Module 1

• Animal domestication


  The process of adapting wild plants or animals to live in association with humans
• Production requirements for animal domestication

  • Feeding and proper nutrition
  • Animal health
  • Specific selection of stock
• Domestication began


  10,000 – 20,000 BCE
• Selective breeding


  Specific for improving growth, performance or any trait that is selected to improve genetic value and choose those who have the desired phenotype
• Preventative medicine


  Includes culling decisions and dealing with genetic diseases
• Genetic diseases are usually untreatable, so it is usually best to cull the affected animal from breeding stock
• Herd genetics


  Can be determined through a variety of mating systems and selection methods and techniques
• Purebred breeders


  Most likely to seek genetic advice because their main products for sale are the genes
• The majority of genetic progress is done by purebred breeders or seed stock suppliers
• Genetic traits and diseases

  Could be acquired in the following ways: Congenital, Familial, Inherited
• Patterns of inheritance


  • Single gene
  • Chromosomal
  • Multifactorial
• Teratogens are environmental or outside factors that influence the growth or traits of an individual and has nothing to do with the actual genetics
• Family history


  Very important when looking at genetics, including factors such as age of parents, number of offspring and their sex, miscarriages or stillbirths or their breed
• Autosomal

  Trait is passed on a gene that is NOT a sex chromosome
• Autosomal dominant generalizations


  • Most are non enzyme protein disorders
  • Could have variable expressivity
  • Could have reduced or incomplete penetrance
  • Many are the result of a new mutation
  • Homozygote recessive is often lethal
• Variable expressivity


  The degree to which a phenotypic trait can be seen
• Reduced penetrance


  Either the presence or absence of a trait, where not all individuals with the allele express the phenotype
• Many autosomal dominant traits are the results of new mutations within a species
• Homozygous individuals for autosomal dominant traits usually results in early death
• Dominance hierarchy


  The ordered patterns of dominance
• Melanocortin Receptor 1 gene (MC1R)


  The gene that influences pigmentation
• Melanocyte components


  • Nucleus
  • Mitochondrion
  • Rough ER
  • Golgi apparatus
  • Melanosomes
• Phaeomelanin


  Responsible for producing red, yellow and cream pigments
• Eumelanin


  Responsible for producing black, brown and gray pigments
• Autosomal dominant inheritance


  Could be by codominance or incomplete dominance, where heterozygotes have a different phenotype than either homozygote
• Codominance


  • Merle colouring in Australian Shepherds
• Incomplete dominance


  • Palomino colour in horses
• Autosomal recessive generalizations


  • Most are enzyme deficiencies
  • Phenotypes are presented consistently
  • Symptoms are usually severe
  • Usually passed down through generations
• Enzyme deficiencies


  Arise from the inborn consequences of metabolism failure, often due to the build up of proteins that the lysosomes are unable to break down
• If the phenotype is expressed by autosomal recessive inheritance, then the trait is usually consistent within families
• Autosomal recessive diseases are usually severe, present at birth, and lethal if left untreated
• Consanguinity


  The state where traits are passed on and present throughout generations due to inbreeding
• The implication of autosomal recessive inheritance is to cull the affected individuals, as both parents are 'obligate' carriers with a 0% chance of unaffected offspring
• Carrier detection tests


  Typically performed on parents who are carriers to see what the chances of affected offspring are
• Breeding tests


  Involve mating a sire to an affected or heterozygous dam to see if affected offspring are born, to determine if the sire is a carrier
• Direct tests


  Could be biochemical (testing proteins and enzymes) or DNA (PCR tests looking for mutations)
• Indirect tests


  DNA linkage tests used when the causative gene is not known, to find a marker linked to the suspected gene
• Sex linked inheritance


  Occurs when the gene is on the sex chromosome, with fewer genes
• X inactivation


  Occurs in female mammals, where one of the X chromosomes is inactivated
• X linked diseases


  • Muscular dystrophy in dogs, hemophilia in horses and dogs