Genetics Questions

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Genetics Questions
2010-12-18 20:01:40
Genetics prenatal screening

Prenatal screening, genetics
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  1. How many DNA bases are packed around a histone?
    140-150 DNA bases
  2. In which direction does DNA replication and RNA synthesis proceed?
    From the 5' end to the 3' end
  3. DNA polymerase adds free nucleotides to which end of the new DNA strand?
    the 3' end
  4. What is the funtion of replication bubbles?
    To allow DNA replication to happen faster
  5. Where does RNA polymerase bind to begin mRNA synthesis?
    Promoter site on the DNA
  6. The template strand is also referred to as...
    the antisense strand
  7. What is the 5' cap?
    Chemically modified guanine nucleootides added to the 5' end of new RNA molecule

    Keeps mRNA from being degraded during synthesis
  8. What is the Poly-A tail?
    • 100-200 adenine bases added to the 3' end of mRNA
    • Stabilizes mRNA
  9. What are housekeeping genes?
    Genes transcribed in all cells of the body that encode products that are required for a cell's maintenance and metabolism
  10. Name three important transcription factors
    • Homeobox-containing genes (HOX, PAX)
    • SOX genes (SRY)
    • GLI (involved in hedgehog signalling pathways)
  11. What are HOX genes?
    • Highly conserved developmental genes
    • 3' genes expressed anteriorly and earlier than 5' genes
    • Forms a posterior/anterior axis
  12. Effects of HOX genes in development
    • HOX gene products are molecular switches (transcription factors)
    • Promotes cell division, adhesion, apoptosis and cell migration
  13. Where will descendents of SHH show up?
  14. Diagnostic sensitivity compares
    the true positives and false negatives in a clinical test
  15. What are characteristics of a highly sensitive test?
    • The number of false negatives is very low
    • A negative result is a reliable way to rule OUT a disease
    • "SNOUT"
  16. Diagnostic specificity compares...
    True negatives to falso positives in a clinical test
  17. Characteristics of a highly specific test
    • The number of false positives is very low
    • A positive result is a reliable way to rule IN a disease
    • "SPIN"
  18. What prenatal tests can be done during the 1st trimester?
    • 1. Chorionic Villus Sampling (CVS)
    • 2. First trimester screen (ultrasound, PAPP-A and BhCG)
  19. When does BhCG first appear in serum?
    At 2 weeks
  20. What does a first trimester screen consist of?
    • 1. Ultrasound
    • 2. PAPP-A
    • 3. BhCG
  21. What prenatal tests can be done in the second trimester?
    • 1. Triple screen
    • 2. Quad screen
    • 3. Penta screen
    • 4. Amniocentesis
    • 5. Cordocentesis
  22. What does MSAFP stand for?
    Maternal serum alpha fetal protein
  23. Which of the second trimester tests are NOT invasive?
    • Triple screen
    • Quad screen
    • Penta screens
    • (these are maternal blood tests)
  24. Which tests can be done in the third trimester?
    • 1. Biophysical profile
    • 2. Fetal movement monitoring
    • 3. Contraction stress test
    • 4. Glucose challenge screening and glucose tolerance test
    • 5. Group B strep test
  25. What is the most common risk threshold?
  26. What are the current ACOG guidelines for prenatal testing?
    • 1. All pregnant women should be offered screening of down syndrome, regardless of maternal age
    • 2. Ideally should be done BEFORE week 20
    • 3. Non-invasive screening tests are much more reliable than they once were
  27. When are non-invasive screening tests the most reliable?
    Before week 20
  28. What information can you obtain from an ultrasound?
    • 1. Placental and fetal size
    • 2. Multiple fetuses
    • 3. Placental abnormalities
    • 4. Abnormal presentations of the fetus
    • 5. Estimation of fetal age
  29. Screening for what is useful to detect Down Syndrome in the late first trimester?
    nuchal translucency
  30. When/ How is PAPP-A measured?
    From the maternal serum in the 1st trimester
  31. What are low levels of PAPP-A associated with?
    • 1. Trisomy 13, 18 and 21
    • 2. Small for gestational age
    • 3. Stillbirth
  32. What are high levels of PAPP-A associated with?
    Large for gestational age
  33. Where is B-hCG produced and where is it found?
    In the syncytiotrophoblast and enters the maternal bloodstream
  34. What does B-hCG do?
    It maintains the hormonal activity of the corpus luteum during pregnancy
  35. When does B-hCG show up in urine?
    3 weeks
  36. In which trimesters can B-hCG be used for screening?
    1st and 2nd trimesters
  37. When can fetal cells be detected in the maternal blood stream?
    As early as 8 weeks
  38. What types of fetal cells can be found in the maternal blood stream?
    • 1. Trophoblasts
    • 2. Lymphocytes
    • 3. Granulocytes
    • 4. Stem cells
    • 5. Nucleated erythrocytes
  39. Which fetal cell that is found in maternal blood is preferred for testing purposes?
    nucleated erythrocytes
  40. Why are nucleated erythrocytes perferred for prenatal screening?
    • Because they are short-lived in the blood stream
    • (You know you're not collecting a sample from a pervious pregnancy)
  41. What does a KB test detect?
    • Kleihaur-Betke test
    • Detects maternal hemmorage and helps determine amount of Rhogam to use in erythroblastosis fetalis
  42. What is Chorionic Villus Samping used for?
    To obtain a karyotype
  43. When is CVS performed?
    between the 10th and 12th weeks
