Module 2

• Species


  A discrete, reproductively defined system of populations with a common evolution
• Population


  A group of animals of one species which interbreed
• Gene pool


  Set of genes and/or alleles in the entire population
• Breed


  A population distinguishable from another of the same species by frequencies of genes, chromosomal variation, or hereditary phenotypic characteristic
• Population genetics


  Allele frequencies of a population of animals
• Trait "fixed" within a species

  All the animals are homozygous for the same allele
• Hardy-Weinberg equilibrium


  • Gene frequencies remain stable if: Mating is random, No selection, No mutation, No migration, Large population (no drift)
• Assortative mating


  Both mates have the "same" trait, but this also means the two mates do not have the "same" trait - they are the same but different
• Natural selection


  Ability of certain individuals, with certain traits to survive and reproduce
• Artificial selection


  Choice of certain animals as breeding stock based on certain traits
• Fitness


  Ability to contribute to the gene pool of the next generation
• Effective population size


  The number of cows, or animals, needed to avoid inbreeding and maintain variation for selection (avoid fixation)
• Synders ratios


  Ratios used to determine the proportion of recessive or dominant offspring per parental mating type
• Genetic drift


  Small subpopulations become increasingly different over generations
• Founder effect


  The founding population is small, but the new population can be quite different from the parent population in terms of gene frequency
• Population bottleneck


  Population is severely reduced in numbers for one or more generations
• Gene flow


  Exchange of new alleles between subpopulations
• Panmictic populations


  Random mating in breeding population, there is an exchange of breeding animals - everyone has an equal chance of breeding with others
• Genetic isolates


  The subpopulation breeds only within itself, "closed" herd. Pretty isolated group from other populations gene flow - very closed system
• Cline


  Phenotypic gradients across a geographical region
• Migration


  Migration of wild animals could be from their own movement or in domestic animals could be from purchase, trucking to a new bar or ranch (by their owners)
• Gene flow, or migration, assures a constant source of genetic variation, retards random drift, and allows for the spread of a new negative OR positive mutation
• Selection


  In most domestic animals' selection is done by the owners/breeders. Selection against certain animals either means they are not bred at all, or a proportion are not bred
• Heritability


  Measure of the degree of which the offspring will resemble the parents for a specific trait you are looking at. An assessment of how successfully or quickly a trait can be improved by selection
• Heritability generalizations


  • High: Growth, length of hair in sheep, % bone in beef
  • Medium: Function, behaviour, average daily gain in beef, milkfat
  • Low: Fertility, stamina, pig litter size, sheep conception rate
• Goal of an animal breeder

  To change the phenotype, improve the environment, and change the genotype of breeding stock
• Interactive effects


  Two or more loci "interact" on one trait
• Epistasis


  The gene that is doing the masking of another gene
• Hypostasis


  The gene that is being masked
• Additive effects


  Multiple genes dictating a trait, the more of the "large" alleles the higher the expression of the trait
• Repeatability


  Measure of different variation within a gene. It is the correlation of several measurements from a single animal and how repeatable is that trait
• Microsatellite markers


  Used for parentage analysis as well as degree of relatedness
• Parentage verification


  Using microsatellite marker alleles to determine if a calf has one allele from the dam and one from the sire
• Parentage verification is NOT "proof of parentage" because many bulls carry the same allele number</b>
• Dogs, cats, sheep, goats, etc. can have more than one sire per litter
• Characteristics of genetic markers

  • Heritable, Present throughout lifetime, Simple lab method (=cheap), Polymorphic (more than one allele, but the more the better)
• Variants in non-coding sequences are advantageous because introns and non-coding DNA are more polymorphic than exons
• DNA sources include blood, semen, embryos, milk, and hair roots
• Parentage testing labs: Cattle- quantum genetix saskatoon and Neogen Edmonton. Horses: Mann equitest, Guelph. Dogs -healthGene Inc., Toronto
• DNA tests can be for other purposes as well such as breed identification. Your results depend on which markers were taken in the panel; different labs could give you different results