Transcript animal genetics

ANIMAL
GENETICS
Agriscience 332
Animal Science
#8406
TEKS: (c)(4)(B)
Illustration of DNA
Double Helix from
Wikipedia.
Introduction
Genetics is the science of
heredity and variation.
It is the scientific discipline
that deals with the differences
and similarities among related
individuals.
Illustration of DNA
Double Helix from
Wikipedia.
All animals have a
predetermined genotype that
they inherit from their parents.
However, an animal’s genotype
can be manipulated by
breeding and more advanced
scientific techniques (genetic
engineering and cloning).
Illustration of DNA
Double Helix from
Wikipedia.
For many years, managers of
agricultural systems have
manipulated the genetic makeup
of animals to improve productivity
and increase efficiency.
Illustration of DNA
Double Helix from
Wikipedia.
Successful manipulation of the
genetic composition of animals
requires an understanding of
some fundamental principles of
genetics.
Mendelian Genetics
Gregor Mendel is
recognized as the
father of genetics.
Mendel, who was not
scientifically trained, developed
his theories in the 1850’s and
1860’s, without any knowledge of
cell biology or the science of
inheritance.
Photo courtesy of Wikipedia.
Illustration of DNA
Double Helix from
Wikipedia.
In later years, genes,
chromosomes, and DNA were
discovered and people began
to understand how and why
Mendel’s theories worked.
Illustration of DNA
Double Helix from
Wikipedia.
Mendel proposed three principles
to describe the transfer of
genetic material from one
generation to the next.
• The Principle of Dominance
• The Principle of Segregation
• The Principle of Independent
Assortment
Illustration of DNA
Double Helix from
Wikipedia.
The Principle of Dominance – in
a heterozygous organism, one
allele may conceal the presence
of another allele.
Illustration of DNA
Double Helix from
Wikipedia.
The Principle of Segregation –
in a heterozygote, two different
alleles segregate from each other
during the formation of gametes.
Illustration of DNA
Double Helix from
Wikipedia.
The Principle of Independent
Assortment – the alleles of
different genes segregate, or
assort, independently of each
other.
Illustration of DNA
Double Helix from
Wikipedia.
Later studies have shown that
there are some important
exceptions to Mendel’s Principle
of Independent Assortment, but
otherwise, these principles are
recognized as the basis of
inheritance.
Illustration of DNA
Double Helix from
Wikipedia.
Mendel’s experiments dealt with
the relationship between an
organism’s genotype and its
phenotype.
Genotype – the genetic
composition of an organism.
Illustration of DNA
Double Helix from
Wikipedia.
Phenotype – the observable or
measurable characteristics
(called traits) of that organism.
Two organisms may appear to be
similar, but they can have
different genotypes.
Similarly, two animals may have
the same genotypes, but will
appear to be different from each
other, if they have been exposed
to different environmental
conditions throughout their lives.
Illustration of DNA
Double Helix from
Wikipedia.
The relationship between
phenotype and genotype is
expressed as the following
equation:
P=G+E
P = phenotype,
G = genotype, and
E = environment.
Illustration of DNA
Double Helix from
Wikipedia.
If two individuals with identical
genotypes are exposed to the
same environmental conditions,
such as nutrition, climate, and
stress levels, their phenotypes
(measurable and observable
characteristics) should be the
same.
Illustration of DNA
Double Helix from
Wikipedia.
To understand Mendel’s
principles and the relationships
between phenotype and
genotype, it is necessary to
understand what makes up the
genetic material of animals
and how this is transferred
from one generation to the
next.
Illustration of DNA
Double Helix from
Wikipedia.
Genetic Material
The body is made up of millions
of cells which have a very
complicated structure.
These cells are made up of many
parts that have specialized roles.
Illustration of DNA
Double Helix from
Wikipedia.
Courtesy of Wikipedia
Illustration of DNA
Double Helix from
Wikipedia.
1. Nucleolus
5. Rough Endoplasmic Reticulum
9. Mitochondria
2. Nucleus
6. Golgi Aparatus
10. Vacuole
3. Ribosome
7. Cytoskeleton
11. Cytoplasm
4. Vesicle
8. Smooth Endoplasmic Reticulum
12. Lysosome
13. Centrioles
The nucleus contains
chromosomes that are visible
under the microscope as darkstaining, rod-like or rounded
bodies.
