Horse Science Equine Genetics Introduction n Not been

Horse Science Equine Genetics

Introduction n Not been utilized as efficiently in horses n Primarily for recreation n What are horses primarily selected for? n Conformation n Athletic ability n Intelligence

Introduction n In each horse there is a certain portion of characteristics that are due to: Genetics n Environment n n What is genetic influence? n Portion that is passed from parent to offspring

Genetics n Each body cell contains a complete copy of genetic material where? n Nucleus n This material is contained in: n Chromosomes n n Long, slender, thread-like structures that are paired How many do horse have? § 64 § Humans have 46

Genetics n What is the basic unit of inheritance? n The gene n n Located on chromosomes Each horse has 32 pairs § Half from sire and half from dam n Genes are located at various locations along the chromosomes n Loci

Genetics n Genes control the expression of traits n Correspond to chemical structures (messengers) that determine individual traits n As chromosomes are paired, so too are genes n Paired genes (alleles) may or may not be identical n If the paired genes are identical n Then the individual is considered to be homozygous n If not, heterozygous

Genetics n Two basic types of genetic action: n Qualitative n Quantitative n Qualitative: n n n Particular trait influenced by single pair of genes Or maybe 2 or 3 Quantitative: n Influenced by a number of genes

Genetics n Three primary types of gene action that affect qualitative gene action: n Dominance n Co-dominance n Partial Dominance

Dominance n One dominant gene is required to n Display a particular trait n Two recessive genes are required to n Display a recessive trait n Example: Combined Immune Deficiency § Two recessive traits being exhibited

Co-dominance n Results in an intermediate state n Between two parents n Example: blood type n Each blood type is different and known and thus indicates the genotype

Partial Dominance n Also results in an intermediate state but n Not necessarily an exact intermediate state n Ex: Dilution gene affecting color n When one dilution gene is present, the base color is altered to? n Buckskin or Palomino n Two are present? n Cremello or Perlino

Quantitative n Most traits in horses are influenced by quantitative gene action: Example? n What are some factors that might affect speed? n n n Size and length of leg Efficiency of heart, lungs, and legs Mental traits: desire and determination

Heredity vs. Environment n What factors are affected primarily by environment? n Nutrition, Training, Reproductive Ability n What factors are affected primarily by genetics? n Color n What factors are affected by both? n Mature Size, Longevity, Racing Speed

Heritability Estimate n All traits have an estimate n Defined as: n Percentage of horse’s expressed trait that is due to genetics n Indicates the probability of that trait being passed from one generation to the next n Some traits are highly heritable n Others are low

Heritability n Greater progress can be made when n Number of traits selected to a minimum n If a horse is selected for only one trait n Greater selection pressure can be applied on that trait n Selecting for traits that are highly heritable n Greatly increases chance for improvement

Color Coat Genetics n A horse’s color is a result of what? n Fairly complicated interactions of several independent events n Each horse has only one color, but n Many different white areas can be superimposed to change the final appearance n White actually, covers up the colored areas, rather than the opposite

Color Coat Genetics n Color traits are controlled by: n Genes that can interact in various ways n Genes occur in pairs n One from sire and one from dam n Dominant genes are ones that are expressed n Even when paired with an unlike gene n Recessive genes can only be expressed if what? n Both pairs are the same

Colors n What are three basic colors of horses? n Bay n Black n Sorrel/Chestnut n Also provide the basis for most other colors n Understanding the genetic control of these colors is: n Critical to understanding the rest of the colors

Colors n Sorrel is recessive to both black and bay n Sorrel ee n Bay Ee n Black EE n Bay and Black are controlled by a separate genetic locus than sorrel n Black (a) is recessive to Bay (A)

Colors n Bay n AAEE, Aa. EE, AAEe, and Aa. Ee n Black n aa. EE, aa. Ee n Sorrel n AAee, Aaee n The most important detail is that sorrel horses do carry either black or bay determining genes, but they are not expressed with the presence of ee

Colors n The sorrel masking is a strange result n Very common (Breed True) n Once interactions of bay, black, and sorrel are understood, we can move on to others n Cremello (incompletely dominant) n One dose lightens red areas to yellow leaving black areas unaffected n Two doses will lighten red and black to cream n One dose on black is smokey

Colors n Smokey color horses can also produce n Buckskin and Palomino foals n Bay to: n Buckskin n Sorrel to: n Palomino n Sorrel to: n Cremello n Bay to: n Perlino

Colors n Duns n Result of a single dominant gene Dn interacting with a basic color n Result on bay is: n n Black to: n n Zebra dun Grullo Sorrel to: n Red dun

Colors n Other variation of color are more rarely encountered than those previously mentioned n These variations probably not due to single genes n Included are: n Flaxen manes and tails n Dark overlays on some n n n Sorrels Bays Liver chestnuts

Colors n Silver Dapple Gene (Z), which is dominant n Rare in most breeds n Acts to make black areas pale n Leaves red areas unaffected n Somewhat opposite of Cremello n Black background to blue silver n Bay Background to red silver

Colors n Minor white marks on faces and legs n Controlled by multiple genes n Horses may add or subtract color to their offspring dependent upon n Genetic makeup

Color n Gray n Born dark or solid, progressively gets lighter with age n Due to white hairs that grow into coat n May be dapple n Have dark skin n Dominant gene GG or Gg n Each gray horse must have a gray parent

Color n Roan n White hairs mixed with base coat n Can be superimposed over any base color n Head, mane, tail, and lower legs are solid n Dominate gene Rn n All roan horses are heterozygous n Homozygotes die early in development

Color n Paint patterns n White spotting irregularly arranged over body n Tobiano most common To n n Usually have four white feet, white lower legs, little white on head, white across topline Overo Dominant O n n Most have dark feet and dark lower legs, white on face, blue eyes, not across topline Associated with lethal white foal syndrome

Colors n Leopard n All related to a single gene Lp n Incompletely dominant n Responsible for: n n n Mottled Varnish roan Blanket with spots Blanket Frost Leopard

Genetic Abnormalities n HYPP n Hyperkalemic Periodic Paralysis n Dominant Gene n Linked to QH Impressive n n n Defect in movement of Na and K in & out of muscle Attacks of muscle weakness Tremors Collapse Death

Mr. Conclusion

Genetic Abnormalities n Parrot Mouth and Cryptorchidism n Lethal White Foal Syndrome (OLWS) n Failure to form certain types of nerves in intestinal tract n Foals die of colic several days after birth n Affects some offspring produced by mating two overo paints

Genetic Abnormalities n Hereditary Equine Regional Dermal Asthenia n Aka HERDA n Linked to Poco Bueno Line n Collagen defect n Skin detaches

Poco Bueno