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Biochem > genetics > Flashcards

genetics Flashcards

1
Q

variable expression

A

nature and severity of phenotype vary from one person to another

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2
Q

incomplete penetrance

A

not all individuals with a mutant genotype show the mutant phenotype

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3
Q

pleiotropy

A

one gene has more than one effect on phenotype (i.e. MULTIPLE phenotypes, seemingly unrelated)

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4
Q

imprinting

A

differences in phenotype depend on whether mutation is of maternal or paternal origin

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5
Q

anticipation

A

severity of disease worsens OR
age of onset of disease is early
in succeeding generations

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6
Q

loss of heterozygosity

A

if a pt inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted or mutated before cancer develops (TWO-HIT HYPOTHESIS).

*not true of oncogenes

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7
Q

dominant negative mutation

A

exerts dominant effect.

heterozygote produces nonfunctional altered protein that also prevents normal gene product from functioning.

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8
Q

linkage disequilibrium

A

tendency for certain alleles at 2 linked loci to occur together more often than expected by chance.

measure in POPULATION, not family.
often varies in diff pops.

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9
Q

mosaicism

A

occurs when cells in body differ in genetic makeup due to postfertilization loss of genetic info during mitosis

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10
Q

germline (gonadal) mosaicism

A

produce disease that is not carried by parents’ somatic cells

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11
Q

locus heterogeneity

A

mutations at diff loci can produce same phenotype

ex: Marfan, MEN 2B, and homocystinuria (all produce marfanoid habitus)

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12
Q

heteroplasmy

A

presence of both normal and mutated mtDNA, resulting in variable expression of mitochondrial inherited dz

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13
Q

uniparental disomy

A

offspring receives 2 copies of chromosomes from 1 parent and no copies from other parent

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14
Q

Hardy-Weinberg law assumes…

A
  1. no mutation occurring at locus.
  2. no selection for any of the genotypes at the locus.
  3. completely random mating.
  4. no migration.
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15
Q

cause of imprinting

A

at some loci, only ONE allele is active - the other is inactive (imprinted/inactivated by methylation).

with one allele inactivated, deletion of the ACTIVE ALLELE = disease.

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16
Q

Prader-Willi syndrome

A

imprinting.
chromo 15.

maternal allele inactivated.
Paternal allele should be active but is not expressed.

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17
Q

features of Prader-Willi

A 
mental retardation.
hyperphagia.
obesity.
hypogonadism.
hypotonia.
short stature.
thirst.
emotional lability.
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18
Q

AngelMan’s syndrome

A

imprinting.
chromo 15.

paternal allele inactivated.
Maternal allele should be active but is not expressed.

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19
Q

features of Angelman’s syndrome

A 
mental retardation.
seizures.
ataxia.
inappropriate laughter.
HAPPY PUPPET.
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20
Q

which mode of inheritance is often due to defects in structural genes?

A

AD

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21
Q

which mode of inheritance is often pleiotropic?

A

AD

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22
Q

which mode of inheritance often presents clinically after puberty?

A

AD

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23
Q

for which mode of inheritance is fam hx crucial for dx?

A

AD

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24
Q

which mode of inheritance is often due to enzyme deficiencies?

A

AR

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25
Q

how does AR compare to AD clinically?

A

AR more severe,

present in childhood.

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26
Q

which mode of inheritance is usually seen in only one generation?

A

AR

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27
Q

which mode of inheritance has NO MALE-to-MALE transmission?

A

X-linked R

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28
Q

which mode of inheritance guarantees disease in female offspring of affected father?

A

X-linked D

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29
Q

hypophosphatemic rickets

A

X-linked D disorder with increased phosphate wasting at prox tubule. presents like rickets.

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30
Q

which mode of inheritance is ONLY transmitted through MOTHER?

A

mitochondrial

all offspring may show signs of disease

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31
Q

which mode of inheritance is often due to failures in oxidative phosphorylation?

A

mitochondrial

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32
Q

why do mitochondrial disease have variable expression?

A

heteroplasmy

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33
Q

mitochondrial myopathies

A

ragged red fibers on microscopy due to abn mito accumulation under sarcolemma.

