By Meranda Small Extension Educator Heredity The science that studies how animals inherit characteristics or traits from parents and pass these traits to offspring Genetics terminology Chromosome carriers of the basic units of heredity ID: 999170
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1. Will my calf have horns or not?! – geneticsBy: Meranda Small, Extension Educator
2. HeredityThe science that studies how animals inherit characteristics or traits from parents and pass these traits to offspringGenetics
3. terminologyChromosome: carriers of the basic units of heredityGene: basic unit of heredity that is located on chromosomes and affects a specific traitGenotype: genetic make-up of the animal
4. TerminologyHeritability: amount of variation in a trait resulting from genetic differencesHeterosis: increase in performance associated with the crossbred animal when compared to the average of the purebred parentsHeterozygous: gene pair with different genes for the same trait (pp)
5. TerminologyHomozygous: gene pair where both genes are identical (PP)Phenotype: expression of genetic traits (physical)Prepotency: ability of an animal to make its offspring resemble it and each other more closely than usual
6. TerminologyTrait: an animal characteristic that can be selected forQualitative traits: traits that are controlled by only one gene pairQuantitative traits: traits that are controlled by multiple gene pairs and influenced by environmental factors
7. Dominant vs. Recessive genesParents each donate one gene to the offspring, giving it a pair. Genes can be either dominant or recessive. The ability of some genes to mask or cover up the presence of other genes is called DOMINANCE. The gene that is masked is called RECESSIVE (p), and the gene that has the ability to mask the recessive gene is called DOMINANT (P)
8. Traits of economic importanceSheepReproduction – these are traits, such as lambs weaned per ewe and out of season breeding, which are lowly heritable. But, these are still important in economical sheep productionGrowth – this is a moderately heritable trait that can be selected for with good response. Examples of this are birth weight and weaning weight
9. Traits of economic importanceSheepCarcass Merit – Carcass traits are fat thickness or loin eye area. These traits are moderately to highly heritableConformation – this refers to the structural make up of the animal and is moderately to highly heritableWool – wool characteristics like fleece weight and grade are highly heritable
10. Traits of economic importanceBeefReproductive performance – includes fertility level, calving ease, and maternal abilityFertility level – level in bulls determined by breeding soundness exam *Research indicates bulls with larger scrotal circumference have increased fertility and daughters of such bulls reach puberty at younger age
11. Traits of economic importanceBeefReproductive performanceCalving ease – influence by birth weight, should be highly considered when evaluative dam and sire pairing. Select for a low birth weight sire to use on heifersMaternal ability – milk production, reflected by calves weight at weaning. Select sires that excel in this trait as milk production is passed to daughters. Match this trait with the environment
12. Traits of economic importanceBeefGrowth rate and feed efficiency – measured using adjusted 205-day weaning weights, postweaning gain, and adjusted 365-day(yearling) weights (best selection trait). Selecting for growth (daily gain), can indirectly select for feed efficiency
13. Traits of economic importanceBeefConformation traits – include structural soundness and natural muscling. A structurally sound beef animal is one that has a lengthy, productive life in the herd.Carcass traits – proportion of fat to lean (yield grade)Yield grade is determined by carcass weight, external fat cover, rib eye area, and % pelvic/kidney/heart fatQuality grade is determined by maturity and marbling score (indicates eating quality for juiciness, marbling, tenderness, flavor)
14. Traits of economic importanceSwineReproduction – semen quality, farrowing rate, litter size, non-productive sow days, longevityGrowth – days to market, feed conversion, mortalityCarcass/meat - % Lean, eating quality (marbling, color, pH)
15. HeritabilitiesBeef Swine
16. HeritabilitiesSheepReproductivePercentFleecePercentEwe fertility5Grease fleece wt.35Lambs born per lambing10Clean fleece wt.25SC35Yield (%)40Age at puberty25Staple length55Lamb survival5Fiber diameter40Lbs. of lamb weaned/ewe exposed20Crimp45Color45