Illustration of DNA
Double Helix from
Wikipedia.
Chromosomes occur in pairs in
the body cells.
The number of chromosomes
in each cell is constant for
individual species, but it differs
among species.
Illustration of DNA
Double Helix from
Wikipedia.
Chromosomes are made up of
tightly-coiled strands of DNA.
DNA is a complex molecule
composed of deoxyribose,
phosphoric acid, and four bases.
Individual genes are located in
a fixed position (known as the
loci) on the strands of DNA.
Illustration of DNA
Double Helix from
Wikipedia.
A Chromosome
A chromosome is made up of two chromatids and a centromere. The
chromatids are formed from tightly coiled strands of DNA. If these
strands of DNA are stretched out, individual genes can be identified.
Illustration of DNA
Double Helix from
Wikipedia.
A gene is made up of a specific
functional sequence of nucleotides,
which code for specific proteins.
A specific protein is
produced when the
appropriate apparatus
of the cell
(the ribosome)
reads the code.
Illustration of DNA
Double Helix from
Wikipedia.
Image courtesy of Wikipedia.
The collection of
genes that an
organism has is
called its
genome.
Photo by Peggy Greb courtesy of USDA Agricultural Research Service.
Illustration of DNA
Double Helix from
Wikipedia.
In somatic cells (body cells),
chromosomes occur in pairs,
known as homologous
chromosomes.
As a result, genes also occur in
pairs.
Somatic cells are referred to as
diploid, or 2n.
Illustration of DNA
Double Helix from
Wikipedia.
Gametes (reproductive cells) do not
have paired chromosomes and are
referred to as haploid, or n.
Illustration of DNA
Double Helix from
Wikipedia.
Cell Division
Cells must divide and increase
in number so that animals can
grow.
A new cell is formed when one
cell divides.
Mitosis and meiosis are the two
processes by which cells divide.
Illustration of DNA
Double Helix from
Wikipedia.
Mitosis is the type of cell
division in which the genetic
material in the parent cell is
duplicated and then divides
into two separate cells with
identical genetic material.
Illustration of DNA
Double Helix from
Wikipedia.
Both new cells are diploid (2n)
with a complete set of
chromosomes identical to
those in the parent cell.
Image courtesy of Wikepedia.
Illustration showing stages of cell cycle:
Interphase – portion of cell cycle in which
the cell grows then replicates DNA.
Mitosis – portion of cell cycle in which division
of the cell takes place; includes Prophase,
Metaphase, Anaphase, and Telaphase.
Illustration of DNA
Double Helix from
Wikipedia.
Meiosis is the process of cell
division that occurs in
reproductive cells (sperm and
egg).
In this type of division, the
chromosome number is halved
from the diploid number (2n)
to the haploid number (n).
Illustration of DNA
Double Helix from
Wikipedia.
If gametes were diploid cells,
the number of chromosomes
would double with each
generation.
Meiosis ensures that gametes
receive only one-half the
number of chromosomes that
are present in parent cells.
Illustration of DNA
Double Helix from
Wikipedia.
Fertilization
Fertilization is the process of
joining the male gamete with
the female gamete.
Illustration of DNA
Double Helix from
Wikipedia.
Photo from Wikipedia.
All animals originate from the
union of a single haploid cell
from the female (ovum or egg)
and a single haploid cell from the
male (spermatozoa or sperm).
The result of this union is a
zygote (diploid cell), which
develops into a new animal with
a full set of chromosomes.
Illustration of DNA
Double Helix from
Wikipedia.
When discussing different
generations in genetics, the first
generation is referred to as the
parent or P generation.
Their offspring are referred to as
the first filial or F1 generation.
P
Illustration of DNA
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Wikipedia.
F1
X
F1
P
F1
F1
When individuals from the F1
generation are mated with each
other, their offspring are
referred to as the F2 generation.
F1
F2
Illustration of DNA
Double Helix from
Wikipedia.
X
F2
F1
F2
F2
Principle of Dominance
In animals, chromosomes are
paired and, therefore, genes
are paired.
