Animal Genetics: A Comprehensive Overview
Animal Genetics
Genetics
The study of heredity or how traits are
passed from parents to offspring
Genetic Material
Chromosome
Rod shaped structure
in the nucleus of a
cell consisting of
genes
Occur in pairs except
in the reproductive
cells
Pairs of Chromosomes in
Livestock
DNA
Deoxyribonucleic acid
A nucleic acid containing the genetic
information for all living cells
Gene
A segment of
DNA, occupying a
specific place on
a chromosome,
that is the basic
unit of heredity
Allele
One of two or more forms of a gene
Nucleotide
The basic building block of DNA and RNA
Made up of nitrogenous base, a sugar,
and a phosphate group
Nucleic Acids
The main function is to store and transmit
genetic information and use that
information to direct the synthesis of new
protein.
Two types exist- DNA & RNA
RNA has 3 types with different functions
mRNA carries information from nucleus to
cytoplasm
tRNA carries amino acids
rRNA forms ribosomes
Three Types of Nucleic Acids
A Nitrogenous base
A Phosphate group
A 5-carbon sugar
Nitrogenous Bases
5 main bases divided into two
categories
Purines
Adenine
Guanine
Pyrimidine's
Thymine
Cytosine
Uracil
Phosphate Group
Same among all nucleotides
5-carbon sugar
Comes in two forms
Deoxyribose as found in DNA
Ribose as found in RNA
Purines vs. Pyrimidine's
Purines are double-ringed
Pyrimidine's are smaller and only
single ringed.
Proteins
Large molecules
made of amino
acids that are
essential to the
structure and
functioning of all
living cells
Codon
A sequence of
three nucleotides
that specifies amino
acid addition during
protein synthesis
Genetic Terminology
Trait
Characteristics
passed from
parents to
offspring
Dominant
An allele which masks the expression of
another allele at the same locus
Represented by a capital letter
Recessive
An allele that is masked by a dominant
allele and only causes a detectable
characteristic in an organism that has two
copies of that allele
Represented by a lower case letter
Dominant and Recessive Traits
in Livestock
Dominant
Polled cattle
Black Holstein or
Angus
Belted pattern in
swine
Trotting gait
Black Horse
Recessive
Horned cattle
Red Holstein or
Angus
Non-Belted
Pattern-swine
Pacing Gait
Chestnut horse
Heterozygous
A condition in which two different alleles
code for the same trait
One dominant AND one recessive
Homozygous
A condition in which two alleles for a
given gene are the same
Both dominant OR both recessive
Genotype and Phenotype
Genotype
Amount, order, and type of genes an
individual has
Genetic make-up of an individual (i.e.
heterozygous or homozygous)
Phenotype
Physical traits an individual expresses
Gamete
A reproductive cell
– sperm and egg
Breeding Generations
P Generation - parental generation
F
1
Generation - filial Generation
1
st
offspring of P generation
F
2
Generation - 2
nd
Filial Generation
Offspring of F
1
Generation
History of Genetics
Gregor Mendel
An Austrian scientist and monk who
demonstrated that the inheritance of
certain traits in pea plants follows
particular patterns
Known as the “father” of modern
genetics
Mendel’s Experiment
P Generation
Allowed different varieties of plants
(ex. purple or white flowers) to self
pollinate for several generations
All offspring displayed only one form
of a particular trait (purebred)
Crossbred the two strains of the P
generation
Resulted in all purple flowers
Self-pollination of F
1
Generation
Results in F
2
Generation
1 out of every 4 flowers was white
Mendel's Laws
Mendel’s Laws
Law of Segregation
Law of Independent Assortment
Law of Segregation
Every individual possesses a pair of alleles
for any particular trait
Each parent passes a randomly selected
copy (allele) of only one of these to its
offspring
When any individual produces gametes,
the copies of a gene separate so that
each gamete receives only one copy
(allele)
Law of Segregation
Law of Independent
Assortment
Separate genes for separate traits are
passed independently of one another from
parents to offspring
Different traits are inherited independently
of each other
Only true for genes that are not linked
Law of Independent
Assortment
Biologist have discovered that Mendel’s
laws are simplifications of processes that
are sometimes much more complex
However, they form a important
foundation for the science of genetics!
