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T&T General Genetics > TT General Genetics > Flashcards

TT General Genetics Flashcards

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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
What are the genetic and environmental risk factors for thrombophilia?
1. Factor V Leiden (Arg506Gln) 2. Prothrombin (3'UTR c.20210G>A) 3. Use of oral contraceptives
26
Your patient wants to go on birth control, what gene should be tested to evaluate for clotting risk?
Prothrombin 3'UTR variant c.20210G>A.
27
Your patient has Prothrombin 3'UTR variant c.20210G>A and is on oral contraceptives - what is the elevated risk of clotting?
30-150 fold higher risk.
28
Familial Hirschsprung disease is caused by what gene?
RET
29
What is the location and size of the MHC locus?
3MB on Chr 6.
30
How many genes and alleles are in the MHC locus?
200 genes, over 2000 alleles
31
What are the MHC I genes?
HLA-A, HLA-B, HLA-C
32
What are the MHC II genes?
HLA-DR, HLA-DQ, HLA-DP
33
What is the allele associated with late onset Alzheimer's disease?
APOE-E4 is associated with late onset Alzheimer's -> Exhibits incomplete dominance -> Mendelian Alzheimers is associated with PSEN1, PSEN2, BAPP
34
Describe what an amyloid is
Amyloids are aggregates of proteins that result when proteins lose their normal 3' structure and form clumps in the cell or extracellular space.
35
What is the target allele and mechanism for Lumacaftor?
Corrects CFTR deltaF508 folding defect.
36
What is the target allele and mechanism for Ivacaftor?
Molecular potentiator that improves the function of CFTR Gly551Asp. Only approved for 9 CFTR alleles in total.
37
What are pros/cons of retroviruses for gene therapy?
8kb loading, does not integrate into non-dividing cells, exhibits integration bias.
38
What are pros/cons of lentiviruses for gene therapy?
HIV derived. Integrates into non-dividing cells, no integration site bias.
39
What are pros/cons of AAV for gene therapy?
5kb loading, transduces non-dividing cells. Low immunogenicity. Episomal payload expression (low integration rate).
40
What are pros/cons of Adenoviruses for gene therapy?
30kb loading. High immunogenicity (one death is associated with Adenovirus treatment immune response).
41
Define malformation
A birth defect that results from intrinsic defects in the genetic program (IE SLOS)
42
Define deformation:
A birth defect caused by extrinsic factors causing physical changes (IE congenital arthrogryposis)
43
Define disruption
A birth defect that results from the destruction of irreplaceable tissue.
44
Describe Pierre-Robin sequence:
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
What syndromes can cause Pierre-Robin sequence?
Stickler syndrome
46
How can you differentiate between multi-factorial clefting and Pierre-Robin clefts?
Pierre-Robin clefts are U-shaped. | Classic clefts are V-shaped.
47
When does gastrulation occur in human embryos?
After implantation, around day 12.
48
What are the three embryonic germ layers?
Endoderm Mesoderm Ectoderm
49
What tissues does the endoderm generate?
Central core of organism: - Gut cavity cells - Airways
50
What tissues does the mesoderm generate?
Organs + structure - Kidney - Heart - Bone - Muscle
51
What tissues does the ectoderm generate?
CNS Peripheral Nervous System Skin
52
What is a zygote?
A fertilized egg
53
What is an embryo?
Human @ fertilization till 9 weeks development.
54
What is a fetus?
Human @9 week - birth
55
When in development do neural tube defects occur?
IN THE 1st 4 weeks of pregnancy.
56
What are the risk factors for neural tube defects.
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
What is the screening method for Neural tube defects?
High alpha-fetoprotein on maternal serum screening
58
What are the two types of Neural tube defects?
Anencephaly | Spina bifida.
59
What is the recommended folate dosage and supplementation time for women considering pregnancy?
400-800 ug/day Folate starting one month prior to pregnancy, continuing for 2 months into the pregnancy.
60
What are ACOG recommendations for invasive prenatal testing availability?
Provide invasive prenatal testing to all interested women/couples.
61
What are ACOG recommendations for 1st line testing?
ACOG recommends use of CMA over karyotyping for first line testing.
62
What are typical indications for invasive prenatal testing?
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
What are the analytes in the 1st trimester screen?
PAPP-A (Pregnancy associated plasma protein A) hCG (human chioronic gonadotrophin) Nuchal translucency
64
Describe the possible results/interpretation of a 1st trimester serum screen for PAPP-A:
LOW PAPP-A in all trisomies. | Normal otherwise.
65
Describe the possible results/interpretation of a 1st trimester serum screen for hCG:
- Elevated hCG in trisomy 21. | - LOW hCG in all other trisomies.
66
Describe the possible results/interpretation of a 1st trimester serum screen for nuchal translucency
HIGH NT in trisomy 13, 18, 21 and 45,X.
67
What are the analytes in a 2nd trimester serum screen?
uE3 -Unconjugated estriol AFP - Alpha fetoprotein hCG - human chioronic gonadotrophin Inhibin A
68
Describe the possible results of a 2nd trimester serum screen by analyte
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
What are the common causes of elevated AFP?
- 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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