These paired genes code for
the same trait, but they are
not identical.
Illustration of DNA
Double Helix from
Wikipedia.
They can have different forms,
known as alleles.
For example, sheep and cattle
can be polled or horned.
One gene codes
for this trait and
the two possible
forms (alleles)
of the gene are
polled or horned.
Illustration of DNA
Double Helix from
Wikipedia.
Photo from IMS.
USDA photo from Wikipedia.
A capital letter is used to denote
the dominant form of the gene
(P) and a small letter is used to
denote the recessive form of the
gene (p).
Illustration of DNA
Double Helix from
Wikipedia.
In the example, the polled allele
is dominant and is, therefore,
denoted by P, while the horned
allele is recessive and denoted
by p.
Because genes are paired, an
animal can have three different
combinations of the two alleles:
PP,
Pp, or
pp.
Illustration of DNA
Double Helix from
Wikipedia.
When both genes in a pair take
the same form (PP or pp), the
animal is referred to as being
homozygous for that trait.
An animal with a PP genotype is
referred to as homozygous
dominant.
Illustration of DNA
Double Helix from
Wikipedia.
An animal with the pp genotype
is referred to as homozygous
recessive.
If one gene in the pair is the
dominant allele (P) and the
other gene is the recessive
allele (p), the animal is referred
to as being heterozygous for
that trait and its genotype is
denoted as Pp.
Illustration of DNA
Double Helix from
Wikipedia.
Genotype refers to the actual
genetic makeup.
Phenotype refers to the physical
expression of the genes.
If an animal has the allele
combination PP, it will be polled.
If the combination is pp, the
animal will be horned.
Illustration of DNA
Double Helix from
Wikipedia.
If it is a heterozygote, then
genotypically the animal will
have both traits (Pp), but
phenotypically the animal will
be polled because the polled
allele (P) is the dominant form
of the gene.
Illustration of DNA
Double Helix from
Wikipedia.
Mendel’s principle of dominance
states that in a heterozygote,
one allele may conceal the
presence of another.
Illustration of DNA
Double Helix from
Wikipedia.
In this example, the polled allele
is concealing the horned allele
and, therefore, is referred to as
the dominant allele.
Illustration of DNA
Double Helix from
Wikipedia.
Principle of Segregation
When animals reproduce, they
only pass on half of their genetic
material to their offspring
because gametes, or
reproductive cells, only have one
chromosome from each pair.
The offspring will only receive
one allele from each parent.
Illustration of DNA
Double Helix from
Wikipedia.
The Principle of Segregation
explains some of the differences
that are observed in successive
generations of animals and can
be used to predict the probability
of different combinations of
alleles occurring in offspring.
Illustration of DNA
Double Helix from
Wikipedia.
As previously discussed, three
kinds of individuals are possible
when describing a pair of genes:
• Homozygous dominant (PP),
• Homozygous recessive (pp),
and
• Heterozygous (Pp).
Illustration of DNA
Double Helix from
Wikipedia.
Considering these three types of
individuals, six combinations of
the various genotypes are
possible:
• PP x PP (both parents are
homozygous polled),
• PP x Pp (one homozygous
polled parent and one
heterozygous polled parent),
Illustration of DNA
Double Helix from
Wikipedia.
• PP x pp (one homozygous
polled parent and one
homozygous horned parent),
• Pp x Pp (both parents are
heterozygous polled),
• Pp x pp (one heterozygous
polled parent and one
homozygous horned parent),
and
Illustration of DNA
Double Helix from
Wikipedia.
• pp x pp (both parents are
homozygous horned).
The genotypes of the parents
can be used to predict the
phenotypes of the offspring.
Illustration of DNA
Double Helix from
Wikipedia.
Predicting the Genotypes
and Phenotypes of Offspring
A punnett square is a grid-like
method that is used to display
and predict the genotypes and
phenotypes of offspring from
parents with specific alleles.
Illustration of DNA
Double Helix from
Wikipedia.
The male genotype is normally
indicated at the top and the
female genotype is indicated in
the vertical margin.
Illustration of DNA
Double Helix from
Wikipedia.
When crossing homozygous
dominant parents (PP x PP), all
offspring will be homozygous
dominant polled individuals.