Non-Mendelian Inheritance
Heritability
The capacity of a trait to be passed down
from a parent to offspring
May lead to genetic improvement of
animals
Natural: survival of the fittest - adaptation
Artificial: animals with desirable traits are
selected for breeding programs
Highly Heritable Livestock Traits
Carcass traits
Ribeye area
Backfat thickness
Percentage of muscle
Scrotal circumference
Marbling score
Tenderness score
Low Heritability Livestock Traits
Number of offspring
(hogs and sheep)
Weaning weight
Conception rate
Calving interval
Heritability Rates
Estimated Percent Heritability
Agriscience Fundamentals & Applications
Environmental Influence
Most traits are a combination of selection
and environment
External environment includes temperature,
light, altitude, humidity, disease, and feed
supply
Feed supply is the most important
environmental factor
Environmental Influence Cont’d
Environmental impact may influence the
degree to which genetic improvement can
be made through selection
An animal must have a suitable
environment to reach its genetic potential
Larger environmental influence of
production traits results in lower genetic
improvement due to selection
X and Y Chromosomes
Determines sex of animal
Females= XX
*bird eggs=XY
Males=XY b
*bird species sperm=XX
Males may contribute
either an X OR Y
chromosome –
determining the sex of
offspring
Sex Determination
Male Gametes
F
e
m
a
l
e
G
a
m
e
t
e
s
Sex-linked Traits
Traits determined by an allele located on a
sex chromosome
Most are located on the X chromosome
Longer and carries more genes
Called x – linked trait
Maternally inherited from carrier mothers
(a person who carries an allele without
exhibiting its effects, such an allele is
usually recessive) or from infected fathers
Sex-linked Traits
More common in
males due to their
heterozygous (XY)
state
If they receive an X
chromosome with
the trait they will
express that trait.
Females express the
recessive condition
only if she inherits
two recessive alleles
Sex-linked Traits in Animals
Calico fur color in domestic cats
Orange/black color gene is carried on the X
chromosome
Orange is dominant to black, but when
present in conjunction with the recessive
black allele a patchwork of orange and
black appear
Incomplete Dominance
One allele for a specific trait is not
completely dominant over the other allele
in a heterozygous individual
Results in an intermediate phenotype
A Hampshire pig crossed with a Yorkshire
results in a Blue Butt.
Codominance
Two alleles are fully expressed at the same
time in a heterozygote
Roan coat in cattle and horses
A cross between a homozygous red animal and
a homozygous white results in heterozygous
offspring with red and white hairs in about equal
numbers
Polygenic Trait
Traits controlled by two or more genes at
different loci on different chromosomes
Allow a wide range of physical traits
Examples include coat color, white
markings, growth rate, fertility, and carcass
merit
All of these characteristics have a degree
of intermediate conditions between one
extreme and the other
Heterosis
Performance of offspring that is greater
then the average of the parents - hybrid
vigor
Heterozygotes possess greater vigor or are
more desirable
Greater milk production, faster growth,
etc…
Often occurs when different purebred
animals are bred together.
