Genetics

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  • Genetics
    • Study of the science of heredity
      • Gregor Mendel 1800's
        • Mendel's 1st law - genes are passed on. Offspring - First Filial Generation
        • Mendel's 2nd law - if members of 1st filial generation are crossed with another then the resultant offspring will be in a 3:1 ratio dominant to recessive
    • Chromosomes
      • DNA molecules
      • 2 Identical Chromatids
      • Mammals - arranged in pairs. One from Mother and one from father
    • Genes
      • Site of gene on a chromosome = Locus
      • Code for a particular protein
    • Alleles / Allelomorphs
      • Different versions of a given gene
      • Dominant - suppress the effect of others
      • Reccessive -Alleles masked by the dominant version
    • Genotype
      • Heterozygous - 2 different alleles
      • Homozygous - two identical versions of a gene
    • Phenotype
      • Physical appearance
    • Back Crossing to the recessive
      • Homozygous animals will always breed true for a particular trait
      • Test the genotype
      • Reality - look back at stud books
      • Heterozygous X Homozygous. Progressive Retinal Atrophy inherited this way carried on Simple Autosome recessive gene - Dogs
    • Sex Linked genes
      • Y is little, so most sex linked characteristics found on X chromosome
        • Females tend to be carriers, Males tend to show condition
        • Tortoiseshell cats - orange colouration carried on X chromosome -> has to have 2 X chromosomes -> tend to be female
          • Can be male, not hermaphodite, must be chromosomally slightly abnormal - XXY or XXXY
    • Epistasis
      • Where a different gene altogether influences the expession of the alleles
    • Mutation
      • Rare occasions mistakes are made by the body whilst copying the DNA in gamete formation
        • Lethal Mutations - resultant gametes so altered that are inconsistent  with life, individual cannot survive
        • Some may not affect the new individual at all. Others convey an advantage - Evolutionary change
    • Inbreeding
      • Involves mating of individuals who are more closely related than animals chosen from general population
      • More likely to have many genes in common, increases likelihood of producing offspring with recessive traits
      • Less desirable traits may be passed along too.
      • Pedigree dogs - increased incidence of disease
    • Line Breeding
      • Form of inbreeding
      • Involves animals that are not so closely related
      • Mating within a certain family or line
      • Increases likelihood of obtaining desirable characteristics, without too high a risk of producing undesirable ones
    • Out-breeding
      • Breeding of individuals less closely related than mates chosen at random in the population
      • Increases heterozygousity and introduces new genes into the population
      • Heterosis/Hybrid vigour - this cross conveys this, conveys some superiority on the heterozygote
    • Deformities/Malformations
      • Deviation from normal anatomy
      • Foetal development or acquired during life
    • Congenital Abnormalities
      • Abnormality present from birth
      • May be inherited from parents through the genes or may be due to environmental factors which may result in failure of normal foetal development e.g. radiation or viral infections
        • Teratogen - Agent that induces a birth defect
    • Hereditary defects
      • Caused by genes inherited from parents
      • May not be apparent at birth - PRA

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