  44. What is the risk of miscarriage for CVS?
  45. What molecules does a triple screen test?
    • MSAFP
    • UE3
    • B-hCG
  46. When is a triple screen performed?
    In the second trimester around the 16th week
  47. What does interpretation of the triple screen rely heavily upon?
    gestational age
  48. What is MSAFP?
    • Maternal Serum Alpha Fetal Protein
    • A large serum glycoprotein
  49. Where is MSAFP synthesized?
    In the fetal liver, umbilical vesicle and gut
  50. What is the normal level of MSAFP in a non-pregnant woman or man?
    0-40 mcg/L
  51. What is the normal level of MSAFP in a woman that is 10-15 weeks pregnant?
    10-150 mcg/L
  52. When do AFP levels in fetal serum peak?
    around week 14
  53. AFP in the amniotic fluid is normally found in (high or low) concentrations
  54. High levels of AFP in the amniotic fluid can indicate...
    Neural tube defects or abdominal wall defects
  55. Higher levels of AFP are seen in these women, regardless of fetus
    • African american women
    • Diabetic women
    • Obeses women
  56. Lowest levels of AFP are seen in this ethnicity
    Asian women
  57. AFP is checked by which test?
  58. High levels of AFP in non-pregnant adults are associated with...
    • 1. Testicular or Ovarian cancer
    • 2. Liver disease
    • 3. Alcohol abuse
  59. AChE should never be found in...
    amniotic fluid
  60. Which gene is important in supressing cancer cells?
  61. Where can UE3 be detected?
    In mother's blood and urine
  62. How do the levels of UE3 change in the third trimester?
    • They normally increase throughout the third trimester
    • A sudden drop indicates a threatened fetus
  63. Low levels of UE3 are associtated with
    Trisomy 18 and 21
  64. In a triple screen a neural tube defect would show...
    • High MSAFP
    • Normal UE3
    • Normal B-hCG
  65. In a triple screen trisomy 21 would show...
    • Low MSAFP
    • Low UE3
    • High B-hCG
  66. In a triple screen trisomy 18 would show...
    • Low MSAFP
    • Low UE3
    • Low B-hCG
  67. In a triple screen molar pregnancy would show...
    • Low MSAFP
    • Low UE3
    • Very high B-hCG
  68. In a triple screen multiple fetuses would show...
    • High MSAFP
    • Normal UE3
    • High B-hCG
  69. In a triple screen fetal death would show...
    • High MSAFP
    • Low UE3
    • Low B-hCG
  70. What molecules does a quad screen test for?
    • MSAFP
    • UE3
    • B-hCG
    • Inhibin A
  71. Where is inhibin A secreted?
    by placenta and corpus luteum
  72. What are high levels of inhibin A associated with?
    Increased risk for trisomy 21 and preterm delivery
  73. What does inhibin A do?
    Down regulates FSH synthesis and inhibits its secretion by the anterior pituitary gland
  74. Which precentage of pregnancies with chromosomal abnormalities can be detected with a quad screen?
  75. What molecules does a penta screen test?
    • 1. MSAFP
    • 2. UE3
    • 3. B-hCG
    • 4. Inhibin A
    • 5. hyperglycosylated hCG (h-hCG)
  76. Elevated levels of h-hCG/ invasive trophonlast antigen are associated with..
    Trisomy 21
  77. What are the risks of amniocentesis?
    • miscarriage 1/200
    • maternal Rh sensitization
  78. When can amniocenteis be performed?
    In the second trimester between weeks 16 and 20
  79. When is the earliest amniocentesis can be performed and why is this not advised?
    • 11 weeks
    • associated with respiratory effects
  80. How much amniotic fluid is taken out during an amniocenteis?
  81. How long are amniocytes typically cultured?
    7 days
  82. What information can be derived from an amniocentesis?
    • Biochemical assays
    • DNA-based diagnosis (PCRs)
    • Chromosome analysis (karyotype (slow), FISH (fast))
  83. Cordocentesis is also referred to as
    Percutaneous umbilical blood sampling (PUBS)
  84. When is the earliest PUBS can be performed?
    12 weeks
  85. From where is the fetal blood obtained?
    Umbilical vein, near the placenta
  86. What is Cordocentesis used for?
    • For rapid diagnosis of blood diseases
    • and to distinguish between true and falso fetal mosaism
  87. When is the earliest fetal transfusion can be performed?
    around 20- 22 weeks
  88. Which procedure can be performed on ANY fetal cell?
  89. What are advantages of FISH?
    • Can be used on interphase (you don't have to wait as long)
    • Able to detect small deletions, insertions and chromosomal rearrangements
  90. What is the resolution of FISH?
    1Mb (this is generally not possible in karyotyping)
  91. How long must cells be cultured in a karyotype?
    48-72 hours
  92. Which phase of mitosis do the fetal cells need to be arrested in for karyotypes?
  93. How long do FISH techniques take?
    2 days
  94. In how many chromosomal pairs does FISH detect problems?
    In 9 of the 23 chromosomal pairs
  95. When is Biophysical Profiling performed?
    In the third trimester, after 24-26 weeks
  96. What are the 5 attributes of biophysical profiling?
    • 1. Breathing
    • 2. Movement
    • 3. Muscle tone
    • 4. Heart rate
    • 5. Amniotic fluid
  97. Biophysical profile: Normal breathing
    1 breathing episode in 30 minutes
  98. Biophysical profiling: movement
    2 or more moving episodes in 30 minutes
  99. Biophysical profiling: Muscle tone
    1 or more episodes of flexion or extension of limbs
  100. Biophysical profiling: heart rate
    2 or more episodes of reactive heart accelerations in 20 minutes
  101. Biophysical profiling: Amniotic fluid
    1 or more adequate pockets of amniotic fluid