Black Angus cow bred to a Hereford bull
Genetics and Probability
The Punnett Square
Diagram used to predict an outcome of
a particular cross or breeding experiment
Gives the correct probabilities for the
genotype outcomes
Setting Up The Punnett Square
Draw a 2 x 2 table
Write the genotype of one parent across the
top and that of the other parent down the left
side
Only one letter goes in each box for the
parents
B
B
b
b
Setting Up The Punnett Square
Fill in the boxes by copying the row and
column-head letters across or down into the
empty squares
Capital letters should be written first
This gives the predicted frequency of the
potential genotypes
B
B
b
b
B
b
B
b
b
b
B
B
Example
Mating sheep heterozygous for the
dominant trait white wool
Genotypic ratio 1:2:1
1Homozygous dominant: 1heterozygous:
1homozygous recessive
Phenotypic ratio 3:1
Three white sheep, one black sheep
Example
Heterozygous sheep mated with
homozygous dominant (trait white wool)
1:1 genotypic ratio
50% homozygous dominant and 50%
heterozygous
All offspring are white
Dihybrid Crosses: Multiple
Gene pairs
Determine the probability of genotypes
given two traits
i.e. red or black coat color
and
polled or
horned cattle
Setting Up The Punnett Square
Draw a 4 x 4 table
Setting Up The Punnett Square
Determine possible allele combinations for
parents
Remember the Law of Independent
Assortment
Example: cross two heterozygous black polled
individuals: BbPp x BbPp
Each allele will segregate independently
creating these combinations: BP, Bp, bP, bp
Setting Up The Punnett Square
Write the allele combinations of one parent
across the top and the other down the side
BP
BP
Bp
Bp
bP
bp
bP
bp
Setting Up The Punnett Square
Combine allele combinations across and down for
each box. Remember to keep like letters together
and write the capital letter first.
BP
BP
Bp
Bp
bP
bp
bP
bp
Dihybrid Cross Ratio
B = black coat
b=red coat
P = polled
p=horned
Phenotypic ratio is 9:3:3:1
9 black, polled: 3 black, horned: 3 red,
polled: 1 red, horned
Typical for dihybrid crosses
Resources
Scientific Farm Animal Production: An
Introduction to Animal Science; Robert E.
Taylor; Thomas G. Field
http://www.biologylessons.sdsu.edu/ta/cl
asses/lab6/TG.html
http://www.angelfire.com/clone2/nucleic
_acids/functions.htm
http://www.ansci.umn.edu/beef/beefup
dates/bcmu03.pdf
Animal genetics is the study of heredity, inheritance of traits from parents to offspring, genetic material like DNA, chromosomes, genes, alleles, and nucleotides. It involves the understanding of chromosomes in different livestock species, DNA as the carrier of genetic information, genes as units of heredity, alleles as gene forms, nucleotides as DNA building blocks, and nucleic acids' role in genetic information storage and protein synthesis. Discover the significance of nitrogenous bases and phosphate groups in nucleic acids, essential components for DNA and RNA.
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Presentation Transcript
Genetics The study of heredity or how traits are passed from parents to offspring
Chromosome Rod shaped structure in the nucleus of a cell consisting of genes Occur in pairs except in the reproductive cells
Pairs of Chromosomes in Livestock Livestock Species Turkeys Chickens Horses Cattle Goats Sheep Swine Humans Pairs of Chromosomes 41 39 32 30 30 27 19 23
DNA Deoxyribonucleic acid A nucleic acid containing the genetic information for all living cells
Gene A segment of DNA, occupying a specific place on a chromosome, that is the basic unit of heredity
Allele One of two or more forms of a gene
Nucleotide The basic building block of DNA and RNA Made up of nitrogenous base, a sugar, and a phosphate group
Nucleic Acids The main function is to store and transmit genetic information and use that information to direct the synthesis of new protein. Two types exist- DNA & RNA RNA has 3 types with different functions mRNA carries information from nucleus to cytoplasm tRNA carries amino acids rRNA forms ribosomes
Three Types of Nucleic Acids A Nitrogenous base A Phosphate group A 5-carbon sugar
Nitrogenous Bases 5 main bases divided into two categories Purines Adenine Guanine Pyrimidine's Thymine Cytosine Uracil
Phosphate Group Same among all nucleotides
5-carbon sugar Comes in two forms Deoxyribose as found in DNA Ribose as found in RNA
Purines vs. Pyrimidine's Purines are double-ringed Pyrimidine's are smaller and only single ringed.
