Animal Genetics: Basics of Inheritance

• Animal genetics is the study of heredity and variation in animals

Basics of Inheritance

• Genes are the basic units of heredity
• Chromosomes are structures within cells that contain genes
• DNA (deoxyribonucleic acid) is the molecule that carries genetic information
• Genotype refers to the genetic makeup of an animal
• Phenotype refers to the observable characteristics of an animal
• Alleles are different forms of a gene
• Homozygous means having two identical alleles for a trait
• Heterozygous means having two different alleles for a trait
• Dominant alleles express their trait even when paired with a recessive allele
• Recessive alleles only express their trait when paired with another recessive allele
• Mendelian inheritance describes the basic patterns of inheritance

Chromosomes and Genes

• Animals typically have pairs of chromosomes, one set inherited from each parent
• The number of chromosomes varies among species
• Genes are located on chromosomes at specific locations called loci
• The complete set of genes in an animal is called its genome

DNA Structure and Function

• DNA consists of two strands forming a double helix
• Each strand comprises nucleotides
• Nucleotides include a sugar, a phosphate group, and a nitrogenous base
• The four nitrogenous bases are adenine (A), guanine (G), cytosine (C), and thymine (T)
• A pairs with T, and C pairs with G
• DNA replication is the process by which DNA copies itself
• DNA provides the instructions for protein synthesis
• Transcription is the process of creating RNA from DNA
• Translation is the process of creating proteins from RNA

Genetic Variation

• Mutation is a change in the DNA sequence
• Mutations can be spontaneous or induced by environmental factors
• Mutations can be harmful, beneficial, or neutral
• Genetic drift is the random change in allele frequencies in a population
• Gene flow is the movement of genes between populations
• Natural selection is the process by which animals with certain traits are more likely to survive and reproduce
• Genetic variation is the raw material for evolution

Quantitative Genetics

• Quantitative traits are traits that are measured on a continuous scale
• Examples of quantitative traits include weight, height, and milk production
• Quantitative traits are influenced by multiple genes and environmental factors
• Heritability is the proportion of phenotypic variation that is due to genetic variation
• Breeding value is the genetic merit of an animal for a particular trait
• Selection is the process of choosing animals with desirable traits to be parents
• Artificial selection is the intentional selection of animals by humans
• Natural selection is the selection that occurs in nature

Molecular Genetics

• Molecular genetics deals with the structure and function of genes at the molecular level
• Gene cloning is the process of making multiple copies of a gene
• Genetic engineering is the process of altering the genetic makeup of an animal
• Transgenic animals are animals that have had foreign genes inserted into their genome
• Gene editing technologies such as CRISPR-Cas9 allow for precise modification of DNA sequences
• Genomics is the study of the entire genome of an animal

Population Genetics

• Population genetics studies the genetic composition of populations
• A population is a group of animals of the same species that interbreed
• Gene pool is the total collection of genes in a population
• Allele frequency is the proportion of an allele in a population
• Hardy-Weinberg equilibrium describes the conditions under which allele and genotype frequencies remain constant in a population
• Factors that can disrupt Hardy-Weinberg equilibrium include mutation, gene flow, genetic drift, and selection
• Inbreeding is the mating of closely related animals
• Inbreeding can lead to an increase in homozygosity and a decrease in genetic variation
• Outbreeding is the mating of unrelated animals
• Outbreeding can lead to an increase in heterozygosity and an increase in genetic variation

Applied Animal Genetics

• Animal breeding is the application of genetics to improve livestock production
• Marker-assisted selection uses DNA markers to identify animals with desirable genes
• Genomic selection uses the entire genome to predict the breeding value of an animal
• Conservation genetics is the application of genetics to conserve endangered species
• Forensic genetics uses DNA to identify animals involved in crimes

Genetic Disorders

• Genetic disorders are diseases caused by mutations in genes
• Some genetic disorders are inherited in a simple Mendelian fashion
• Other genetic disorders are complex and influenced by multiple genes and environmental factors
• Genetic testing can be used to identify animals that carry genes for genetic disorders
• Genetic counseling can help breeders make informed decisions about breeding animals with genetic disorders

Epigenetics

• Epigenetics is the study of heritable changes in gene expression that do not involve changes to the DNA sequence itself
• Epigenetic modifications include DNA methylation and histone modification
• Epigenetic modifications can be influenced by environmental factors
• Epigenetics plays a role in development, disease, and evolution