BIO 402 — Principles of Plant and Animal Breeding: Lecture Note

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BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: BIO 402 Course title: Principles of Plant and Animal Breeding Course credit load: 2 Units Series 1: Foundations of Plant and Animal Breeding • Part 1.1: Introduction to Plant and Animal Breeding o Sub Part 1.1.1: Definition, scope, and history of plant and animal breeding o Sub Part 1.1.2: Objectives and importance of breeding programmes o Sub Part 1.1.3: Genetic basis of breeding: variation, heredity, and selection • Part 1.2: Importance of Plant Breeding o Sub Part 1.2.1: Crop improvement and food security in Nigeria o Sub Part 1.2.2: Development of improved crop varieties o Sub Part 1.2.3: Roles of plant breeding institutions in Nigeria • Part 1.3: Importance of Animal Breeding o Sub Part 1.3.1: Livestock improvement and productivity o Sub Part 1.3.2: Development of improved livestock breeds in Nigeria o Sub Part 1.3.3: Roles of animal breeding institutions in Nigeria • Part 1.4: Principles of Selection and Improvement o Sub Part 1.4.1: Types of selection: natural and artificial o Sub Part 1.4.2: Heritability and selection response o Sub Part 1.4.3: Genetic gain and the breeder’s equation

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Introduction Plant and animal breeding is the science of improving the genetic composition of plants and animals to enhance their value to human society. Through deliberate selection, crossing, and evaluation over successive generations, breeders develop varieties and breeds with higher yield, better quality, disease resistance, adaptation to local environments, and other desirable traits. The principles underlying these practices draw on genetics, statistics, physiology, and agronomy, making breeding one of the most applied and consequential biological sciences. Nigeria’s agricultural economy depends critically on both crop and livestock production; breeding improvements have historically delivered some of the largest productivity gains in Nigerian agriculture, from the high-yielding maize and cassava varieties developed by IITA to the trypanotolerant N’Dama cattle maintained in the forest zone. This Series introduces the definition, history, objectives, and genetic foundations of plant and animal breeding, surveys the importance of breeding for Nigerian food security and livestock productivity, and introduces the principles of selection, heritability, and genetic gain that underpin all breeding programmes. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1 define plant and animal breeding, describe their historical development, and state the objectives of breeding programmes (Linked to Part 1.1), • SLO 1.2 explain the genetic basis of breeding including the roles of variation, heredity, and selection (Linked to Part 1.1), • SLO 1.3 describe the importance of plant breeding for crop improvement and food security in Nigeria and name the principal plant breeding institutions (Linked to Part 1.2), • SLO 1.4 describe the importance of animal breeding for livestock improvement in Nigeria and name the principal animal breeding institutions (Linked to Part 1.3), • SLO 1.5 distinguish between natural and artificial selection and explain how each operates in breeding practice (Linked to Part 1.4), and

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS • SLO 1.6 define heritability, explain the breeder’s equation, and calculate expected genetic gain from selection (Linked to Part 1.4). 1.1 Introduction to Plant and Animal Breeding 1.1.1 Definition, scope, and history of plant and animal breeding Plant breeding is the science and art of changing the genetic constitution of plants to produce varieties better suited to human needs. It encompasses all methods of creating, selecting, and evaluating genetic variation in crop plants, from traditional farmer selection to modern molecular breeding and genetic modification. Animal breeding is the analogous science applied to domesticated animals; it uses knowledge of genetics and statistics to design mating systems that improve the frequency of desirable alleles in a population over successive generations. Both disciplines share the same genetic principles but differ in the biology of their subjects: plants may be self-pollinated or cross-pollinated, diploid or polyploid; animals are predominantly cross-fertilising diploids with longer generation intervals. Domestication of crop plants began approximately 10,000 to 12,000 years ago in multiple centres of origin including the Fertile Crescent (wheat, barley), East Asia (rice, soybean), Mesoamerica (maize, bean, squash), and sub-Saharan Africa (sorghum, pearl millet, yam, cowpea). Early farmers selected plants with non-shattering seed heads, larger seeds, and more palatable fruits over centuries of unconscious selection. Scientific plant breeding began in the late nineteenth century with the rediscovery of Mendel’s laws (1900) and was transformed by the development of hybrid maize in the 1920s to 1930s (Shull, East, Jones) and the Green Revolution high-yielding wheat and rice varieties of the 1960s (Borlaug, Chandler). Animal domestication began similarly; scientific animal breeding developed with the quantitative genetic theories of Fisher (1918) and Lush (1940s). Fill in the blank: The rediscovery of Mendel’s laws of inheritance in ________ provided the scientific foundation for systematic plant and animal breeding, explaining how discrete heritable factors (genes) segregate and recombine across generations.

