position on the chromosome. E,e E=black e=red Genes of somatic cells are always in pairs. Chromosomes are in the nucleus of all cells Genes are composed of DNA. ◦ The 4 Nitrogen bases are: Adenine (A) and thymine (T) Guanine (G) and cytosine (C) Genome – the complete set of genes for that organism. 64 chromosomes, 32 pairs. (31 somatic and 1 sex) Sex determination – XY in stallions, XX in mares. Sexed semen Alleles – two forms of the gene. ◦ Homozygous (GG, gg) ◦ Heterozygous (Gg) Dominant allele – expressed (G) Recessive allele – unexpressed (g) Genotype – genetic information Phenotype – How the expression of the gene appears ◦ Phenotype = genotype + environmental effects W – white gene obscures action of other genes WW is lethal Ww allele pair White lacks pigment in skin and hair ◦ Skin - pink ◦ Hair - white All non-white horses are ww. G – gray Dominant G ◦ GG or Gg will result in a gray horse. G allele horse can be born any color but gray but will gray out with age. Pigmented skin and eyes. At least one parent must be gray. All non-gray horses are gg. E – black gene EE or Ee is a black horse or at least has black points. ee is a red horse, liver chestnut, dark chestnut, chestnut, sorrel. A – Agouti; distribution of black hair AA, Aa gives black points if E is present aa presents a totally black horse if E is present C – pigment dilution CC : fully pigmented horses CCcr : red is diluted to yellow; black is unaffected. CcrCcr : red and black diluted to cream. Skin and eyes color diluted. Genetic contribution Genetic contribution from stallion: from mare: 50% chance of either allele in the sperm 50% chance of either allele in the egg C+ CCr 25% chance: C+C+ 25% chance: C+CCr C+ chestnut palomino 25% chance: C+CCr 25% chance: CCrCCr CCr palomino cremello D – dilutes both red and black pigment on the body but not on points. ◦ Dark points ◦ Dorsal stripe ◦ Shoulder stripe ◦ Leg barring ◦ Body is not diluted to cream. TO – white spotted patterns ◦ Tobiano is dominant ◦ Extends over shoulder ◦ Legs white ◦ Head dark TO,TO – spots TO,to – spots to,to – no spots Single Dilute Double Dilute No Dilution (nn) (nCr) (CrCr) Chestnut or Palomino Cremello Sorrel Bay Buckskin Perlino Black Smoky Black Smoky Cream https://www.animalgenetics.us/Equine/Cost_Dollar.asp http://www.animalgenetics.us/Equine/CCalculator1.asp Equine Genome published in 2007 In humans, certain genes have been associated with athletic performance ◦ Possible similarities in horses? ◦ Vet J, 190:39-48, 2011 http://www.horsejournals.com/horse-genome-revealed The nucleotide at one part of the myostatin gene seems to be associated with “speed” in Thoroughbreds ◦ C nucleotide: speed ◦ T nucleotide: stamina Remember: horses have 2 sets of chromosomes and each one will have a copy of the myostatin gene ◦ C/C: sprint performance (less than 1 mile) ◦ C/T: middle distance (~1-1.5 miles) ◦ T/T: longer distance (> 1.25 miles) Important to note that speed is controlled by much more than just 1 gene http://www.equinome.com/pages/the-equinome- speed-gene-test.html Mule = mare + jack Hinny = jenny + stallion Horses: 64 chromosomes Donkeys: 62 chromosomes Results in sterile offspring Mules and Hinnies: 63 chromosomes Male donkey + horse mare = mule horse stallion + female donkey = hinny Zorse = zebra stallion + horse mare ◦ AKA zebrula, zebrule, or zebra mule ◦ The rarer reverse pairing (female zebra + male horse) is sometimes called a horbra, hebra, zebrinny or zebret ◦ Sterile Zony = zebra stallion + pony mare ◦ Medium-sized pony mares preferred if riding ◦ Zetlands Zebra-donkey ◦ zonkey, zebonkey, zebronkey, zebrinny, zebrula, zebrass, zedonk, and zebadonk, zebra hinny, donkra .