Genetic Selection and Transfer

Compiled by: IMSStolen and edited by: Brandon Freel

Objectives

Investigate genetic selection methods.

Develop a logical argument for cloning.

Distinguish between embryonic cloning and nuclear transfer.

Genetic Selection

•Permanent improvements in domestic animals can be made by genetic selection through natural or artificial means.

•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.

Photo by Peggy Greb courtesy of USDA Agricultural Research Service.

Genetic Selection

•The goal of selection is to increase the number of animals with optimal levels of performance, while culling individuals with poorer performance.

•Genetic improvement is a slow process and can take several generations to see an improvement in a trait.

Genetic Selection

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)

Photo by Scott Bauer courtesy of USDA Agricultural Research Service.

Genetic Selection

•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.

Genetic Selection

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%

Heritability of Various Traits in Livestock

•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.

Genetic 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.

Genetic 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 Selection

•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).

Genetic Selection

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.

Genetic Selection

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.

Genetic Selection

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 basically refers to 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

This area of genetic manipulation makes important contributions to domesticated animals in relation to immunology, vaccines, aging, and cancer.

Photo by Scott Bauer courtesy of USDA Agricultural Research Service.

Gene Transfer

The implications for introducing superior production, conformation, and disease-resistant traits into domestic animals through gene transfer hold considerable promise in the genetic improvement of animals.

Gene Transfer

Cloning

Embryonic cloning of animals involves the chemical or surgical splitting of developing embryos shortly after fertilization and, consequently, developing two identical individuals.

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.

Cloning

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.

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.

Photo courtesy of Wikipedia.

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 Transfer

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.

Nuclear Transfer

The possibility for selecting desired traits at the cellular level holds exciting implications for the genetic improvement of domestic animals.

Nuclear Transfer

Objectives

Investigate genetic selection methods.

Develop a logical argument for cloning.

Distinguish between embryonic cloning and nuclear transfer.