Illustration of DNA
Double Helix from
Wikipedia.
When crossing homozygous
recessive parents (pp x pp), all
of the offspring will be horned
(homozygous recessive)
individuals.
Illustration of DNA
Double Helix from
Wikipedia.
When crossing a heterozygous
parent with a homozygous
dominant parent (Pp x PP), the
expected offspring would occur
in a 1:1 ratio of homozygous
dominant to heterozygous
individuals.
Phenotypically, all offspring
would be polled.
Illustration of DNA
Double Helix from
Wikipedia.
When crossing a homozygous
dominant parent with a
homozygous recessive parent
(PP x pp), all offspring would be
heterozygous and polled.
Illustration of DNA
Double Helix from
Wikipedia.
Illustration of DNA
Double Helix from
Wikipedia.
When crossing a heterozygous
parent with a homozygous
recessive parent (Pp x pp), the
offspring would occur in a
genotypic ratio of 1:1 for
heterozygous to homozygous
recessive.
About one-half of the offspring
would be polled.
Illustration of DNA
Double Helix from
Wikipedia.
Illustration of DNA
Double Helix from
Wikipedia.
If two heterozygous parents are
crossed (Pp x Pp), one can
expect a genotypic ratio of 1:2:1,
with one homozygous dominant
polled, two heterozygous polled,
and one homozygous recessive
horned individuals.
Illustration of DNA
Double Helix from
Wikipedia.
The expected phenotypic ratio of
offspring would be 3:1 (polled to
horned).
Illustration of DNA
Double Helix from
Wikipedia.
Considering Multiple Traits
Commonly, there are multiple
traits that need to be considered
when mating animals.
For example, consider that cattle
can be horned or polled and
white-faced or red-faced.
Illustration of DNA
Double Helix from
Wikipedia.
The horns and red-faced
coloring are recessive traits.
If two individuals with two pairs
of heterozygous genes (each
affecting a different trait) are
mated, the expected genotypic
and phenotypic ratios would be:
Genotypes – 1 PPWW, 2 PPWw,
2 PpWW, 4 PpWw, 1 PPww,
2 Ppww, 1 ppWW, 2 ppWw, and
1 ppww;
Illustration of DNA
Double Helix from
Wikipedia.
Phenotypes – 9 polled, whitefaced; 3 polled, red-faced; 3
horned, white-faced; and 1
horned, red-faced offspring.
Illustration of DNA
Double Helix from
Wikipedia.
Illustration of DNA
Double Helix from
Wikipedia.
The Law of Independent
Assortment
When considering multiple
traits, Mendel hypothesized that
genes for different traits are
separated and distributed to
gametes independently of one
another.
Illustration of DNA
Double Helix from
Wikipedia.
Therefore, when considering
polled and white-faced traits,
Mendel assumed that there
was no relationship between
how they were distributed to
the next generation.
Illustration of DNA
Double Helix from
Wikipedia.
In most cases, genes do assort
independently.
However, advances in genetics
have shown that an abnormal
situation, called crossing-over,
can occur between genes for
different traits.
Illustration of DNA
Double Helix from
Wikipedia.
Crossing-over is an exchange of
genes by homologous
chromosomes during the
synapses of meiosis prior to the
formation of
the sex cells
or gametes.
Thomas Hunt Morgan’s illustration (1916) courtesy of Wikipedia.
Illustration of DNA
Double Helix from
Wikipedia.
Other Concepts in
Genetics
Non-traditional inheritance
involves alleles that are not
dominant or recessive.
Illustration of DNA
Double Helix from
Wikipedia.
Incomplete, or partial dominance,
and co-dominance are two
examples of non-traditional
inheritance.
Partial (Incomplete)
Dominance
Partial, or incomplete,
dominance occurs when the
heterozygous organism exhibits
a trait in-between the dominant
trait and the recessive trait.
Illustration of DNA
Double Helix from
Wikipedia.
Partially dominant alleles for
color are seen in several
species of flowers and in mice.
Ex. Homozygous mice are
black (BB) or white (bb) and
the heterozygous mice will be
grey (Bb).
Illustration of DNA
Double Helix from
Wikipedia.
Sheep exhibit incomplete
dominance in the trait for eye
color.
