Transcript GeneticSelection

Edited by: Jessica Hawley & Brandon
Freel
Compiled by: IMS
• Investigate genetic selection methods.
• Develop a logical argument for cloning.
• Distinguish between embryonic cloning and
nuclear transfer.
Genetic Selection
• Two type of selection
• Natural selection-occurs in in the wild
• Artificial selection-planned and controlled by
humans.
• Permanent improvements in domestic animals
can be made by genetic selection through
natural or artificial means.
Genetic Selection
• The goal of selection:
• increase optimal levels of performance
• cull individuals with poor performance.
• Genetic improvement is a slow process
• can take several generations to see an
improvement in a trait.
Artificial Selection
• 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.
• Artificial insemination and embryo transfer are
breeding methods that are commonly used to
decrease the time taken to improve a trait.
Photo by Peggy Greb courtesy of USDA Agricultural Research Service.
Artificial Selection
• Artificial insemination- taking semen from a
male and breeding a female by artificial
means
• Embryo transfer- the act of taking an
embryo from one female and placing it
inside another female to carry to full term
“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)
Photo by Scott Bauer courtesy of USDA Agricultural Research Service.
Heritability
• Traits are passed from parents to offspring
• Some traits are more heritable than other
traits.
• Genotype’s of an individual will be expressed
more strongly and environment will be less
influential for particular traits.
Heritability of Various Traits in Livestock
Trait
Sheep Swine Cattle
Weaning weight
15-25% 15-20% 15-27%
Post-weaning gain
efficiency
20-30% 20-30% 40-50%
Post-weaning rate of gain 50-60% 25-30% 50-55%
Feed efficiency
50%
12%
44%
Loin eye area
53%
53%
56%
Polygenic Influence
• Several genes influence
some traits.
• Ex. rate of growth is
influenced by
•
•
•
•
appetite
energy expenditure
feed efficiency
body composition.
Trait Selection
• 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.
Trait Selection
• 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.
Genetic Merit
• 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).
Epd’s
• 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.
Epd’s
• 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.
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.
Gene Transfer
• Genetic engineering is transferring a gene
from one individual to another.
• 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.
Gene Transfer
• Genetic Engineering makes important
contributions to immunology, vaccines,
aging, and cancer.
• Introducing superior production,
conformation, and disease-resistant traits
into domestic animals through gene
transfer hold considerable promise in the
genetic improvement of animals.
• Dolly the Sheep
Photo by Scott Bauer courtesy of USDA Agricultural Research Service.
Cloning
• Two types of cloning; Embryonic and
Nuclear Transfer
• Embryonic cloning involves splitting
developing embryos shortly after
fertilization and developing two identical
individuals.
• The separated embryos grow to an
advanced embryonic stage before they are
implanted into the uterus of a recipient
mother for full development.
Nuclear Transfer
• Nuclear transfer 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.
• The cells that develop successfully become
identical individuals.
• Dolly the Sheep
Nuclear Transfer
• 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.
Nuclear Fusion
• Another innovation in genetic engineering,
called nuclear fusion, involves the union of
nuclei from two gametes, male or female sex
cells.
• This fusion shows promise for the uniting of
nuclei from two outstanding females, two
outstanding males, or the normal
outstanding male and female combination.
Genetic Selection
• The possibility for selecting desired traits at
the cellular level holds exciting implications
for the genetic improvement of domestic
animals.
• Investigate genetic selection methods.
• Develop a logical argument for cloning.
• Distinguish between embryonic cloning and
nuclear transfer.