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B65 Animal Genetic
Lesson Outline
• Introduction
• Phenotype
• Environmental
Factors
• Natural Selection
• Controlled breeding
• Two-Breed Cross
• Three Breed
Rotation Cross
• Gene Transfer
• Genetic Engineering
• Differentiation
• Alleles
• Gene Dominance
• Punnett Square
• Mendilin Genetics
• Codominate Genes
• Additive Expression of
Genes
Introduction
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No two animals are exactly alike. Even with twins one may be
taller, one may be heavier, or grow faster.
The two main factors that contribute to these differences in
animals are:
The environment.
The genetic make up of the animal.
Infovets Educational Resources – www.infovets.com – Slide 3
Phenotype
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The phenotype is the physical appearance of the animal.
The genotype is the genetic make up of the animal
Both the environment and the genetic make up effect the physical
appearance of the animal.
Infovets Educational Resources – www.infovets.com – Slide 4
Environmental Factors
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The quantity and quality of the feed
Climate conditions
Exposure to parasites and diseases
The type of terrain (steep mountains, desserts, irrigated pasture)
The producer has a lot of control over the animal’s environment.
A producer can also influence, to a lesser degree, the genetic make
up of an animal.
Infovets Educational Resources – www.infovets.com – Slide 5
Natural Selection
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In nature, genetics are passed on through the process of natural
selection. The strongest, healthiest, most powerful animal
generally spreads its genetics. Animals that are weak may have a
poor immune system and are diseased, or may have conformation
problems. Generally these animals do not survive long enough to
pass on their genetics.
Infovets Educational Resources – www.infovets.com – Slide 6
Controlled Breeding
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A producer crosses two parents based on a desired outcome.
A tough, dominant, alpha male may not be a desirable trait for
domestic animals.
Agriculture producers select for traits that have economic
importance, such as low birth weight, growth rate, feed efficiency,
mothering ability, carcass traits.
The economically important traits are influenced by both the
environment and the genetic make up of the animal.
Infovets Educational Resources – www.infovets.com – Slide 7
Controlled Breeding Programs
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Outcrossing: Breeding purebred animals with unrelated purebred
animals.
Cross Breeding: Breeding animals of the same species but of a
different breed.
Hybrid Vigor or Heterosis:
 A biological phenomenon which causes crossbreeds to out
produce the average of their parents
 Will achieve 15 to 25% immediate increase in yield
 The more dissimilar the breeds, the greater the heterosis:
(British breed crossed with Zebu breed)
Infovets Educational Resources – www.infovets.com – Slide 8
Two-Breed Cross
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Purebred bulls X purebred cows of another breed
8-10% increase in weaning weight
Infovets Educational Resources – www.infovets.com – Slide 9
Two-Breed Backcross or Crisscross
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Breed A X Breed B = Crossbred calves
Crossbred X Breed A or B
Charolais Bull X Hereford Cow = Cross
Cross X Charolais
Yields 67% of maximum heterosis
Infovets Educational Resources – www.infovets.com – Slide 10
Three Breed Rotation Cross
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3 Breeds (Angus, Simmental, Charolais)
Crossbred females bred to purebred bull of breed A
Resulting cross mated to purebred bull of breed B
Resulting cross mated to purebred bull of breed C
Repeat rotation
87% of maximum heterosis
Infovets Educational Resources – www.infovets.com – Slide 11
Gene Transfer
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All selection is based on the concept that desired characteristics
are passed on from the parents to the offspring.
Humans have 46 chromosomes. Each parent contributes 23.
A chromosome is a long protein strand on molecules called DNA.
DNA is made up of segments called genes.
Infovets Educational Resources – www.infovets.com – Slide 12
Gene Transfer
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Each gene is responsible for a particular trait.
Genes form a code or a blueprint for how the animal is to be
formed.
One chromosome (strand of DNA) will attach to another forming
a spiral shape called a double helix.
Infovets Educational Resources – www.infovets.com – Slide 13
Gene Transfer
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Each half is bound together by substances called nucleotides.
There are four main nucleotides:
 Adenine
 Thiamine
 Guanine
 Cytosine
Infovets Educational Resources – www.infovets.com – Slide 14
Gene Transfer
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Nucleotides are shaped so that each substance can pair with one
particular nucleotide.
