Genetic Selection and Transfer: Methods, Benefits, and Implications

1. Genetic Selection and Transfer Edited by: Jessica Hawley & Brandon Freel Compiled by: IMS

2. Objectives • Investigate genetic selection methods. • Develop a logical argument for cloning. • Distinguish between embryonic cloning and nuclear transfer.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. Heritability of Various Traits in Livestock

9. Polygenic Influence • Several genes influence some traits. • Ex. rate of growth is influenced by • appetite • energy expenditure • feed efficiency • body composition.

10. 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.

11. 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.

12. 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).

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. 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

20. 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.

21. 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.

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

23. Objectives • Investigate genetic selection methods. • Develop a logical argument for cloning. • Distinguish between embryonic cloning and nuclear transfer.