AS 251: Principles of Animal Breeding Study Notes
AS 251: Principles of Animal Breeding
Course Team
Prof. Kwaku Adomako
Dr. Bismark Kyei
Key Quote
C. Darwin: “We cannot suppose that all the breeds were suddenly produced as perfect and as useful as we see them now; indeed, in several cases, we know that this has not been their history. The key is man's power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him. In this sense, he may be said to make for himself useful breeds.” On the Origin of Species (1859, p. 30)
Course Outline
The Role of Breeding in Agriculture:
Breeding and related disciplines.
Skills required of a breeder.
Modes of reproduction in relation to animal and plant breeding.
Animal Genetic Resources conservation and utilization.
The Basics of Inheritance:
Monohybrid inheritance.
Dihybrid inheritance.
Trihybrid inheritance.
Polygenic inheritance.
Gene Interactions:
Allelic and non-allelic interactions.
Additive and non-additive gene action.
Sex-Related Inheritance:
Sex-linked inheritance.
Sex-influenced inheritance.
Sex-limited traits.
Phenotypic Variations in Farm Animals:
Expressivity, Penetrance.
Modifying genes.
Quantitative and qualitative traits.
Causes of phenotypic variation in farm animals.
Heritability
Principles of Selection:
Natural and artificial selection.
Selection for different kinds of gene action.
Selection for quantitative traits:
Mass selection, Pedigree selection, Progeny testing, Family selection (within family selection, between family selection, and sib selection).
Selection for more than one trait (Tandem selection, Independent culling levels, Index method).
Genetic Improvement:
Selection differential, Genetic progress.
Factors affecting genetic progress.
Mating Systems:
Inbreeding, inbreeding coefficient.
Outbreeding (Crossbreeding, Outcrossing).
The Origin of Animal Breeding
Recommended Textbooks
Animal Breeding and Genetics for BSc Students (2014) by Kor Oldenbroek and Liesbeth van der Waaij.
An Introduction to Practical Animal Breeding by Dalton, D. C. (1980).
Dalton’s Introduction to Practical Animal Breeding (4th Edition) by Willis, M. B. (1998).
Assignment
Describe genetically modified organisms in detail and discuss the merits and demerits of this genetic advancement.
Definitions of Some Animal Breeding Terms
Genetics: The science of heredity concerned with the behavior of genes passed from parents to offspring in the reproductive process. It is a branch of biology that focuses on heredity and variation, studying cells, individuals, offspring, and populations.
Gene: The functional unit of heredity; the smallest unit of inheritance determining heredity.
Trait: Any observable or measurable characteristic of an animal.
Alleles: Different forms of one type of gene (e.g. F or f).
Heredity: The transmission of traits from parents to offspring via genetic material.
Variation: The occurrence of differences among individuals of the same species.
Phenotype: The observable expression of a gene (e.g. eye color, height).
Genotype: The genetic makeup of an individual or a trait (e.g. BB for brown eyes).
Homozygotes: Genotypes with identical alleles (e.g. FF or ff).
Heterozygotes: Genotypes with unidentical alleles (e.g. Ff).
Population: A group of interbreeding individuals.
Epistatic Gene: A gene that suppresses or masks the phenotypic expression of another gene at another locus.
Hypostatic Gene: The gene that is suppressed by an epistatic gene.
Introduction to Animal Breeding
Animal Breeding involves the application of genetic principles for the improvement of economically important characteristics or traits in farm animals.
Breeding and Its Related Discipline
Genetics: Understanding inheritance and genes responsible for desired traits.
Molecular Biology: Involves genetic markers, genome mapping, and gene editing.
Biotechnology: Involves techniques like genetic engineering, tissue culture, and marker-assisted selection.
Animal Physiology: Understanding how traits are expressed and influenced by environmental factors.
Animal Science: Ensure practical application of breeding efforts to optimize productivity and sustainability.
Bioinformatics:
The Role of Breeding in Agriculture
Breeding plays a crucial role in agriculture by improving animals to meet human needs:
Improve yield.
Enhance quality.
Disease and pest resistance.
Climate adaptation.
Shortening growth cycles.
Improving input efficiency.
Preserving genetic diversity.
Economic benefits.
Modes of Reproduction in Relation to Animal Breeding
Natural Reproduction
Advantages:
Low cost and minimal technology.
Maintains genetic diversity in a population.
Disadvantages:
Limited control over genetic traits.
Risk of transmitting undesirable traits or diseases.
Assisted Reproductive Techniques (ARTs):
Artificial Insemination (AI): Sperm from a selected male is collected and artificially introduced into the female reproductive tract.
Embryo Transfer (ET): Fertilized embryos from a donor female (with superior traits) are transferred to a surrogate female.
In Vitro Fertilization (IVF): Eggs and sperm are combined outside the body to create embryos, which are then implanted in a female.
Cloning: Producing a genetically identical copy of an animal using somatic cells.
Sex-Sorted Semen: Sperm is sorted to produce offspring of a desired sex.