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.1.2 Objectives and importance of breeding programmes The primary objectives of a breeding programme depend on the crop or species and the target environment, but commonly include: increasing yield per unit area or per animal; improving product quality (nutritional composition, processing quality, palatability); enhancing resistance or tolerance to biotic stresses (pests and diseases) and abiotic stresses (drought, heat, waterlogging, soil acidity); adapting varieties or breeds to specific agro-ecological zones; shortening the growth cycle or generation interval; improving harvest index or feed conversion efficiency; and maintaining or improving genetic diversity as insurance against new stresses. The importance of achieving these objectives is greatest in developing countries where food insecurity is acute and where smallholder farmers depend on crop and livestock performance for their livelihoods. In Nigeria, the development of early-maturing drought-tolerant maize varieties by IITA has allowed rain-fed maize cultivation in drier Guinea savanna areas previously considered unsuitable; trypanotolerant cattle breeds (N’Dama, West African Shorthorn) allow livestock production in tsetse-infested forest and forest-savanna mosaic zones where exotic zebu breeds cannot survive. Without breeding improvement, the productivity gains required to feed Nigeria’s rapidly growing population (estimated to exceed 400 million by 2050) would be impossible to achieve. Fill in the blank: A breeding programme designed to improve ________ tolerance in maize allows cultivation in drier areas of the Guinea savanna where unpredictable rainfall would otherwise cause crop failure, directly improving food security for smallholder farmers. 1.1.3 Genetic basis of breeding: variation, heredity, and selection All breeding depends on genetic variation: differences in allele frequencies among individuals in a population. Without variation, selection cannot change the genetic composition of a population across generations. Genetic variation arises from mutation (the ultimate source of new alleles), recombination during meiosis (which creates new combinations of alleles on chromosomes), and gene flow between populations. In breeding practice, variation is introduced or maintained by: crossing genetically diverse parents; using wild relatives or landraces as sources of novel alleles;

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS inducing mutation with physical or chemical mutagens; and, in modern breeding, transferring genes through transformation or genome editing. Heredity is the transmission of genetic information from parent to offspring. Mendelian heredity governs discrete (qualitative) traits controlled by one or a few genes with large individual effects; quantitative heredity governs continuous (metric) traits such as yield, body weight, and milk production that are controlled by many genes each of small effect (polygenes) and strongly influenced by environment. Breeding for quantitative traits requires statistical methods (quantitative genetics) to separate genetic from environmental effects and to predict the response to selection. Selection is the differential survival and reproduction of genotypes; artificial selection by the breeder replaces or supplements natural selection to increase the frequency of alleles that improve the target traits. Fill in the blank: Traits controlled by many genes each of small effect, such as grain yield and body weight, are called ________ traits; breeding improvement of these traits requires statistical quantitative genetics methods to separate genetic from environmental sources of variation. Pilot questions 1.1 1. Define plant breeding and animal breeding and state three objectives common to both. 2. Describe the historical development of scientific plant breeding from the rediscovery of Mendel’s laws to the Green Revolution. 3. Distinguish between qualitative and quantitative traits and explain why different genetic approaches are needed for each. 4. Explain the three sources of genetic variation that a breeder can exploit and state how each arises. 5. Why is genetic variation a prerequisite for any breeding programme? What would happen if a population had no genetic variation? 1.2 Importance of Plant Breeding 1.2.1 Crop improvement and food security in Nigeria Nigeria is the most populous country in Africa and faces an ongoing food security challenge driven by population growth, climate variability, post-harvest losses, and historically low

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS agricultural productivity. Plant breeding has made,

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