  1. Leber’s hereditary optic neuropathy.
  2. myoclonic epilepsy.
  3. mitochondrial encephalopathy.
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34
Q

mitochondrial myopathy: Leber’s hereditary optic neuropathy

A

acute loss of central vision

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35
Q

mitochondrial myopathy: mitochondrial encephalopathy

A

stroke-like episodes.

lactic acidosis.

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36
Q

AR disorders

A 
albinism.
ARPKD.
CF.
glycogen storage.
hemochromatosis.
mucopolysaccharidoses (except Hunter's).
PKU.
sickle cell.
sphingolipidoses (except Fabry's). 
thalassemias.
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37
Q

cystic fibrosis

A

AR defect in CFTR gene.
chromo 7.
deletion of Phe508.

38
Q

CFTR channel

A

actively secretes Cl in lungs and GI tract.
actively reabsorbes Cl from sweat.

activated by cAMP-mediated phosphorylation.

gated by ATP.

39
Q

what does the CFTR mutation do?

A

cause abnormal protein folding (defective glycosylation), resulting in DEGRADATION of channel before it reaches cell surf.

40
Q

clinical features of CF

A

defective Cl channel = secretion of abnormally thick mucus that plugs lungs, pancreas, liver.

recurrent pulmo infx.
chronic bronchitis.
bronchiectasis.
pancreatic insuff.
nasal polyps.
meconium ileus in newborn.
41
Q

what microorganisms tend to cause pulmo infx in CF?

A

Pseudomonas.

S.aureus.

42
Q

what is the result of pancreatic insuff in CF?

A

malabsorption.
fat-soluble vit deficiency.
steatorrhea.

failure to thrive in infancy.

43
Q

how does CF cause infertility in males?

A

BILATERAL absence of vas deferens

44
Q

DX of CF

A

increased Cl ions in sweat test

45
Q

TX of CF

A

N-acetylcysteine:

loosens mucous plugs by cleaving disulfide bonds w/in mucous glycoproteins.

46
Q

X-linked recessive disorders

A

“Be Wise, Fool’s GOLD Heeds Silly Hope”

Bruton's agammaglobulinemia.
Wiskott-aldrich.
Fabry's dz.
G6PD def.
Ocular albinism/OTC def.
Lesch-nyhan.
Duchenne/becker MD.
Hunter's Syndrome.
Hemophilia a and b.
47
Q

why are female carriers rarely affected by X-linked recessive disorder?

A

random inactivation of X chromo in each cell

48
Q

Duchenne muscular dystrophy (DMD)

A

X-linked FRAME SHIFT mutation leading to DELETION of DYSTROPHIN GENE.

accelerated muscle breakdown.

49
Q

where does muscle weakness begin in DMD?

A

pelvic girdle mm.

progress superiorly.

50
Q

features of DMD

A 
muscle weakness.
walking difficulties (waddle).
calf PSEUDOHYPERTROPHY.
cardiac myopathy.
kyphoscoliosis.

onset before age 5.

51
Q

calf pseudohypertrophy in DMD

A

fibrofatty replacement of muscle

52
Q

what is the consequence of DMD gene being the longest known human gene?

A

increased rate of spontaneous mutation

53
Q

normal function of dystrophin

A

help anchor muscle fibers, primarily in skeletal and cardiac muscle

54
Q

Gower’s maneuver in DMD

A

child uses upper extremities to help in standing up from the ground

55
Q

DX of DMD

A

increase CPK (creatine phosphokinase).

muscle biopsy: varied fiber size and shape. increased conn tissue.

56
Q

Becker’s muscular dystrophy

A

X-linked mutated dystrophin gene.
less severe than DMD.
onset in adolescence or early adulthood.

57
Q

fragile X syndrome

A

X-linked defect affecting methylation and expression of FMR1 gene.

TRINUCLEOTIDE REPEAT disorder (CGG).

58
Q

findings in fragile X syndrome

A 
macro-orchidism.
long face, large jaw.
large everted ears.
autism.
mitral valve prolapse.

X-tra large testes, jaw, ears

59
Q

what is the 2nd most common cause of genetic MR?

A 
fragile X.
#1 is Down.
60
Q

trinucleotide repeat expansion disorders

A

Huntington’s.
Myotonic dystrophy.
Friedrich’s ataxia.
Fragile X syndrome.