When a pure, brown-eyed
sheep is crossed with a pure,
green-eyed sheep, blue-eyed
offspring are produced.
Illustration of DNA
Double Helix from
Wikipedia.
Codominance
Codominance occurs when a
heterozygote offspring exhibits
traits found in both associated
homozygous individuals.
An example of codominance is
the feather color of chickens.
Illustration of DNA
Double Helix from
Wikipedia.
If a homozygous black rooster
is mated to a homozygous
white hen, the heterozygous
offspring would have both black
feathers and white feathers.
Illustration of DNA
Double Helix from
Wikipedia.
Roan is a coat color in horses
(sometimes dogs and cattle) that
is a mixture of base coat colored
hairs (ex. black, chestnut) and
white hairs.
Neither the base coat color or
the white hairs are dominant nor
do they blend to create an
intermediate color.
Illustration of DNA
Double Helix from
Wikipedia.
The roan animal actually has
both colored and white hairs.
Illustration of DNA
Double Helix from
Wikipedia.
Photo courtesy of Wikipedia.
Under these circumstances,
neither allele is dominant and
neither is recessive.
Therefore, each allele is
denoted by a capital letter.
Illustration of DNA
Double Helix from
Wikipedia.
Epistasis
(Polygenic Inheritance)
It is possible for more than
one gene to control a single
trait.
This type of interaction
between two nonallelic genes
is referred to as epistasis.
Illustration of DNA
Double Helix from
Wikipedia.
When two or more genes
influence a trait, an allele of one
of them may have an epistatic,
or overriding, effect on the
phenotype.
Comb shape in chickens is an
example of an epistatic
relationship.
Illustration of DNA
Double Helix from
Wikipedia.
Domestic chickens can have four
different types of comb shapes:
(a) rose, (b) pea, (c) walnut, and
(d) single.
Illustration of DNA
Double Helix from
Wikipedia.
Comb shape is influenced by
two independently assorting
genes, R and P, each with two
alleles.
Wyandotte chickens with rose
combs have the genotype
RRpp,while the Brahma chickens
with pea combs have the
genotype rrPP.
Illustration of DNA
Double Helix from
Wikipedia.
The F1 hybrids between these
two varieties are RrPp;
phenotypically, they have walnut
combs.
If those hybrids are intercrossed
with each other, all four types of
combs appear in the progeny in
a ratio of 9:3:3:1 for
walnut:rose:pea:single.
Illustration of DNA
Double Helix from
Wikipedia.
Illustration of DNA
Double Helix from
Wikipedia.
Mutations and Other
Chromosomal Abnormalities
Genes have the capability of
duplicating themselves, but
sometimes a mistake is made
in the duplication process
resulting in a mutation.
Illustration of DNA
Double Helix from
Wikipedia.
The new gene created by this
mutation will cause a change in
the code sent by the gene to
the protein formation process.
Some mutations cause defects
in animals, while others may be
beneficial.
Illustration of DNA
Double Helix from
Wikipedia.
Mutations are responsible for
variations in coat color, size,
shape, behavior, and other
traits in several species of
animals.
The beneficial mutations are
helpful to breeders trying to
improve domestic animals.
Illustration of DNA
Double Helix from
Wikipedia.
Changes that can occur in
chromosomes during meiosis
include:
• Nondisjunction – chromosome
number,
• Translocation or deletion –
chromosome breakage, and
Illustration of DNA
Double Helix from
Wikipedia.
• Inversion – the rearrangement
of genes on a chromosome.
Changes in chromosomes are
reflected in the phenotypes of
animals.
Some chromosomal changes will
result in abnormalities, while
others are lethal and result in
the death of an animal shortly
after fertilization, during prenatal
development, or even after birth.
Illustration of DNA
Double Helix from
Wikipedia.
Sex-Linked Traits
Sex-linked traits involve genes
that are carried only on the
X or Y chromosomes, which are
involved in determining the sex
of animals.
The female genotype is XX,
while the male genotype is XY.
Illustration of DNA
Double Helix from
Wikipedia.
The X chromosome is larger and
longer than the Y chromosome,
which means a portion of the X
chromosome does not pair with
genes on the Y chromosome.