Proteins Large molecules made of amino acids that are essential to the structure and functioning of all living cells
Codon A sequence of three nucleotides that specifies amino acid addition during protein synthesis
Trait Characteristics passed from parents to offspring
Dominant An allele which masks the expression of another allele at the same locus Represented by a capital letter
Recessive An allele that is masked by a dominant allele and only causes a detectable characteristic in an organism that has two copies of that allele Represented by a lower case letter
Dominant and Recessive Traits in Livestock Dominant Polled cattle Black Holstein or Angus Belted pattern in swine Trotting gait Black Horse Recessive Horned cattle Red Holstein or Angus Non-Belted Pattern-swine Pacing Gait Chestnut horse
Heterozygous A condition in which two different alleles code for the same trait One dominant AND one recessive
Homozygous A condition in which two alleles for a given gene are the same Both dominant OR both recessive
Genotype and Phenotype Genotype Amount, order, and type of genes an individual has Genetic make-up of an individual (i.e. heterozygous or homozygous) Phenotype Physical traits an individual expresses
Gamete A reproductive cell sperm and egg
Breeding Generations P Generation - parental generation F1 Generation - filial Generation 1stoffspring of P generation F2Generation - 2ndFilial Generation Offspring of F1Generation
Gregor Mendel An Austrian scientist and monk who demonstrated that the inheritance of certain traits in pea plants follows particular patterns Known as the father of modern genetics
Mendels Experiment P Generation Allowed different varieties of plants (ex. purple or white flowers) to self pollinate for several generations All offspring displayed only one form of a particular trait (purebred) Crossbred the two strains of the P generation Resulted in all purple flowers
Self-pollination of F1Generation Results in F2Generation 1 out of every 4 flowers was white
Mendels Laws Law of Segregation Law of Independent Assortment
Law of Segregation Every individual possesses a pair of alleles for any particular trait Each parent passes a randomly selected copy (allele) of only one of these to its offspring When any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy (allele)
Law of Independent Assortment Separate genes for separate traits are passed independently of one another from parents to offspring Different traits are inherited independently of each other Only true for genes that are not linked
Law of Independent Assortment
Biologist have discovered that Mendels laws are simplifications of processes that are sometimes much more complex However, they form a important foundation for the science of genetics!
Heritability The capacity of a trait to be passed down from a parent to offspring May lead to genetic improvement of animals Natural: survival of the fittest - adaptation Artificial: animals with desirable traits are selected for breeding programs
Highly Heritable Livestock Traits Carcass traits Ribeye area Backfat thickness Percentage of muscle Scrotal circumference Marbling score Tenderness score
Low Heritability Livestock Traits Number of offspring (hogs and sheep) Weaning weight Conception rate Calving interval
Heritability Rates Estimated Percent Heritability Trait Cattle Sheep Swine Fertility 0 - 10 0 - 15 0 - 15 Weight of young at weaning 15 - 30 15 - 20 15 - 20 Postweaning rate of gain Fat Thickness over loin Loin-eye Area 50 55 50 - 60 25 - 30 40 - 50 -------- 40 - 50 50 - 70 -------- 45 - 50 Percent lean cuts 40 - 50 -------- 30 - 40 Agriscience Fundamentals & Applications
Environmental Influence Most traits are a combination of selection and environment External environment includes temperature, light, altitude, humidity, disease, and feed supply Feed supply is the most important environmental factor
Environmental Influence Contd Environmental impact may influence the degree to which genetic improvement can be made through selection An animal must have a suitable environment to reach its genetic potential Larger environmental influence of production traits results in lower genetic improvement due to selection
X and Y Chromosomes Determines sex of animal Females= XX *bird eggs=XY Males=XY b *bird species sperm=XX Males may contribute either an X OR Y chromosome determining the sex of offspring
Sex Determination Male Gametes X Y X XX XY Gametes Female X XX XY
Sex-linked Traits Traits determined by an allele located on a sex chromosome Most are located on the X chromosome Longer and carries more genes Called x linked trait Maternally inherited from carrier mothers (a person who carries an allele without exhibiting its effects, such an allele is usually recessive) or from infected fathers
Sex-linked Traits More common in males due to their heterozygous (XY) state If they receive an X chromosome with the trait they will express that trait. Females express the recessive condition only if she inherits two recessive alleles
Sex-linked Traits in Animals Calico fur color in domestic cats Orange/black color gene is carried on the X chromosome Orange is dominant to black, but when present in conjunction with the recessive black allele a patchwork of orange and black appear
