ANSC 313

• Inheritance patterns


  • Single gene
  • Autosomal inheritance
  • Autosomal dominant
  • Co-dominant
  • Incomplete dominant
  • Autosomal recessive
• Ethical mate choice


  Both matings produce 50% manx kittens but in one, none are deformed and die
• This contradicts mating best to best
• Overo in horses


  OO lethal
• Manx tail in cats


  MM lethal
• Chinese crested dog


  • Hair missing on much of body
  • Tooth anomalies
  • Hairlessness is a homozygous lethal
  • pp= powder puff
  • Pp= show quality
  • PP= lethal
• Sometimes more than 2 alleles at a locus
• Melanocortin receptor 1 gene

  • E^D= black
  • e/e= red
• Melanocytes


  • Hair follicle and melanocyte
  • phaeomelanin= red, yellow, cream
  • eumelanin= black, brown, gray
  • E^+= wild type, color dependent on other genes
• Dominance hierarchy of alleles

  Some more dominant than others
• Autosomal dominant inheritance


  • Dominant, dominance hierarchy
  • Codominance
  • Incomplete dominance
  • Heterozygote can have a different phenotype than either homozygote
• Heterozygote phenotypes

  • Heterozygotes are different from either homozygotes
  • Codominant: both phenotype expressed together but observed separately
  • Incomplete dominant: both phenotypes expressed as a blended appearance
• Codominant


  • Merle colour in dogs, roan in cows
  • Red and white flower combined showing both colors
• Incomplete dominant


  • Palomino in horses
  • Red and white flower making pink flower
• Autosomal recessive generalizations


  • Most are enzyme deficiencies (inborn errors of metabolism)
  • Phenotype is generally consistent
  • Symptoms often severe
  • Consanguinity common: descend from same ancestor, related, inbred
  • Most enzymes deficiencies (inborn errors of metabolism)
  • Phenotype is usually consistent, especially within a family
  • Symptoms often severe: many disorders are present at birth, if untreated they are often lethal
  • Consanguinity common (relatedness, shared blood); such disorders show up when inbreeding or linebreeding is used
  • Cull the homozygote affected
  • Both carriers are obligate carriers then may cull or do not breed together
  • Variable expressivity: how much of the gene is shown, dimmer switch on light
  • Reduced penetrance: whether the gene shows or not, off/on switch
• Carrier detection tests


  • Breeding tests
  • Biochemical tests
  • DNA test for the mutation
• Most tests now based on PCR (method to amplify small amounts of DNA)
• DNA tests for diseases

  • Brown swiss cattle: weaver syndrome
  • braunvieh/brown swiss: albinism
  • Dexter cattle: dwarfism
  • Pigs: malignant hyperthermia
  • Goats: maple syrup urine disease
  • Horses: overo/lethal white foal syndrome, combine immunodeficiency
  • Sheep: spider syndrome
  • Dogs: von willebrand factor, black hair follicular dysplasia, cyclic neutropenia
• DNA tests for economic traits

  • Dairy cattle: leptin fat levels for grade in beef/milk yield, milk quality
  • Cattle: double muscling, gene star M marbling, (brahma; gene star T tenderness), mu-calpain beef tenderness, polled, red/black coat color, roan coloration, white heifer disease, cheese making (holstein), increase fat in milk (holstein), brown coat color
  • Horses: red/black coat color, recessive black coat color (agouti)
  • Pigs: red/black coat coloring, litter size, shite skin
  • Sheep: boorola fecundity, callipyge (double muscling)
  • Dogs: brown coat color, recessive black coat color, fawn/sable coat color
• Indirect tests

  DNA linkage tests
• DNA linkage tests


  • Used when the causative gene is not yet known
  • Location of gene, or biochemical pathway is known
  • Less accurate than direct tests, depends on distance of marker to gene
  • Use marked linked to causative gene
  • Dna variation within an intron or other noncoding segment
  • Markers do not affect any phenotype so have accumulated in animals must sample family to test for carriers because pedigree specific
  • Also used if dominant disorder is late onset, so that genotype is known prior to breeding
• Polycystic kidney disease

  Autosomal dominant, persian cats and breeds with persian, cysts develop by 12 months, renal failure later in life, premature stop codon in PKD1 gene
• Sex related inheritance patterns


  • Sex linked
  • X-inactivation
  • X-linked traits
  • X-linked diseases
  • Z-linked traits
  • Sex linked dominant
  • Y-linked=holandric
  • Sex-influence traits
• Scurs


  • begin growth at 4 months of age, not attached to the skull (wiggle horns)
  • Horned skull is flat
  • Scurred skull is curved
  • Polled skull is pointed
  • Gene on chromosomes 19, not identified yet
  • Bulls need only one copy to grow scurs, females need two
  • ScSc: cow and bull both scurred
  • Scsc: female smooth but bull scurred
  • Ssc: both smooth
• Epistasis


  genotype at one locus is able to mask the phenotype cause by the genotype at another locus
• If epistatic gene it does not allow any other alleles to show up phenotypically
• If homozygous polled PP they will always be polled
• If homozygous horned pp they will always be horned
• If heterozygous polled Pp the scurs may show
• Pp female


  • SCSC scurs
  • SCsc and scsc smooth
• Pp male

  • SCSC and SCsc scurs
  • scsc smooth
• All scurred cattle are Pp never PP
• All scurred demaes are ScSc cull
• Sex limited traits


  • Cryptorchidism; miniature breeds
  • Antlers only on males
• Pleiotropy


  disorder where multiple organ systems are affected
• Polled intersec goats

  PP female is intersex and polled is sterile
• Exceptions related to mendelian inheritance

  • Pleiotropy
  • Epistasis; scurs
  • Interdependence; brown color in cattle or dogs
• Types of chromosomes


  • Telocentric: no short arms
  • Acrocentric: tiny p arm
  • Submetacentric: p arm shorter than q arm
  • metacentric : arms of equal size
• To bring dna out of nucleus

  Need to bring cell to prophase then kill the cell break open the nucleus to release DNA and dye it
• Karyotyping


  • Arranged by size, descending order, numbered
  • Sex chromosomes last XY male mammal, ZW female bird
  • Short arm (p) up
  • Autosomes
  • Grouped by centromere placement