Illustration of DNA
Double Helix from
Wikipedia.
Additionally, a certain portion of
the Y chromosome does not link
with the X chromosome.
The traits on this portion of the
Y chromosome are transmitted
only from fathers to sons.
Illustration of DNA
Double Helix from
Wikipedia.
Sex-linked traits are often
recessive and are covered up in
the female mammal by
dominant genes.
The expression of certain genes,
which are carried on the regular
body chromosomes of animals,
is also affected by the sex of the
animal.
The sex of an animal may
determine whether a gene is
dominant or recessive (Ex. Scurs
in polled European cattle).
Illustration of DNA
Double Helix from
Wikipedia.
In poultry, the male has the
genotype XX, while the female
has the genotype Xw.
An example of a sex-linked
trait in poultry is the barring of
Barred Plymouth Rock
chickens.
Illustration of DNA
Double Helix from
Wikipedia.
If barred hens are mated to
non-barred males, all of the
barred chicks from this cross are
males, and the non-barred
chicks are females.
Illustration of DNA
Double Helix from
Wikipedia.
Photo courtesy of Wikipedia.
Genetic Selection
Permanent improvements in
domestic animals can be made
by genetic selection through
natural or artificial means.
Illustration of DNA
Double Helix from
Wikipedia.
Natural selection occurs in
wild animals, while artificial
selection is planned and
controlled by humans.
Animals that exhibit desirable
traits are selected and mated.
Animals that exhibit undesirable
traits are not allowed to reproduce
or are culled from the herd.
“Geneticist Michael
MacNeil examines results
from genetic analysis of
sires used in the Angus
Sire Alliance program at
Circle A Angus Ranch.
Economic values for
individual traits are used
to sort bulls by potential
profitability of their
offspring” (USDA – ARS).
Illustration of DNA
Double Helix from
Wikipedia.
Photo by Peggy Greb courtesy of USDA Agricultural Research Service.
The goal of selection is to
increase the number of animals
with optimal levels of
performance, while culling
individuals with poorer
performance.
Illustration of DNA
Double Helix from
Wikipedia.
Genetic improvement is a slow
process and can take several
generations to see an
improvement in a trait.
Artificial insemination and
embryo transfer are breeding
methods that are commonly used
to decrease the time taken to
improve a trait.
“Angus surrogate mother
nurses her Romosinuano
embryo transfer calf.
Initially, scientists are
investigating the
influence of surrogate
breed on Romosinuano
calf traits such as length
of gestation and birth
and weaning weights”
(USDA-ARS)
Illustration of DNA
Double Helix from
Wikipedia.
Photo by Scott Bauer courtesy of USDA Agricultural Research Service.
Traits are passed from parents
to offspring, but some traits are
more heritable than other
traits.
That is, the genotype of an
individual will be expressed
more strongly and environment
will be less influential for
particular traits.
Illustration of DNA
Double Helix from
Wikipedia.
Heritability of Various Traits in Livestock
Trait
Illustration of DNA
Double Helix from
Wikipedia.
Sheep
Swine
Cattle
Weaning weight
15-25%
15-20%
15-27%
Post-weaning gain
efficiency
Post-weaning rate of gain
20-30%
20-30%
40-50%
50-60%
25-30%
50-55%
Feed efficiency
50%
12%
44%
Loin eye area
53%
53%
56%
Several genes influence some
traits.
For example,
rate of growth
is a trait that is
influenced by
appetite,
energy expenditure,
feed efficiency, and
body composition.
Photo by Brian Prechtel courtesy of USDA Agricultural Research Service.
Illustration of DNA
Double Helix from
Wikipedia.
Breeding systems aim to
improve a single trait or multiple
traits.
Single trait selection – aimed at
improving one trait in a breeding
program with little or no regard
for improvement in other
(associated) traits.
Illustration of DNA
Double Helix from
Wikipedia.
Multiple trait selection – aims to
simultaneously improve a
number of traits.
Theoretically, multiple trait
selection should result in a faster
rate of gain toward a specific
objective.
Illustration of DNA
Double Helix from
Wikipedia.
Most domestic species now have
a recognized system in place
that allows breeders to estimate
the genetic merit of individuals.
