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T&T General Genetics > TT General Genetics > Flashcards

TT General Genetics Flashcards

1
Q

What are the three alleles of the blood group locus?

A

A,B,O.

There is also the Rhesus antigen locus (Rh positive or Rh negative).

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2
Q

What is the inheritance pattern of the ABO blood group locus?

A

Codominance

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3
Q

Why is the O blood group clinically significant?

A

The O blood group allele results in the lack of expression of any of the A or B carbohydrate antigens. This means that the person with O,O will be A and B antibody positive.

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4
Q

Describe anti-blood group antibodies and their clinical significance.

A

People can be A, B or O blood groups. They are expressed co-dominantly, so an AB allele status individual expresses both blood groups.

-> A person who lacks a blood group will develop antibodies to it.  So:
OO -> Antibodies to A + B
AA -> Antibodies to B
AB -> No antibodies,
BB -> Antibodies to A.
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5
Q

How do the A and B blood groups differ?

A

The A and B blood groups encode for different carbohydrate surface antigens that are serologically different.

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6
Q

How many loss of function alleles are present in a normal persons genome?

A

Expect 50-200 LOF alleles in a person’s genome.

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7
Q

What is the risk of congenital anomalies in a 1st cousin marriage?

A

3-5%.

About twice the risk as normal.

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8
Q

What does fitness measure?

A

The percentage of people with a certain syndrome/genotype that successfully have kids.

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9
Q

What is confined placental mosaicism?

A

A variant that is found only in the extra embryonic tissue.

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10
Q

What is the frequency of Fragile X in live births?

A

1:4000

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11
Q

What is the penetrance of the Fragile X allele in women?

A

50-60%

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12
Q

What is the Fragile X premutation allele?

A

56-200 repeats

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13
Q

Where is the Fragile X repeat located?

A

5’ UTR, expansion results in methylation

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14
Q

In what sex does the Fragile X premutation allele expand?

A

In women

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15
Q

What is the mitochrondria genetic bottleneck?

A

Mom reduces the number of mitochondria allowed into an oocyte, then massively expands them. Results in a shift in allele frequency in the oocyte mitochondria.

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16
Q

What is allelic heterogeneity?

A

Different variants in one gene can cause the same phenotype

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17
Q

What is locus heterogeneity?

A

Different genes can cause the same phenotype

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18
Q

What is phenotypic heterogeneity?

A

Different variants in one gene can cause a different phenotype

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19
Q

What is the calculation for relative risk?

A

p(Disease in family of affected) / p(Disease in general population)

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20
Q

How do you measure twin heritability of a complex quantitative trait?

A

2 x (Measure correlation in monozygotic twins, subtract from correlation in dizygotic twins)

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21
Q

What is the heritability of schizophrenia?

A

60% heritability in monozygotic twins

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22
Q

If women are resistant to a complex disease, is the son of an affected mother more or less likely to get the disease?

A

Tests disease burden threshold model. Affected women must have a higher genetic burden, so a son of an affected women would inherit MORE burden and be more likely to have disease.

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23
Q

What are the two known CFTR modifiers?

A

MBL2 -> A mannose binding lectin that removes bacterial pathogens

TGFB1 -> TGFB1 variants promoter CFTR lung fibrosis and scarring

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24
Q

What genes show digenic inheritance?

A

Retinis Pigmentosa -> Peripherin + Rom1

Bardet Beidl -> Get disease is HOM at one site and het at another.

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25
Q

What are the genetic and environmental risk factors for thrombophilia?

A
  1. Factor V Leiden (Arg506Gln)
  2. Prothrombin (3’UTR c.20210G>A)
  3. Use of oral contraceptives
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26
Q

Your patient wants to go on birth control, what gene should be tested to evaluate for clotting risk?

A

Prothrombin 3’UTR variant c.20210G>A.

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27
Q

Your patient has Prothrombin 3’UTR variant c.20210G>A and is on oral contraceptives - what is the elevated risk of clotting?

A

30-150 fold higher risk.

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28
Q

Familial Hirschsprung disease is caused by what gene?

29
Q

What is the location and size of the MHC locus?

A

3MB on Chr 6.

30
Q

How many genes and alleles are in the MHC locus?

A

200 genes, over 2000 alleles

31
Q

What are the MHC I genes?

A

HLA-A, HLA-B, HLA-C

32
Q

What are the MHC II genes?

A

HLA-DR, HLA-DQ, HLA-DP

33
Q

What is the allele associated with late onset Alzheimer’s disease?

A

APOE-E4 is associated with late onset Alzheimer’s
-> Exhibits incomplete dominance

-> Mendelian Alzheimers is associated with PSEN1, PSEN2, BAPP

34
Q

Describe what an amyloid is

A

Amyloids are aggregates of proteins that result when proteins lose their normal 3’ structure and form clumps in the cell or extracellular space.

35
Q

What is the target allele and mechanism for Lumacaftor?

A

Corrects CFTR deltaF508 folding defect.

36
Q

What is the target allele and mechanism for Ivacaftor?

