GeneticsGenetics

What is What is GeneticsGenetics??• 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 What are Dominant Dominant GenesGenes??

• Dominant Genes = one gene overshadows the other

• Angus Cattle: black is dominant, red is not (Bb)

• Hereford: white face is dominant (Ww)

• Hampshire Hog: white belt is dominant

• Horns are dominant (Pp)

What are What are Recessive Recessive GenesGenes??

• 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 SquarePunnet Square• P = horned• p = polled• If a homozygous horned cow

(PP) is mated to a homozygous polled bull (pp), what percent of the calves will be horned, polled?

Punnet SquarePunnet SquareP Ppp

Pp PpPp Pp

Punnet SquarePunnet Square• If a homozygous horned cow

(PP) is mated to a heterozygous horned bull (Pp), what percent of the calves will be polled?

Punnet SquarePunnet SquareP Ppp

Pp PpPp Pp

What are What are Sex Linked Sex Linked GenesGenes??

• 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

What is What is Incomplete Incomplete DominanceDominance??

• If both genes express themselves

• Shorthorn Cattle: Red male mated to a White female = Roan calf

• RR + WW = RW

Punnet SquarePunnet 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 WhiteShorthorn: Red X WhiteR RWW

RW RWRW RW

Punnet SquarePunnet Square• If a red bull (RR) is mated to a

roan (RW) cow, what color will the calves be?

Shorthorn: Red X RoanShorthorn: Red X RoanR RRW

RR RRRW RW

What if Both Parents are What if Both Parents are Roan?Roan?R W

RW

RR RWRW WW

What is a What is a MutationMutation??• 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?What is an Abnormality?• Similar to a Mutation, only it is

caused by something in the environment

• Siamese twins

What is Heritability?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

HeritabilityHeritability• 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?

HeritabilityHeritability• What is the difference in current

weaning wt and that of the new ram?110 - 70 = 40 lbs

• Heritability % x difference30% x 40 = 12 lbs

• Can expect a gain in weaning wt of 12 lbs

• 70 lbs + 12 lbs = 82 lbs

What is What is Hybrid VigorHybrid Vigor??• Offspring will outperform either of the parents

• 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

Genetic TermsGenetic Terms• Genotype: genetic makeup (Bb)• Phenotype: physical appearance

(Black)• Heterozygous: Genes are

different, Dominant & Recessive (Bb)

• Homozygous: both genes are the same (BB or bb)