17. HeritabilitiesSheepGrowthPercentCarcassPercentBW15CW3560-day weight20Weight of trimmed retail cuts4590-day weight25% trimmed retail cuts40120-day weight30LEA35240-day weight4012th rib fat thickness30Preweaning gain20Dressing %10Postweaning gain40
18. Inherited defectsSheepColor – undesired spots/dark patches in woolCryptorchidism – one or both testes of the ram may be retained in the abdomen. Greatly reduces fertility. Also occurs in Beef and SwineDwarfism – very serious defect that results in abnormally short legs, decreased fertility and short life spanEntropion (inverted eyelids) – lower eyelid rolls in, causing eye irritation
19. Inherited defectsSheepFace covering – too much wool on face causes problems with vision and reduces productionFleece defects – imperfections such as high belly wool, hairiness, and fuzzies should be avoided as they reduce valueHorns & scurs – defect in polled breedsJaw defects – undershot/overshot jaws where teeth don’t meet the pad
20. Inherited defectsSheepRectal prolapse – weakness that causes the sheep to push out part of the rectal tissueSkin folds – wrinkles make sheep hard to shearSpider lamb syndrome – recessive trait that results in lambs with deformed legs and spines. These lambs die early and rarely reproduce. Very serious defect that is currently appearing in some breeds of sheep
21. Inherited defectsSwinePorcine Stress Syndrome (PSS) – “stress gene” causing susceptibility to external stress associated with movement, mixing, changes in environment. Stress positive pigs produce Pale, Soft and Exudative (PSE) carcasses. Associated with the Pietrain breedRendement Napole Gene – causes pigs to have undesirable muscle quality attributes. Associated with poor firmness/wetness scores, excessive moisture loss and poor processing. Has been associated in the Hampshire breed
22. Inherited defectsSwineScrotal Hernia – results from a weakness of the muscles that surround the inguinal canal, permitting the intestine to drop into the scrotumAtresia Ani – condition characterized by a pig being born without rectal opening. Boar pigs die without surgical interference while females can defecate through the vulva and grow normallyHermaphrodites – pigs that carry both male and female sex organs
23. Inherited defectsSwineOther genetic abnormalities – rectal prolapse, hair whorls, screw tail, blood warts, brain hernias, cleft palate, gastric ulcers, bleeders, humpback, hydrocephalus, leukemia, splay legs, tremors, extra toes, mule foot
24. Inherited defectsBeefDwarfism – three forms (snorter, bulldog, long-headed). Has been found in Hereford, Angus, Brahmans, and DextersOsteopetrosis (marble bone) – calves aborted early, calves born have short lower jaw, bones contain no marrow cavity and are fragile. Has been found in Red AngusIdiopathic Epilepsy – calves have stressed induced seizures. Found in horned Herefords
25. Inherited DefectsBeefTibial Hemimelia – calves born dead or die soon after birth with twisted legs, fused joints, hernias, and holes in the skull. Seen in Shorthorns and crosses into “show steers”Pulmonary Hypoplasia with Anasarca – calves born dead or die shortly after birth. Calves have water-logged appearance, small lungs and no lymph glands as fetus begins to accumulate fluid by 6th month of gestationProtoporphyria – calves sensitive to light and develop hair loss, sores and fail to thrive. Previously found in Limousin cattle but greatly removed
26. Inherited defectsBeefBeta-Mannosidosis – calves exhibit weakness, incoordination, head-swaying, poor suckling reflex, nervous system disorders. Previously found in Salers but has been practically eliminatedArthrogryposis Multiplex (curly calf syndrome) – calves born dead or die shortly after birth, small in size with diminished muscling, fixed joints, twisted limbs and spine. Found in AngusNeuropathic Hydrocephalus – calves born dead, full term, weighing 25-35lbs. with a basketball sized head full of fluid and no brain. Found in Angus
27. Inherited defectsBeefHypotrichosis – hairlessness, with some calves being practically slick. Others have extremely curly hair. Not lethal but calves often succumb to elements. Found polled Herefords, Charolais, Simmental, and dairy breedsFawn Calf Syndrome – subtle, non-lethal with calves appearing hunched or crouched, less extension of the upper limb joints. Has been found in Angus