Adenine can only pair with thiamine.
Cytosine can only pair with guanine.
When cells undergo mitosis and divide, each half replicates itself
so two strands exactly alike are formed. (DNA replication).
Infovets Educational Resources – www.infovets.com – Slide 15
Gene Transfer
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The genetic sequence on the DNA is used as a pattern for how the
animal is to be constructed. RNA (Ribonucleic acid) reads the
pattern and transfers the information to the rest of the cell.
Infovets Educational Resources – www.infovets.com – Slide 16
Genetic Engineering
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Genetic engineering is a technology that allows specific genetic
information or traits to be built into or engineered into the genes of
a species.
In genetic engineering, segments of DNA are cut and spliced into
existing DNA, placing new genetic information into the existing
DNA.
Infovets Educational Resources – www.infovets.com – Slide 17
Differentiation
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As the embryo begins to grow and develop, cells differentiate.
Some cells develop into muscle and bone, some into skin and
some into internal organs.
The process of how cells differentiate is not fully understood.
Infovets Educational Resources – www.infovets.com – Slide 18
Differentiation
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Sex cells called gametes undergo meiosis and only carry one
strand of DNA.
At conception, chromosome halves from each parent combine to
form a paired chromosome.
There is almost an infinite number of ways that the genes can be
arranged on a strand of DNA. This arrangement determines the
make up of the new animal.
Infovets Educational Resources – www.infovets.com – Slide 19
Alleles
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Each male gene that controls a specific trait combines with the
female gene for the same trait.
A pair of genes that control a specific trait are called alleles.
If both genes that control a specific trait are alike, they are said to
be homozygous.
For example, if the male gene for hair color is black and the
female gene that controls hair color is also black.
Infovets Educational Resources – www.infovets.com – Slide 20
Gene Dominance
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If they are different (black & red), they are said to be
heterozygous.
In this case one gene will be dominate and determine coat color.
Dominant gene = trait overpowers others
Recessive gene = must be accompanied with another recessive
gene to express trait
Infovets Educational Resources – www.infovets.com – Slide 21
Gene Dominance
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P = polled
p = horned
Genotype is the genetic make up of the animal.
Phenotype is the physical appearance of the animal.
If a homozygous horned cow (pp) is mated to a homozygous
polled bull (PP), what will the genotypic and phenotypic ratio of
the calves be?
Infovets Educational Resources – www.infovets.com – Slide 22
Punnett Square
P
p
P p
p
P p
P
P p
P p
Infovets Educational Resources – www.infovets.com – Slide 23
Monohybrid Cross
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A monohybrid cross is an estimation of a predicted outcome for a
single trait.
If a homozygous horned cow (pp) is bred with a heterozygous
polled bull (Pp), what percent of the calves will be polled?
Infovets Educational Resources – www.infovets.com – Slide 24
Monohybrid Cross
P
p
P p
p
P p
P
P p
P p
Infovets Educational Resources – www.infovets.com – Slide 25
Monohybrid Cross
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What results if two heterozygous animals are mated.
Infovets Educational Resources – www.infovets.com – Slide 26
Dihybrid Cross
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A dihybrid cross is a estimation of a predicted outcome for two
traits.
What results if an Angus bull that is homozygous black and polled
(BBPP) is bred with a red shorthorn cow which is homozygous
red and horned (bbpp).
The bull BBPP can be simplified to BP (black & polled is the only
possible contribution for the bull).
The cow bbpp can be simplified to bp (red & horned is the only
possible contribution for the cow).
Infovets Educational Resources – www.infovets.com – Slide 27
Dihybrid Cross
bp
bp
B P
B P
B bPp
B bPp
B bPp
Black = 100%
Polled = 100%
Horned = 0%
B bPp
Infovets Educational Resources – www.infovets.com – Slide 28
Dihybrid Cross
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Now if two of the offspring which are heterozygous for black/red
and polled/horned (BbPp) are mated.
How do you do a Punnett square for two heterozyous animals?
Use all possible gene combinations.
Both the bull and cow are BbPp.
What are the possible contributions?