61
Q

trinucleotide repeat in Huntington’s

A

CAG

62
Q

trinucleotide repeat in Myotonic dystrophy

A

CTG

63
Q

trinucleotide repeat in Friedrich’s ataxia

A

GAA

64
Q

trinucleotide repeat in Fragile X

A

CGG

65
Q

increased #trinucleotide repeats means…?

A

earlier onset of disease, increased severity (GENETIC ANTICIPATION)

66
Q

when does EXPANSION of trinucleotide repeats occur?

A

during parental transmission

67
Q

Down syndrome

A

trisomy 21.
most common chromo d/o.
most common cause of genetic MR.

68
Q

95% Down syndrome cases due to?

A

meiotic nondisjunction of homologous chromosomes- assoc with advanced maternal age

69
Q

4% Down syndrome cases due to ?

A

robertsonian translocation: break near centromeres, transfer of genetic material between chromos.

t(14;21) or t(21;22)

70
Q

1% Down syndrome cases due to?

A

Down mosaicism (no maternal assoc)

71
Q

findings in Down syndrome

A 
MR.
flat facies.
prominent epicanthal folds.
simian crease.
gap between 1st 2 toes.
cleft palate.
hypotonia.
*organ involvement*
72
Q

congenital heart defects in Down syndrome

A

most common: osmium primum-type ASD.

endocardial cushion defects.

73
Q

hematologic malignancy in Down syndrome

A 
increased risk of ALL.
also AML (M7).
74
Q

GI defect in Down syndrome

A

duodenal atresia

75
Q

neuro defect in Down syndrome

A

early-onset Alzheimer disease after age 35

76
Q

preg quad screen in Down syndrome

A

decrease AFP.
increase b-HCG.
decrease estriol.
increase inhibin A.

77
Q

ultrasound in Down syndrome

A

increase nuchal translucency

78
Q

Edwards syndrome

A

trisomy 18.

most common trisomy resulting in LIVE birth, following Down.

79
Q

findings in Edwards syndrome

A 
severe MR.
rocker bottom feet.
micrognathia (jaw).
low-set ears.
clenched hands**
prominent occiput.
cong heart dz.

death usually w/in 1 year.

80
Q

preg quad screen in Edwards syndrome

A

decrease AFP.
decrease b-HCG.
decrease estriol.
normal inhibin A.

81
Q

Patau syndrome

A 
trisomy 13. 
severe MR.
rocker bottom feet. 
microphthalmia.
microcephaly.
HOLOPROSENCEPHALY.
cleft lip/palate.
polydactyly.
cong heart dz.

death usually w/in 1 year.

82
Q

preg quad screen in Patau syndrome

A

normal AFP.
normal b-HCG.
normal estriol.
normal inhibin A.

83
Q

robertsonian translocation

A

nonreciprocal translocation when long arms of 2 acrocentric (centromeres near end) chromos fuse at the centromere and the short arms are lost

84
Q

chromos usually involved in robertsonian translocation are…?

A

pairs 13, 14, 15, 21, 22

85
Q

balanced robertsonian translocation

A

normally do not cause any abn phenotype

86
Q

unbalanced robertsonian translocation

A

miscarriage.
still birth.
chromo imbalance (trisomies).

87
Q

Cri-du-chat syndrome

A

congenital microdeletion of short arm of chromo 5 (5p-).

microcephaly.
moderate to severe MR.
HIGH-PITCHED crying/mewing.
epicanthal folds.
cardiac abn (VSD).
88
Q

Williams syndrome

A

congenital microdeletion of long arm chromo 7 (includes ELASTIN gene).

distinct "elfin" facies.
MR.
hypercalcemia (sensitive to vit D).
well-developed verbal skills.
extreme FRIENDLINESS with strangers.
cardio problems.
89
Q

22q11 deletion syndromes

A 
variable presentation: CATCH-22.
Cleft palate.
Abn facies.
Thymic aplasia (T cell def).
Cardiac defects.
Hypocalcemia second to parathyroid aplasia.
  • due to aberrant development of 3rd and 4th branchial/pharyngeal POUCHES.
  • includes DiGeorge and velocardiofacial syndromes
90
Q

DiGeorge syndrome

A

CATCH-22 with

thymic, parathyroid, cardiac defects

91
Q

velocardiofacial syndrome

A

CATCH-22 with

palate, facial, cardiac defects

Biochem (7 decks)

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