In the United States, cattle,
sheep, goat, and swine breeders
use expected progeny
differences (EPDs).
Illustration of DNA
Double Helix from
Wikipedia.
EPDs are used to compare
animals from the same species
and breed.
“Newly developed
EPDs (expected
progeny differences)
make it possible to
select for tenderness
and carcass and beef
quality traits in
Brahman cattle,
shown here at the
ARS Subtropical
Agricultural Research
Station in Brooksville,
Florida” (USDA-ARS).
Photo by David Riley courtesy of USDA Agricultural Research Service.
Illustration of DNA
Double Helix from
Wikipedia.
For EPD values to be used
effectively, one needs to know
the breed averages, the
accuracy of the EPDs, and who
estimated the EPDs.
A high EPD is not necessarily
good; it depends on the trait
being considered and breeding
objectives.
Illustration of DNA
Double Helix from
Wikipedia.
Modern Genetics
In recent years, traditional
methods of improvement
through selection and breeding
have been superceded by
genetic manipulation.
A substantial amount of
research has focused on direct
manipulation of genes and DNA.
Illustration of DNA
Double Helix from
Wikipedia.
Gene Transfer
Genetic engineering basically
refers to transferring a gene
from one individual to another.
Illustration of DNA
Double Helix from
Wikipedia.
Scientists are able to code
genes for desirable compounds
and insert them into other cells,
such as microorganisms.
These microorganisms produce
these desirable compounds on
a large scale.
Illustration of DNA
Double Helix from
Wikipedia.
This area of genetic manipulation
makes important contributions to
domesticated animals in relation
to immunology, vaccines, aging,
and cancer.
“Annie the cow:
bioengineered to have
a gene for mastitis
resistance” (USDAARS).
Illustration of DNA
Double Helix from
Wikipedia.
Photo by Scott Bauer courtesy of USDA Agricultural Research Service.
The implications for introducing
superior production,
conformation, and diseaseresistant traits into domestic
animals through gene transfer
hold considerable promise in
the genetic improvement of
animals.
Illustration of DNA
Double Helix from
Wikipedia.
Cloning
Embryonic cloning of animals
involves the chemical or
surgical splitting of developing
embryos shortly after
fertilization and, consequently,
developing two identical
individuals.
Illustration of DNA
Double Helix from
Wikipedia.
The separated embryos are
allowed to culture, or grow, to
a more advanced embryonic
stage before they are
implanted into the uterus of a
recipient mother for full
development.
Illustration of DNA
Double Helix from
Wikipedia.
Embryonic cloning has been
performed successfully in
several species of animals.
Illustration of DNA
Double Helix from
Wikipedia.
Nuclear Transfer
Nuclear transfer is another
method of cloning that involves
the microsurgical collection of
nuclear material from a donor
cell which is then transferred
into an unfertilized ovum that
has had its own nucleus
removed.
Illustration of DNA
Double Helix from
Wikipedia.
The cells that develop successfully
become identical individuals.
Dolly the Sheep
(the first mammal
cloned from adult
cells) and many
other species
have been cloned
this way.
Illustration of DNA
Double Helix from
Wikipedia.
Photo courtesy of Wikipedia.
Worldwide, the institute that has
cloned the most species is Texas
A&M University, College of
Veterinary Medicine, which to
date has cloned cattle, swine, a
goat, a horse, deer, and a cat.
Illustration of DNA
Double Helix from
Wikipedia.
Nuclear Fusion
Another innovation in genetic
engineering, called nuclear
fusion, involves the union of
nuclei from two gametes,
male or female sex cells.
Illustration of DNA
Double Helix from
Wikipedia.
This fusion shows promise for
the uniting of nuclei from two
outstanding females, two
outstanding males, or the
normal outstanding male and
female combination.
Illustration of DNA
Double Helix from
Wikipedia.
The possibility for selecting
desired traits at the cellular
level holds exciting implications
for the genetic improvement of
domestic animals.
Illustration of DNA
Double Helix from
Wikipedia.
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Instructional Materials Service
Texas A&M University
2588 TAMUS
College Station, Texas 77843-2588
http://www-ims.tamu.edu
2006
Illustration of DNA
Double Helix from
Wikipedia.