Genetics Constitution of Populations PDF

# Genetics Constitution of Populations ## What is the "best" animal? The purpose or aim of animal breeder: * There are two fundamental questions faced by animal breeders. * The first asks, what the "best" animal is? **For example, in dairy cattle** Is the best dairy cow: * The one that giv...

# Genetics Constitution of Populations ## What is the "best" animal? The purpose or aim of animal breeder: * There are two fundamental questions faced by animal breeders. * The first asks, what the "best" animal is? **For example, in dairy cattle** Is the best dairy cow: * The one that gives the most milk? * The one with the best feet, legs, and udder support? * Or, the one combine performance in these traits in some optimal way? The answers that breeders decide upon determine the **direction of genetic change** for breeding operations, breeds, and even species. ## What is genetics? Genetics is a science that studies heredity and variation. * **Heredity** is the transmission of traits from the parents to the offspring via genetic material. * **Variation** (refers to genetic variation) is the occurrence of differences among individuals of the same species. Therefore, **genetics in general concerns with:** * The genetic constitution of organisms, and * The laws governing the transmission of this hereditary information from one generation to the next. ## The science of genetics can be broadly divided into four major sub disciplines: 1. Transmission genetics (classical genetics) 2. Molecular genetics 3. Population genetics 4. Quantitative genetics ### Transmission Genetics Transmission genetics is primarily concerned with genetics processes that occur within individuals, and how genes are passed from one individual to another. * Thus, the unit of study for transmission genetics is the individual. ### Molecular genetics In molecular genetics, we are largely interested in the molecular nature of heredity: how genetic information is encoded within the DNA and how biochemical processes of the cell translate the genetic information into influencing the phenotype. * Consequently, in molecular genetics we focus on the cell. ### Population genetics Population genetics, the subject of this book, is the field of genetics that studies heredity in **groups of individuals for traits that are determined by one, or only a few genes**. ### Quantitative genetics Quantitative genetics, also the subject of this book, considers the heredity of traits in groups of individuals, but the traits of concern are determined by **many genes simultaneously**. ## A Mendelian population: Is a group of sexually reproducing organisms with a relatively close degree of genetic relationship (such as species, subspecies, breed, strain, etc.) residing within defined geographical boundaries where inbreeding occurs. * In animal breeding, we deal with the genetics of populations of individuals (**population genetics**). ## Extension of Mendelian Genetics Concerned with the distribution of genotypes resulting from a single progenies. * **Or** The classification of individuals (kind) * Introducing new concepts connected with the genetic properties of populations. * Introducing new concepts connected with the inheritance of measurements (degree). **Population genetics** **Quantitative genetics Or Biometrical genetics** ## How are animal populations improved genetically? The second question asks, how are animal populations improved genetically? This questions involves genetic principles and animal breeding technology. * The main purpose of animal breeder **is not** to genetically improve individual animals - once an individual is conceived, it is a bit late for that, but to improve animal populations, to improve future generations of animals. ## Genetic Structures of Populations An understanding of the genetic structure of a population is a key to out understanding of: * The importance of genetic resources, and * The importance of genes for the conservation of species and biodiversity. The genetic structure of a population is **determined** by the total of all alleles (the gene pool). * Thus the genetic structure (i.e. gene pool) is **described** in terms of calculating allelic frequencies and genotypic frequencies within the population.