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First Aid STEP 1 - Biochemistry > Biochemistry - Genetics > Flashcards

Biochemistry - Genetics Flashcards

1
Q

Uniparental disomy

A

Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent

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2
Q

Hardy-Weinberg population genetics

A

If a population is in Hardy-Weinberg equilibrium and if p and q are the frequencies of separate alleles, then:

p-squared + 2pq + q-squared = 1 and p +q = 1

p-squared = frequency of homozygosity for allele p
q-squared = fréquence of homozygosity for allele q
2pq = frequency of heterozygosity
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3
Q

What are the Hardy-Weinberg law assumptions?

A
  1. No mutation occurring at the locus
  2. Natural selection is not occurring
  3. Completely random mating
  4. No net migration
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4
Q

Imprinting

A

Imprinting/Inactivation by methylation

only one allele active and the other is inactive

With one allele inactivated, deletion of the active allele –> disease

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5
Q

What is the pathogenesis of Prader-Willi Syndrome?

A

maternal imprinting

mutation on chromosome 15 of PATERNAL gene

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6
Q

What are symptoms of Prader-Willi Syndrome?

A 
hyperphagia
obesity
intellectual disability
hypogonadism
hypotonia
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7
Q

What is the pathogenesis of AngelMan Syndrome?

A

paternal imprinting

mutation on chromosome 15 of MATERNAL gene

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8
Q

What are symptoms of AngelMan Syndrome?

A

inappropriate laughter
seizures
ataxia
severe intellectual disability

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9
Q

What mode of inheritance affects both male and females in all generations?

What is the inheritance often due to?

A

autosomal dominant

due to structural genes

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10
Q

What mode of inheritance is usually only seen in 1 generation?

What is the inheritance often due to?

A

autosomal recessive

enzyme deficiencies

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11
Q

What mode of inheritance results in sons of heterozygous mothers having a 50% chance of being affected?

A

X-linked recessive

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12
Q

Can male-to-male transmission occur in X-linked recessive?

A

NO

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13
Q

Effects in a male from an X-linked recessive inheritance are more or less severe?

A

MORE

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14
Q

What is mitochondrial inheritance?

A

transmitted only through the mother

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15
Q

Who shows signs of disease in mitochondrial inheritance?

A

All offspring of affected females may show signs of disease

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16
Q

What diseases are associated with mitochondrial inheritance?

A

Mitochondrial myopathies (rare disorders)

often present with myopathy, lactic acidosis, and CNS

secondary to failure in oxidative phosphorylation

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17
Q

What can be seen on muscle biopsy of a mitochondrial myopathy?

A

“ragged red fibers”

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18
Q

What are autosomal dominant diseases (alphabetical order)?

A 
Autosomal Dominant Polycystic Kidney Disease (ADPKD)- chrom 16
Familial Adenomatous Polyposis - chrom 5
Familial Hypercholesteremia 
Hereditary spherocytosis
Huntington's Disease
Marfan Syndrome
Multiple Endocrine Neoplasias
Neurofibromatosis Type 1
Neurofibromatosis Type 2
Tuberous sclerosis
von Hippel-Lindau Disease
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19
Q

What are autosomal recessive diseases (alphabetical order)?

A 
albinism
ARPKD
CF
glycogen storage diseases
hemochromatosis
Kartagener Syndrome
mucopolysaccharidoses
PKU
sickle cell anemia
sphingolipidoses
thalassemias
Wilson Disease
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20
Q

What is the most common lethal genetic disease in Caucasian population?

A

Cystic fibrosis

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21
Q

What is the defect in CF?

A

defect in CFTR gene on chromosome 7

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22
Q

What are signs to diagnose CF?

A
  1. increased Cl- concentration in sweat = diagnostic!
  2. contraction alkalosis and hypokalemia (similar to a diuretic in that H2O/Na+ losses results in concomitant renal K+/H+ wasting)
23
Q

What are complications of CF?

A 
recurrent pulmonary infxns (e.g. Pseudomonas)
chronic bronchitis and bronchiectasis --> reticulonodular pattern on CXR
pancreatic insufficiency
malabsorption and steatorrhea
nasal polyps
meconium ileus in newborns
infertility in males
Fat soluble vit. deficiencies (ADEK)
24
Q

What is the treatment for CF?

A 
N-acetylcysteine - loosens mucus plugs
dornase alfa (DNAse) - clear leukocytic debris
25
Q

What are X-linked Recessive diseases?

