vet-tech-therio-ch-4

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darlene.m.nelson
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105505
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vet-tech-therio-ch-4
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2011-09-30 21:21:53
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vet tech theriogenology chapter cytogenetics set
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vet tech theriogenology chapter 4 cytogenetics set
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  1. Cytogenetics
    study of the genetics of the cell/chromosomes
  2. Genome
    • total set of chromosomes in a cell
    • equal to the sex chromosomes plus the autosomes
    • have now mapped this for dogs as well as humans
  3. Chromosomes
    • can be examined under a normal light microscope
    • with proper preparation and staining, can see:
    • - number
    • - morphology
    • highly condensed chromosomes (when separating during mitosis/meiosis) are easy to see as they soak up a lot of stain
  4. Sex chromosome or Barr body
    • during interphase,
    • - may be able to identify one of the X chromosomes in a female
    • - one of the X chromosomes is elongated
    • - one of the X chromosomes contracts (denser, so picks up more stain), forms dot-like feature in the nucleus (Barr body)
    • - male X chromosome remains elongated, Y chromosome too small to see
    • - cells from dorsal ganglion of spinal cord work well
    • - cells lining the mouth (buccal smear) also work and are much easier to get
    • - cattle and sheep have keratinized (hardened) cells lining the mouth, so not possible to identify sex
  5. chromatin/Barr body from bucall smear
    • - use white blood cells
    • -- in nucleus of polymorphonucleocytes (multiple shaped nucleus, like neutrophil), contracted X chromosome forms a mass that looks like a chicken leg - drumstick appendage
    • method used to check genetic sex of males and female athletes in the 1950s and early 1960s
  6. Mitotic metaphase chromosomes
    • procedure to examine whole chromosome complement in a cell
    • 1. Peripheral blood sample (lymphocytes) or any dividing cell, eg skin cells
    • 2. cells are cultured - given proper nutrients and conditions for growth - to stimulate cell division
    • 3. some cells are removed from culture and treated to stop mitosis during metaphase
    • 4. dyes are added to make the chromosomes easy to see
    • 5. cell suspensions is dropped onto microscope slide, cell wall breaks, chromosomes spread out on the slide
    • 6. cells are inspected under a microscope. Chromosomes are sorted, examined from obvious abnormalities, and counted
  7. Karyotype
    • chromosomes are arranged in an internationally known order
    • number and structure of chromosomes in any given cell
    • each species has a characteristic karyotype
    • within any species, each sex has a characteristic karyotype
    • all chromosomes appear in pairs
    • in females, all pairs have the same size and shape
    • in males, all autosome pairs have the same size and shape, sex chromosomes differ
  8. Karotype - differences between species
    • size of chromosomes
    • shape of chromosomes
    • number of chromosomes
  9. Meiotic chromosomes
    • only ready source is really post-pubescent males
    • in females, meiosis takes place in the embryo, and is completed at ovulation for each ova
    • staining - characterizes small segments of each chromosome
    • - G-banding (Geisa) - produces barcode-like efect along the length of each chromosome; unique for each homologous pair
    • - chromosome paint - links a dye of stain to a specific piece of DNA; identifies abnormal vs normal
  10. Chromosomal abnormalities
    • normal number of chromosomes in an autosomal cell is diploid
    • chromosomes come in homologous pairs - one from mother, one from father
    • normal number of chromosomes in a germ cell is haploid
    • will only be passed to offspring if occurs in sperm or ova
  11. Numerical chromosomal abnormalities
    • heteroploidy
    • polyploid
    • triploidy
    • tetraploidy
    • aneuploid
    • monosomy
    • trisomy
  12. Heteroploidy
    any deviation from diploid number
  13. Polyploid
    • cells which have whole multiples of the haploid number of chromosomes above the diploid
    • eg cat with 57 (38 + 19)
    • triploidy is 3x haploid number (as cat example)
    • tetraploidy is 4x
  14. Aneuploid
    cells which have a few chromosomes more or less than the diploid number (more genetic material is better than less for the cell)
  15. Monosomy
    one of a homologous pair of chromosomes is missing
  16. Trisomy
    cell with an extra chromosome of a homologous pair, eg XXY male
  17. Structural chromosomal abnormalities
    • breakage of genetic material occurs frequently
    • normal repair mechanism work quickly to rectify the damage
    • - repaired chromosome is undamaged (functions as if nothing was ever wrong)
    • - sometimes repair cannot take place, eg when genetic material is lost
    • includes deletion and translocation
  18. Deletion
    • break in the chromosome that fails to repair
    • some genetic material is lost
    • lethal deletion - lost material contains a gene essential to life
    • non-lethal deletion - not lethal, but abnormality in animal may be seen (inhibits normal development)
    • if lost genetic material is not a coding gene (heterochromatin), there may be no effect at all
  19. Translocation
    • genetic material is not lost, but moved to a new place
    • within the same chromosome or on another chromosome
    • due to a mis-repair of a breakage within one or more chromosomes
    • does not alter the function of the animal carry the translocation because no genetic material is lost
    • pairing up during meiosis is compromised thus reducing fertility - degree of reduction depends on the type of translocation and the particular genetic material involved in the rearrangement
  20. Multiple cell lines
    abnormalities can occur in a single cell, any number of cells, all cells in the body
  21. Mixoploid
    some normal cells, some with chromosomal abnormalities
  22. Mosaic
    mixture of cells come from one original cell
  23. Chimera
    mixture of cells derives from two cell lines

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