Transcript AG-ASB-02.421-11.3P Animal_Science_Genetics

Genetics
Original Power Point Created by Casey Osksa
Modified by Georgia Agricultural Education Curriculum Office
June 2002
August 2008
What is Selection?
• Mating animals to produce certain
characteristics
• Low Birthweight
• Heavier Weaning Weight
• Color
• Horned or Polled
• Temperment
August 2008
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
August 2008
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
August 2008
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)
August 2008
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
August 2008
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?
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Punnet Square
P
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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?
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Punnet Square
P
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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
August 2008
Punnet Square: What sex will
the offspring be?
X
X
X X
X
X X
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Y
X Y
X Y
If Dad is bald, will you be
bald? Y
X
B
X
X
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XX
XX
B
B
X Y
XY
Baldness is carried by the
mother
X
X B
X
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X X B
X X
Y
X BY
X Y
What if Mom is bald?
X
X B
X B
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X X B
X X B
Y
X BY
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
August 2008
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?
August 2008
Shorthorn: Red X White
R
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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?
August 2008
Shorthorn: Red X Roan
R
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R
R
R
R
R
R
W
R
W
R
W
What if Both Parents are Roan?
R
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W
R
R
R
R
W
R
W
W
W
W
Undesirable Characteristics
•
•
•
•
Dwarfism
Monorchid = only one testicle descends
Cryptorchid = no testicles descend
Short ears & tails
August 2008
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
August 2008
What is an Abnormality?
• Similar to a Mutation, only it is caused by
something in the environment
• Siamese twins
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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
August 2008
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?
August 2008
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
August 2008
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
August 2008
What is Hybrid 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
August 2008
What are Exotics?
• Animals not common to United States
• Difficult to define today
• New breeds are exotics
August 2008
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)
August 2008