A 
Bruton agammaglobulinemia
Wiskott-Aldrich Syndrome
Fabry Disease
G6PD Deficiency
Ocular albinism
Lesch-Nyhan Syndrome
Duchenne (and Becker) muscular dystrophy
Hunter
Syndrome
Hemophilia A and B
Ornithine transcarbamylase deficiency
26
Q

What is the pathogenesis of Duchenne Muscular Dystrophy?

A

X-linked frameshift mutation –> truncated dystrophin –> accelerated muscle breakdown

27
Q

What tests are needed to confirm Duchenne Muscular Dystrophy?

A

Western blot and muscle biopsy

28
Q

What lab findings will you see in Duchenne Muscular Dystrophy?

A

Increased CPK and aldolase

29
Q

When do DMD symptoms begin?

A

Before age 5

30
Q

What is the pathogenesis of Becker Disease?

A

X-linked POINT mutation –> defunct dystrophin protein –> less severe than Duchenne Muscular Dystrophy

31
Q

When do Becker Disease symptoms begin?

A

adolescence or early adulthood

32
Q

What is the pathogenesis of myotonic type 1 disease?

This is an example of muscular dystrophy.

A

CTG trinucleotide repeat expansion in the DMPK gene -> abnormal expression of myotonic protein kinase –> myotonia, muscle wasting, frontal balding, cataracts, testicular atrophy, and arrhythmia

33
Q

What is the pathogenesis of Fragile X Syndrome?

A

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

34
Q

What is a major finding of Fragile X Syndrome?

A

2nd most common cause of genetic intellectual disability (after Down syndrome)

35
Q

What are physician findings of Fragile X Syndrome?

A 
enlarged testes
long face with a large jaw
larged everted ears
autism
mitral valve prolapse
36
Q

What are diseases with trinucleotide repeat expansions?

A

Huntington disease
Myotonic dystrophy
Friedrich ataxia
fragile X syndrome

Try Hunting for my fried eggs.

37
Q

What is the MC cause of genetic intellectual disability?

A

Down Syndrome

38
Q

What trisomy is associated with Down Syndrome?

A

Trisomy 21

39
Q

What is the usual cause of Down Syndrome?

A

meiotic nondisjunction of homologous maternal age

40
Q

What are the lab findings during pregnancy with a diagnosis of Down Syndrome?

A

1st trimester - increased nuchal translucency and hypo plastic nasal bone, serum PAPP-A is decrease and free beta-hCG is increased

2nd trimester - increased beta-hCG and estriol and decreased inhibin A and alpha-fetoprotein

41
Q

What trisomy is associated with Edwards Syndrome?

A

Trisomy 18

42
Q

What are some signs of Edwards Syndrome?

A

low set ears
micrognathia
intellectual disability
rocker bottom feet

43
Q

What are the labs associated with Edwards Syndrome?

A

Decreased alpha-fetoprotein, estrial, beta-HCG, and inhibin-A

44
Q

What trisomy is associated with Patau Syndrome?

A

Trisomy 13

45
Q

What are some signs of Patau Syndrome?

A 
rocker bottom feet
polydactyly 
micropthalmia
cleft lip/palate
intellectual disability
46
Q

What is a Robertsonian Translocation?

What can it result in?

A

nonreciprocal chromosomal translocation where long arms of acrocentric chromosomes fuse at the centromere and the 2 short arms are lost

results in miscarriage, stillbirth, and chromosomal imbalance (e.g. Down Syndrome)

47
Q

What genetic abnormality is associated with Cri-du-chat Syndrome?

A

micro deletion of short arm of chromosome 5

48
Q

What are some findings of Cri-du-chat Syndrome?

A 
microcephay
mod-severe intellectual disability
high pitched crying/mewing* ("cry of the cat")
cardiac abnormalities (VSD)
epicanthal folds
49
Q

What genetic abnormality is associated with Williams Syndrome?

A

micro deletion long arm of chromosome 7

50
Q

What are some findings of Williams Syndrome?

A 
"elfin" facies
hypercalcemia
extreme friendliness w/ strangers
cardiac abnormalities
well-developed verbal skills
intellectual disablity
51
Q

What are the syndromes associated with deletions at 22q11?

A

DiGeorge Syndrome and Velocardiofacial Syndrome

52
Q

What is the pneumonic and findings associated with the 22q11 deletion diseases?

A

CATCH-22

Cleft palate
Abnormal facies
Thymic aplasia
Cardiac abnormalities
Hypocalcemia (d/t no parathyroids)
Deletion at chrom. 22
53
Q

What is the cause of DiGeorge Syndrome embryologically?

A

Failure of 3rd and 4th pharyngeal pouches to develop

First Aid STEP 1 - Biochemistry (8 decks)

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