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					Genetics

What is Selection?
• Mating animals to produce certain characteristics • Low Birthweight • Heavier Weaning Weight • Color • Horned or Polled • Temperment

What makes an animal they way that they are?
• Animals are the result of Feed, Health, and Inheritance (genetic material) • Feed is fastest to correct • Genetics last longest

What is 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 = 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 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 = 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 Square
P P

p

P

p

P

p

p

P

p

P

p

Punnet Square
• If a homozygous horned cow (PP) is mated to a heterozygous horned bull (Pp), what percent of the calves will be polled?

Punnet Square
P P

p

P

p

P

p

p

P

p

P

p

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 Y

X

X X

X Y

X

X X

X Y

If Dad is bald, will you be bald?
X B Y

X

X X B

X

Y

X

X X B

X Y

Baldness is carried by the mother
X Y

X B

X X B

XBY

X

X X

X Y

What is Mom is bald?
X Y

X B

X X B

XBY

X B

X X B

XB Y

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

R

W

R

W

W

R

W

R

W

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

R

R

R

R

W

R

W

R

W

What if Both Parents are Roan?
R W

R

R

R

R

W

W

R

W

W

W

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

• 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

What is Hybrid Vigor?

What are Exotics?
• Animals not common to United States • Difficult to define today • New breeds are exotics

Genetic Terms
• Genotype: genetic makeup (Bb) • Phenotype: physical appearance (Black) • Heterosis: Genes are different, Dominant & Recessive (Bb) • Homozygous: both genes are the same (BB or bb)


				
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Laura Trunk Laura Trunk
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