A

Molecular potentiator that improves the function of CFTR Gly551Asp. Only approved for 9 CFTR alleles in total.

37
Q

What are pros/cons of retroviruses for gene therapy?

A

8kb loading, does not integrate into non-dividing cells, exhibits integration bias.

38
Q

What are pros/cons of lentiviruses for gene therapy?

A

HIV derived. Integrates into non-dividing cells, no integration site bias.

39
Q

What are pros/cons of AAV for gene therapy?

A

5kb loading, transduces non-dividing cells. Low immunogenicity. Episomal payload expression (low integration rate).

40
Q

What are pros/cons of Adenoviruses for gene therapy?

A

30kb loading. High immunogenicity (one death is associated with Adenovirus treatment immune response).

41
Q

Define malformation

A

A birth defect that results from intrinsic defects in the genetic program (IE SLOS)

42
Q

Define deformation:

A

A birth defect caused by extrinsic factors causing physical changes (IE congenital arthrogryposis)

43
Q

Define disruption

A

A birth defect that results from the destruction of irreplaceable tissue.

44
Q

Describe Pierre-Robin sequence:

A
  1. Small jaw results in posterior placement of tongue.
  2. Posterior tongue results in palatal fusion failure.
  3. Results in U-shaped clefting + microretrognathia.
45
Q

What syndromes can cause Pierre-Robin sequence?

A

Stickler syndrome

46
Q

How can you differentiate between multi-factorial clefting and Pierre-Robin clefts?

A

Pierre-Robin clefts are U-shaped.

Classic clefts are V-shaped.

47
Q

When does gastrulation occur in human embryos?

A

After implantation, around day 12.

48
Q

What are the three embryonic germ layers?

A

Endoderm
Mesoderm
Ectoderm

49
Q

What tissues does the endoderm generate?

A

Central core of organism:

  • Gut cavity cells
  • Airways
50
Q

What tissues does the mesoderm generate?

A

Organs + structure

  • Kidney
  • Heart
  • Bone
  • Muscle
51
Q

What tissues does the ectoderm generate?

A

CNS
Peripheral Nervous System
Skin

52
Q

What is a zygote?

A

A fertilized egg

53
Q

What is an embryo?

A

Human @ fertilization till 9 weeks development.

54
Q

What is a fetus?

A

Human @9 week - birth

55
Q

When in development do neural tube defects occur?

A

IN THE 1st 4 weeks of pregnancy.

56
Q

What are the risk factors for neural tube defects.

A

LOW FOLATE (Vitamin B9) (Less < 200 ug/L)

  • > MTHFR polymorphism linked to NTD with low folate levels.
  • > Low Vitamin B12 might also play a role.
57
Q

What is the screening method for Neural tube defects?

A

High alpha-fetoprotein on maternal serum screening

58
Q

What are the two types of Neural tube defects?

A

Anencephaly

Spina bifida.

59
Q

What is the recommended folate dosage and supplementation time for women considering pregnancy?

A

400-800 ug/day Folate starting one month prior to pregnancy, continuing for 2 months into the pregnancy.

60
Q

What are ACOG recommendations for invasive prenatal testing availability?

A

Provide invasive prenatal testing to all interested women/couples.

61
Q

What are ACOG recommendations for 1st line testing?

A

ACOG recommends use of CMA over karyotyping for first line testing.

62
Q

What are typical indications for invasive prenatal testing?

A
  1. Previous child with chromosomal defects (de novo or inherited)
  2. Presence of genomic abnormality in parents.
  3. Family history of genetic disease.
  4. Risk for NTD.
  5. Abnormal serum screen/NIPS results.
  6. Mom wants invasive testing.
63
Q

What are the analytes in the 1st trimester screen?

A

PAPP-A (Pregnancy associated plasma protein A)
hCG (human chioronic gonadotrophin)
Nuchal translucency

64
Q

Describe the possible results/interpretation of a 1st trimester serum screen for PAPP-A:

A

LOW PAPP-A in all trisomies.

Normal otherwise.

65
Q

Describe the possible results/interpretation of a 1st trimester serum screen for hCG:

A
  • Elevated hCG in trisomy 21.

- LOW hCG in all other trisomies.

66
Q

Describe the possible results/interpretation of a 1st trimester serum screen for nuchal translucency

A

HIGH NT in trisomy 13, 18, 21 and 45,X.

67
Q

What are the analytes in a 2nd trimester serum screen?

A

uE3 -Unconjugated estriol
AFP - Alpha fetoprotein
hCG - human chioronic gonadotrophin
Inhibin A

68
Q

Describe the possible results of a 2nd trimester serum screen by analyte

A

uE3: Down in any trisomy
AFP: - Elevated in NTD, down in trisomy
hCG: - HIGH in trisomy 21, low in all other trisomies
Inhibin A: LOW in trisomy 21, normal in all other trisomies.

69
Q

What are the common causes of elevated AFP?

A
  • Neural tube defects
  • Omphalocoele
  • Fetal demise
  • Twin pregnancy
  • False positive due to over-estimation of fetal age.

T&T General Genetics (1 decks)

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