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2011-09-23 23:01:37
vet tech theriogenology chapter Mendelian Genetics set

vet tech theriogenology chapter 2 Mendelian Genetics set
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  1. Inheritance
    • the passage of genes from one generation to the next
    • the results are predictable (except for mutations)
  2. Mendelian genetics
    concerned with the action of a few genes causing discrete variation
  3. Discrete Variation
    • an animal either has the characteristic (trait) or not
    • eg poll gene = either horned or not horned
  4. Characteristics (traits)
    coded for by genes
  5. Genes
    • a segment (specific sequence) of bases in the DNA molecule
    • ~22000 genes in mammals (all mammals are about the same)
    • to some extent (in certain circles): allele (the how) = gene (the what) = locus (the where)
  6. Gene locus
    • place on the chromosome where the gene is located
    • each gene is always found at the same locus
    • different genes have different loci
    • no two genes have the same locus
    • every animal of the same species has the same gene at the same locus on the chromosome
  7. Chromosomes
    • come in pairs
    • homologous pairs - one from the mother and one from the father
    • 2 copies of each gene in a cell, one in each homologous chromosome
  8. Genes on the same chromosome
    • tend to be inherited together, eg white coat, blue eyes, deafness
    • can get separated during crossing over in meiosis
  9. Gene linkage
    • genes for certain traits are close together on the chromosome
    • are (almost) always inherited together (remember mutations)
    • does not mean the have the same function or interact with each other
  10. Sex-linked genes
    • genes that have their loci on the sex chromosomes
    • normal "housekeeping" genes that allow the cell to function
    • most have nothing to do with the determination of sex
    • most located on X chromosome
    • eg hemophilia, color blindness, red eyes in fruit flies, cat coat color (calico, torti)
  11. Sex-limited genes
    • located on the autosomes
    • refers to when the gene can be expressed - limited to one sex or the other
    • genes whose expression is limited depending on the sex of the animal
    • eg milk production genes carried in both male and female; only expressed in female
  12. Mutation
    • "mistake" in DNA replication
    • change in the sequence of bases in the DNA molecule
    • not all result in physical changes to organism (occurs in "rubbish"/non-functional DNA)
    • only results in physical changes if it occurs in the sequence of a gene
    • genetic change
    • responsible for all phenotypic variation (outward appearance)
    • if occurs in spermatogonium or oocyte, the changed gene will be passed to next generation
    • mutation produces an allele of the original gene
  13. Lethal mutation
    • vital gene is altered
    • can no longer code for its end product
    • new form of gene (lethal gene) is ineffective in future cells
  14. Lethal gene
    • new form of gene caused by mutation
    • can still code for product, but the end result is not the same as original
  15. Alleles
    • different forms of a segment of DNA that can exist at a particular site in a chromosome
    • alleles of a gene occupy same locus in the chromosome as original gene
    • some genes have no alleles
    • some genes have manu alleles
  16. Allelic series
    more than 2 allels exist in a population at a particular locus
  17. Homozygous
    2 copies of the same allele in a cell
  18. Heterozygous
    1 copy each of 2 different alleles in a cell
  19. Genetic fingerprinting
    • detects changes in base-pair sequences
    • uses these mistakes in non-coding ("rubbish") DNA as an individual characteristic to id an individual
    • variation in the repeat units creates a unique set of bands
  20. Dominant alleles
    • block the expression of other alleles in a series
    • will block the expressin of the recessive alleles
    • only need to be present on one of the pair of homologous chromosomes to be expressed
  21. Recessive alleles
    must be present on both homologous chromosomes before they can be expressed
  22. Co-dominant
    • 2 different alleles are present
    • both are expressed
    • eg blood types in humans
  23. Epistasis
    • Genes on different loci interact and affect each other
    • can cause gene penetrance
    • eg labrador retriever coat color
    • 1. B = black coat
    • 2. b = brown coat
    • 3. E = able to express dark coat - black, brown
    • 4. e = unable to express dark coat = yellow
  24. Incomplete gene penetrance
    • in a group of animals carrying a particular gene, only some exhibit trait or characteristic
    • expressed in some animals, but not others because...
    • 1. another gene on another locus is blocking the effect of the first gene (epistatic effect)
    • 2. genotype/environment (w/in animal or outside) blocks the expression of the gene so it cannot penetrate
  25. Variable expressivity
    • all animals carrying a gene express the trait, but to varying degrees
    • may be caused by polygenic, genotype/environment reaction, pleiotropism
  26. Polygenic
    • characteristic being governed by a number of genes
    • eg height, shoe size
  27. Genotype/environment interaction
    eg arctic fox, cats w/ points
  28. Pleiotropism
    • gene appears to affect more than one trait
    • may occur because:
    • 1. gene product is expressed at a number of different points
    • 2. one gene is acting, but genes are closely linked and are inherited together
  29. Gene nomenclature
    • 3 systems of nomenclature
    • 1 generally used is dominant alleles denoted by capital letter, recessive alleles by lower case
  30. Mendel's 1st law
    alleles separate to different gametes
  31. Mendel's 2nd law
    genes on non-homologous chromosomes undergo independent assortment