BP, Bp, bP, bp for both animals. (4 x 4 grid)
Infovets Educational Resources – www.infovets.com – Slide 29
Dihybrid Cross
BP
Bp
bP
bp
BP
BBPP
BBPp
BbPP
BbPp
Bp
BBpP
BBpp
BbPp
Bbpp
bbPp
bP
BbPP
BbPp
bbPP
bp
BbPp
Bbpp
bbPp
bbpp
Infovets Educational Resources – www.infovets.com – Slide 30
Dihybrid Cross
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Black Polled = 9 out of 16 or 56.25%
Black Horned = 3 out of 16 or 18.75%
Red Polled = 3 out of 16 or 18.75%
Red Horned = 1 out of 16 or 6.25%
Infovets Educational Resources – www.infovets.com – Slide 31
Dihybrid Cross
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If a heterozygous bull (BbPp) is mated to a homozygous cow
(BBPP).
What are the outcomes?
Infovets Educational Resources – www.infovets.com – Slide 32
Dihybrid Cross
B P
B P
B p
B B PP B B Pp
bP
B bPP
Infovets Educational Resources – www.infovets.com – Slide 33
bp
B bPp
Dihybrid Cross
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If a (BbPp) bull is mated to a (BBPp) cow.
what are the outcomes?
Infovets Educational Resources – www.infovets.com – Slide 34
Dihybrid Cross
BP
Bp
bP
bp
BP
B B PP
B B Pp
B bPP
B bPp
Bp
B B Pp
B B pp
B bPp
B bpp
Infovets Educational Resources – www.infovets.com – Slide 35
Mendilin Genetics
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Paint color is a desirable characteristic of paint horses and is
dominate to solid color.
If a homozygous dominate stallion is bred with a solid colored
mare, how likely is it that a paint foal will result?
What if the stallion is heterozygous for paint color?
Infovets Educational Resources – www.infovets.com – Slide 36
Codominate Genes
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Some alleles may have two dominate genes.
Shorthorn cattle are red, white or roan.
Red shorthorns carry the gene for red coat color RR.
White shorthorns carry the gene for white coat color WW.
Cattle that are roan or spotted carry a gene for red and a gene for
white RW.
Both are dominant, creating a spotted or roan colored animal.
Infovets Educational Resources – www.infovets.com – Slide 37
Shorthorn: Red X White
R
R
W
R
W
R
W
W
R
W
R
W
Infovets Educational Resources – www.infovets.com – Slide 38
The Additive Expression of Genes
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Instead of a single pair, a number of genes may be added together
to produce a single trait.
Examples:
Milk production is controlled by several genes.
 Size and body capacity of the female
 Hormone production
 Mammary size and function
Rate of gain
Reproduction
Infovets Educational Resources – www.infovets.com – Slide 39
Genetic Mutations
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Occasionally a defect will happen and genetic traits are not passed
on as intended.
Example: two headed calves
An abnormality is similar to a mutation, only it is caused by
something in the environment
Infovets Educational Resources – www.infovets.com – Slide 40
Genetic Mutations
Infovets Educational Resources – www.infovets.com – Slide 41
Genetic Mutations
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Sometimes genetic mutations can be used to introduce new kinds
of species.
Polled Hereford Cattle
Infovets Educational Resources – www.infovets.com – Slide 42
Determining an Animal’s Sex
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Whether a mammal is a male or a female is determined upon
conception.
Gamete (sex cell) contains one half of the sex chromosome from
the parent.
The female chromosome is referred to as XX.
When the chromosome divides and half goes to the offspring each
half is the same.
Infovets Educational Resources – www.infovets.com – Slide 43
Determining an Animals Sex
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The male chromosome is referred to as XY. And when divided, a
gamete will be either X or Y.
When the male and female gamete combine they will either be XX
female or XY male.
What is the probability of a male being conceived over a female
child?
Infovets Educational Resources – www.infovets.com – Slide 44
What Sex Will the Offspring Be?
X
X
X X
X
X X
Y
X Y
X Y
Infovets Educational Resources – www.infovets.com – Slide 45
Sex Determination
Infovets Educational Resources – www.infovets.com – Slide 46