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Genetics Genetics Terms • Heterozygous = two different types of genes (Bb) • Homozygous = two similar genes (BB) • Dominant Gene = trait overpowers others • Recessive Gene = must be accompanied with another recessive gene to express trait • Incomplete Dominance = both traits express themselves Genetic Terms •Genotype - genetic makeup (Bb) •Phenotype - physical appearance (Black) •Heterosis - Genes are different, Dominant & Recessive (Bb) What is Selection? •Mating animals to produce certain characteristics •Low Birth Weight •Heavier Weaning Weight •Color •Horned or Polled •Temperment What makes an animal the way it is? •Animals are result of Feed, Health, and Inheritance (genetic material) •Feed is fastest to correct •Genetics last longest What are Genetics? • All body cells contain “Blueprints” with instructions as to how an animal will look or act, etc. • One Gene comes from each parent (pairs) • Genes are divided into sections (Chromosomes) that carry genes • Sex chromosomes: – male = XY, – female = XX What are Dominant Genes? • Dominant Genes are traits that overpower other types of genes • Angus Cattle: black(B) color dominant, red (b) color recessive (Bb) • Hereford: white (W) face cattle dominant over colored (w) recessive (Ww) • Hampshire Hog: white (W) belt dominant, color (w) recessive (Ww) • Polled (P) cattle are dominant over horned (p) recessive (Pp) • Black (B) horses dominate, brown (b) recessive (Bb) What are Recessive Genes? •The gene that is overshadowed by a dominant gene •Recessive genes can only express themselves if both genes are recessive •Polled vs Horned (Pp) (pp) •Black wool vs white (Ww) (ww) •Dwarfism vs normal size (dd) •Albino Punnet Square •P = polled •p = horned •If a homozygous polled cow (PP) is mated to a homozygous horned bull (pp), what percent of the calves will be horned, polled? Punnet Square p p P Pp Pp P Pp Pp Punnet Square •If a homozygous polled cow (PP) is mated to a heterozygous horned bull (Pp), what percent of the calves will be polled? Punnet Square P P PP p Pp P PP Pp What are Sex Linked Genes? • Some recessive genes are attached to the X and Y chromosomes • Humans: Colorblindness and Baldness are on the X chromosomes • In Men, traits expressed anytime present • In Women, must have two recessives to show trait • Children get baldness from mothers Punnet Square: What sex will the offspring be? X X XX X XX Y XY XY If dad is bald, will you be bald? XB Y X X XB XY X X XB XY Baldness is carried by the mother X Y XB X XB XBY X XX XY What if mom is bald? X Y XB X XB XBY XB X XB XBY What is Incomplete Dominance? •If both genes express themselves •Shorthorn Cattle: Red male mated to a White female = Roan calf •RR + WW = RW Punnet Square •Shorthorn Cattle •R = Red •W = white •RW = roan •If a red bull (RR) is mated to a white cow (WW), what color will the calves be? Shorthorn: Red X White R R W RW RW W RW RW Punnet Square •If a red bull (RR) is mated to a roan (RW) cow, what color will the calves be? Shorthorn: Red X Roan R R RR R RR W RW RW What if Both Parents are Roan? R R RR W RW W RW WW Undesirable Characteristics •Dwarfism •Monorchid = only one testicle descends •Cryptorchid = no testicles descend •Short ears & tails What is a Mutation? • Dramatically different from what is expected genetically • Horned calf from polled parents • Loss of some or extra body parts • Lethal Mutation: causes death at birth • Sublethal Mutation: limits animals ability to grow to maturity • Beneficial Mutation: loss of tail in lambs What is an Abnormality? •Similar to a Mutation, only it is caused by something in the environment •Siamese twins What is Heritability? •Chance that traits will be inherited •Low: multiple births, fat covering •Medium: birth wt, wean wt, milk, wool grade, carcass wt, rate of gain •High: Loin eye area, fleece length & quality Heritability • Currently have ewes that wean 70 lb lambs • Want to raise weaning wt to 110 lbs • Select a ram with a wean wt of 110 lbs • Heritability of weaning wt is 30% • What can you expect new lamb crop to weigh at weaning? Heritability •What is the difference in current weaning wt and that of the new ram? 110 - 70 = 40 lbs •Heritability % x difference 30% x 40 = 12 lbs •Can expect a gain in weaning wt of 12 lbs •70 lbs + 12 lbs = 82 lbs Mating Systems • Random Mating: all males have an equal opportunity to mate with all females • Outcrossing: mating purebreds with unrelated purebreds • Inbreeding: mating related animals – Linebreeding: parents mated to offspring • Crossbreeding: mating animals of same species but different breeds Crossbreeding •mating of animals of different breeds •can increase productivity •produce animals with combination of traits •foundation stock for new breeds •introduce new genes quicker than in purebreds What is Hybrid Vigor? • Offspring will out-perform either of the parents, also know as heterosis. • Corn Breed A yields 100 bu/acre • Corn Breed B yields 100 bu/acre • Crossbreed A & B yields corn that yields 200 bu/acre • Vigor only expressed in crossbreeding • Donkey mated to a horse = Mule – mule is sterile What are Exotics? •Animals not common to United States •Difficult to define today •New breeds are exotics