vet-tech-therio-ch-5

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darlene.m.nelson
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107590
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vet-tech-therio-ch-5
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2011-10-09 19:08:12
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vet tech theriogenology chapter sex chromosomes differentiation set
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vet tech theriogenology chapter 5 sex chromosomes and sex differentiation set
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  1. Sex chromosome
    X and Y chromosomes
  2. Male
    • XY
    • Y chromosome carries male-determining genes
  3. Female
    • XX
    • female is the "default sex"
    • "she" develops in the absence of the male-determining gene
    • male development must be triggered (they cause more work)
  4. X chromosomes
    • carry a number of genes
    • most of them are not involved with sex determination, involved with everyday life of the cell - "housekeeping genes"
    • there are more housekeeping genes than sex determination
    • larger in size - due to heterochromatin ("rubbish", non-coding genes)
  5. Y chromosomes
    • contain few genes that are not involved in sex determination
    • contains more sex deterimination genes than X chromosome
    • smaller in size - very little heterochromatin
  6. Gene Dosage Compensation Theory
    • aka the Lyon Hypothesis of X inactvation
    • the X chromosome is larger, carries more genes than the Y...
    • the XY complement is deficient in the "dose" of genes inherited from female, but ...
    • in the female, one chromosome becomes highly condensed, inactivated, but...
    • is facultative heterochromatin
  7. Facultative heterochromatin
    has the facility to return to active chromatin when/if needed
  8. Fertilization, early embryonic development
    • both X chromosomes are active, functional
    • one X chromosome ceases to function...
    • ...random as to which one is picked for each cell in existence at that point
    • cell nucleus multiplies and cell divides
    • - same X chromosome remains inactive in both daughter cells
    • "housekeeping" genes on X chromosome (also found on X chromosome) are not inactivated
  9. Pseudoautosomal region
    • part of sex chromosomes that pair up durng meiosis
    • prevents crossing over of sex-determining genes during meiosis
  10. Sex differentiation in the male
    • starts early in the embryo
    • in mammals, Y chromosome carries the primary male-determining genes
    • main gene - testis-determining gene (Tdy) aka sex-determining region (SRY)
    • controls expression of other genes (both on Y chromosome and some autosomes)
    • effect of expression of Tdy gene is that undifferentiated gonad develops as a testis
    • - XY embryo
    • -- undifferentiated gonad support cells (not gonad cells) direct goads to differentiate into a testis
    • - meiotic inhibition substance is secreted
    • - germ cells do not undergo meiotic division in the embryo once testis have differentiated
    • - Sertoli cells produce a Mullerian Inhibition Substance (MIS)
    • -- blocks the development of the Mullerian duct system (female reproductive system)
    • Leydig cells secrete testosterone
    • - stimulates the Wolffian duct system (male reproductive duct system)
    • at puberty, a spermatogenesis gene on the X chromosome of spermatogonia starts spermatogenesis by stimulating meiotic division
    • - sperm development starts at puberty
  11. Sex differentiation in the female
    • development happens by default - because male development is not directed, female development occurs
    • - XX embryo
    • -- no suppression of meiosis
    • -- germ cells in the undifferentiated gonads begin meiosis
    • -- cells orient themselves into the morphology of an ovary with a medulla and a cortex
    • -- oogonia do not complete the full meiotic process
    • --- remain resting at diplotene until just before ovulation in the post pubertal animal
    • -- female has all the eggs (not yet fully developed) she will ever have at birth
    • -- in the absence of suppression, the Mullerian ducts develop and the female duct system is established
  12. Embryo
    • gonadal sex is undifferentiated in the early embryo
    • although it is determined at fertilization, sex is not distinguishable until developed enough
    • - 30 days of gestation in the dog
