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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