Cryopreservation: Freezing and storing gametes (sperm or eggs) or embryos for future use.
Hybridization: Crossbreeding animals of different breeds or species to combine desirable traits.
Application: Improving productivity, disease resistance, or adaptability.
Animal Genetic Resources Conservation and Utilization
Refers to the preservation and sustainable use of genetic material from animals. Critical for:
Food security.
Biodiversity.
Adaptability to environmental changes.
Resistance to pests and diseases.
Economic benefits.
Cultural and heritage value.
Skills Required of an Animal Breeder
Animal handling.
Knowledge in animal genetics.
Veterinary knowledge.
Record keeping.
Observation skills.
Husbandry skills.
Marketing and sales.
Animal nutrition.
Reproductive physiology.
Gene Interaction
Gene interactions: Phenomenon of two or more genes affecting the expression of each other.
Types of Gene Interaction:
Allelic Interaction:
Complete dominance.
Incomplete dominance.
Co-dominance.
Multiple alleles.
Non-allelic Interaction:
Additive gene interaction.
Duplicate gene.
Dominant suppression.
Dominant epistasis.
Recessive epistasis.
Allelic Interaction
Complete Dominance: The dominant allele fully masks the recessive allele.
Incomplete Dominance: The heterozygote expresses an intermediate phenotype.
Co-Dominance: Both alleles are fully expressed in the heterozygote.
Multiple Alleles: More than two alleles exist for a single gene, but only two are present in an individual.
Non-Allelic Interaction
Complementary Gene Interaction: Two genes work together to produce a phenotype, both required.
Supplementary Gene Interaction: One gene produces a phenotype; another gene modifies it.
Duplicate Gene Interaction: Two genes perform the same function; either dominant allele produces the phenotype.
Polygenic Inheritance: A trait controlled by multiple genes, each contributing a small effect.
Pleiotropy: A single gene affects multiple phenotypic traits.
The Basics of Inheritance
Monohybrid: A pair of genes.
Dihybrid: Two pairs of genes.
Trihybrid: Three pairs of genes.
Polygenic: Many genes (more than three pairs).
Monohybrid Inheritance
Examines the inheritance of a single gene with two alleles (dominant and recessive).
This can be illustrated using gene pairs:
Coat color in cattle (B, b)
Naked neck in chickens (Na, na)
Six possible inheritance crosses:
Homozygous dominant x Homozygous dominant: All offspring are homozygous dominant.
Example: P: NaNa x NaNa, BB x BB → F1: NaNa BB
Homozygous Dominant x Heterozygote: Half homozygous dominant, half heterozygous.
F1: NaNa, Nana → BB, Bb
Homozygous Dominant x Homozygous Recessive: All heterozygous.
F1: NaNa x nana → BB x bb → Nana Bb
Heterozygote x Heterozygote: A quarter homozygous dominant, half heterozygous, a quarter homozygous recessive.
P: Nana x Nana, Bb x Bb → F1: NaNa, 2Nana, nana → BB, 2Bb, bb
Heterozygote x Homozygous Recessive: Half heterozygous, half homozygous recessive.
F1: Nana x nana → Bb x bb → Nana, nana → Bb, bb
Homozygous Recessive x Homozygous Recessive: All homozygous recessive.
P: nana x nana → bb x bb → F1: nana bb
Dihybrid Inheritance
Involves inheritance of two pairs of genes (non-linked).
Illustrates four phenotypes from a cross:
Example: Black (B) and red (b) coat color genes; polled (P) and horned (p) genes.
Cross: BbPp x BbPp.
Dihybrid Cross Results
Gametes (Male & Female): BF, Bp, bF, bp
Phenotypic Ratio: 9:3:3:1 (9 Black polled, 3 Black horned, 3 red polled, 1 red horned).
Minimum of 16 individuals needed for all classes in correct proportions.
Trihybrid Inheritance
A mating between triple homozygous dominant and triple homozygous recessive produces triple heterozygotes.
Inter se mating of two triple heterozygotes yields a phenotypic ratio of 27:9:9:9:3:3:3:1.
Population size: 64; genotypes = 27; phenotypes = 8.
Polygenic Inheritance
Shows how traits are controlled by multiple genes:
Table of genotype and phenotype numbers produced for various gene pairs.
Sex-Related Inheritance
Sex-linked Inheritance: Transmission of traits located on sex chromosomes.
Types include: X-Linked and Y-Linked Inheritance.
X-Linked Inheritance
Traits determined by genes located on the X chromosome.
Examples: Certain diseases and conditions like hemophilia that are carried on the X chromosome.
Applications in Animal Breeding
Utilizes both natural and artificial selection.
A Boon for Genetic Improvement.
Negative Effects of Animal Breeding
Selective breeding can simultaneously impair other performance aspects.
Issues include fertility reduction and birthing difficulties.
Conclusion
The study of genetics and inheritance is vital for improving animal breeds, ensuring sustainability, and understanding the impact of breeding practices on health and performance.