Post on 16-Apr-2017
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)