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 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 P PP 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? Y X XX XY X XX XY

If dad is bald, will you be bald? X Y B X X X X Y B X X X XY B

Baldness is carried by the mother X Y X X X X Y B B B X X X X Y

What if mom is bald? X Y X X X X Y B B B X X X X Y B B B

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 RW RW W 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 R RR RR W RW RW

What if Both Parents are Roan? RR 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