    • - 40 days in the cat
    • because of embryonic similarities during development, homologies of genital organs in the male and female mammal exist
    • - see slide 11 or book for chart
  13. Tortoiseshell cats
    • coat color - mix of orange (aka ginger) and black or tabby
    • may have patches of white fur (piebalding)
    • white gene is on a separate autosome
    • color arises because:
    • - it is sex-linked
    • - it is epistatic to the autosomal black or tabby genes
    • female cats (tortis) are heterozygous for the orange gene
    • - one X chromosome has the orange gene and one does not
    • - only one X chromosome is functional in each cell
    • - functional X chromosome w/ orange gene
    • -- suppresses the black or tabby gene
    • -- only orange hair will be produced
    • - functional X chromosome without orange gene
    • -- black or tabby gene, whichever is present, will be expressed
    • - inactivation of X chromosome doesn't take place until ~ day 12 of embryogenesis in cats
    • -- result is patches of orange or patches of tabby or black
    • -- due to same active X chromosome in patches of cells
  14. Calico cats
    Sheila has never seen one w/o white (w/o piebalding)
  15. Male tortoiseshell cats
    • 1 in 3000 tortis are male
    • only 1 in 10,000 are fertile
    • chromosomally abnormal
    • - sex chromosome complement
    • -- XXY - Kleinfelter Syndrome
    • -- 2 distinct cell lines
    • --- eg XX/XY, XX/XXY, XY/XXY
    • -- must have at least one cell line with a Y chromosome
    • -- most are infertile (XXY - Kleinfelter)
    • -- those with a normal male cell line (XY) may be fertile
  16. XX/XY
    two cell lines - chimera
  17. XXY
    • single cell line
    • every cell has an extra X chromosome
  18. XX/XYY
    • two cell lines
    • one a normal female line, one trisomic
    • every other cell had an extra Y chromosome
  19. XY/ XYY
    • two cell lines
    • one was a normal male line and the other was trisomic
    • three copies of each chromosome in each trisomic cell
  20. XY/XXY/XXYY
    • three cell lines
    • one normal male line, one line where each cell has an extra X chromosome and one line where each cell has two extra chromosomes
  21. Abnormalities of sex differentiation
    • freemartin
    • mutation of the Tdy gene (or any others involved in sex differentiation)
    • mutation of an X-linked gene
    • abnormal number of chromosomes - excess of X chromosomes or too few
    • abnormal number of X chromosomes together with a Y chromosome (XXY)
    • true hemaphrodites
  22. Freemartin
    • sterile female
    • fusion of blood vessels in multiple conceptions
    • secretions from male embryo can affect the development of a female twin embryo
  23. Mutation of Tdy or othersex-differentiation gene
    animals develop as intersexes
  24. Mutation of an X-linked gene
    • target organs cannot respond to the secretion of testosterone
    • will see feminized males - not normal development of testes
    • mutated gene - testicular feminization gene (Tfm)
  25. Kleinfelter syndrome
    • XXY
    • affected individuals are:
    • - phenotypic males (Y chromosome)
    • - infertile (presence of 2 X chromosomes blocks spermatogenesis)
  26. True Hermaphrodites
    animal has both a complete ovary and a complete testis
  27. Intersexes
    pseudohermaphrodites
  28. Intersexuality
    animal has morphological aspects of both a male and a female
  29. Intersexuality in the dog and cat
    • more common in the dog than the cat
    • more common in pigs
    • dog presents as a female that does not come into season
    • 1. gonads do not develop properly and remain undifferentiated or are ovo-testes (properties of both)
    • - to determine this, send out for histopathology
    • 2. tubular genetalia do not develop normally (urinary problems)
    • - urine from bladder pools in a urogenital sinus instead of being expelled through a vagina and vestibule
    • - causes bacterial urine infection
    • 3. Urethra is narrower than normal
    • - bladder stones
    • - urethral blockage (urinary stasis)
    • 4. enlarged clitoris
    • - rubbing
    • - licking
    • -soreness
    • 5. genetic females (XX)
    • 6. genetic males (XY)
    • - female phenotype with some male characteristics
    • male tortis are not intersexes because they do not have any development of the female reproductive system

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