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Board Review > BIOCHEM--Genetics > Flashcards

BIOCHEM--Genetics Flashcards

1
Q

Genetic terms: codominance

A

both alleles contribute to the phenotype of a heterozygote

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2
Q

examples of codominance

A

blood groups A, B, AB;
alpha 1 antitrypsin deficiency;
HLA groups

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3
Q

Genetic terms: Variable expressivity

A

patients with the same genotype have varying phenotypes

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4
Q

Genetic terms: Incomplete penetrance

A

not all individuals with a mutant genotype show the mutant phenotype

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5
Q

Incomplete Penetrance:

risk of expressing phenotype=

A

% penetrance x probability of inheriting genotype

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6
Q

Example of variable expressivity

A

2 pt with NF 1 may have varying severity of disease

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7
Q

example of incomplete penetrance

A

BRCA1 mutations do not always result in breast or ovarian cancer

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8
Q

Genetic terms: Pleiotropy

A

one gene contributes to multiple phenotypic effects

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9
Q

Genetic terms: anticipation

A

increased severity or earlier onset of disease in each succeeding generation

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10
Q

Genetic terms: loss of heterozygosity

A

if a pt inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops. NOT TRUE OF ONCOGENES

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11
Q

Genetic terms: Dominant negative mutation

A

exerts a dominant effect. a heterozygote produces a non functional altered protein that also prevents the normal gene product from functioning.

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12
Q

Genetic terms: Linkage disequilibrium

A

tendency for certain alleles at 2 linked loci to occur together more or less often than expected by chance. Measured in population, not in family.
often varies in different populations

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13
Q

Genetic terms: mosaicism

A

presence of genetically distinct cell lines in the same individual

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14
Q

Genetic terms: somatic mosaicism

A

mutation arise from mitotic errors after fertilization and propagates throughout multiple tissues or organs

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15
Q

Genetic terms: gonadal mosaicism

A

mutation only in egg or sperm cells. if parents and relatives do not have the disease, suspect gonadal (or germline) mosaicism

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16
Q

Mosaicism example

A

McCune Albright Syndrome

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17
Q

McCune Albright Sundrome:

  1. mutation
  2. presentation
  3. prognosis
A
  1. muts affecting G-protein signaling
  2. unilateral cafe au lait spots w/ ragged edges, polyostotic fibrous dysplasia, and atleast one edocrinopathy
  3. lethal if mutation occurs before fertilization (affecting all cells), but survivable in pt with mosaicism
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18
Q

Genetic terms: locus heterogeneity

A

mutations at different loci can produce a similar phenotype

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19
Q

example of locus heterogeneity

A

albinism

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20
Q

Genetic terms: Allelic heterogeneity

A

different mutations in the same locus produce the same phenotype

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21
Q

example of allelic heterogeneity

A

beta-thalassemia

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22
Q

Genetic terms: heteroplasmy

A

presence of both normal and mutated mitochondrial DNA (mtDNA), resulting in variable expression in mitochondrially inherited diseases

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23
Q

Genetic terms: Uniparental disomy

A

offspring receive 2 copies of chromosome from 1 parent, and no copies from the other

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24
Q

Uniparental Disomy: Heterodisomy vs. Isodisomy

A

Heterodisomy (heterozygous) indicates a meiosis I error
Isodisomy (homozygous) indicates a meiosis II error or postzygotic chromosomal duplication of one pair of chromosomes and the loss of the other original pair.

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25
Q

when to consider uniparental Disomy?

A

when an individual is manifesting a recessive disorder when only one parent is a carrier
ie: prader-willi and angleman syndromes,

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26
Q

Hardy-Weinberg equation

A

p^2 + 2pq +q^2 =1
and
p + q = 1

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27
Q

In the Hardy-Weinberg equation p^2, q^2, and 2pq represent the frequency of what?

A 
p^2 = frequency of homozygosity for allele A
q^2 = frequency of homozygosity for allele a
2pq = frequency of heterozygosity
28
Q

Hardy-Weinberg frequency of an X-linked recessive disease in males and in females

A 
males = q
females = q^2
29
Q

Hardy-Weinberg Law assumptions include…(4)

A
  1. no mutations occurring at the locus
  2. natural selection is not occurring
  3. completely random mating
  4. no net migration
30
Q

Genetic terms: imprinting

A

one gene copy is silenced by methylation, and only the other copy is expressed&raquo_space;> parent-of-origin effects

31
Q

Prader-Willi Syndrome: what imprinting nonsense is going on?

A

maternally derived genes are silenced (imprinted)

disease occurs when the paternal allele on chr 15 is deleted or mutated.

32
Q

Prader-Willi Syndrome: manifestations

A 
hyperphagia
obesity
intellectual disability
hypogonadism
hypotonia
33
Q

Prader-Willi Syndrome: 25% of cases are due to ___

A

maternal uniparental disomy

34
Q

Angelman Syndrome: what imprinting nonsense is going on?

A

paternally derived UBE3A gene is silenced (imprinted)

disease occurs when maternal allele on chr 15 is mutated or deleted

35
Q

Angelman Syndrome: manifestations

A 
"happy puppet"
inappropriate laughter
seizures
ataxia
severe intellectual disability
36
Q

Angelman Syndrome: 5% of cases are due to ___

A

paternal uniparental disomy

37
Q

Modes of inheritance: AD

A

defects in structural genes
many generations
males and females

38
Q

Modes of inheritance: AR

A

enzyme deficiencies
one generation
commonly more severe than AD disorders

39
Q

Modes of inheritance: X linked recessive

A

sones of heterozygous mothers have 50% chance of being affected
no male-to-male transmission
skips generations
females must be homozygous to be affected

40
Q

Modes of inheritance: X-linked dominant

A

transmitted through both parents
mothers give to 50% of sons and daughters.
fathers give to all daughters but no sons

41
Q

x linked dominant examples

A

hypophosphatemic rickets
fragile X syndrome
alport syndrome

42
Q

Modes of inheritance: mitochondrial

A

transmitted only through the mom
all offspring of affected females may show signs of disease
can have variable expression bc heteroplasmy

43
Q

most common lethal genetic disease in white people

A

cystic fibrosis

44
Q

females w/ ___ are more likely to have an x-linked recessive disorder

A

Turner Syndrome (XO)

45
Q

what is the largest protein-coding human gene?

A

dystrophin

46
Q

rett syndrome

A 
sproadic, mostly girls
mutation of MECP2 on chr X
sx: 
-regression of motor, verbal, and cognitive abilities 
-ataxia
-seizures
-growth failure
-sterotyped hand wringing
47
Q

Fragile X syndrome: inheretance

A

x linked dominant

48
Q

Fragile X syndrome: mutation

A

trinucleotide repeat in FMR1

49
Q

what is the most common cause of inherited intellectual disability?

A

Fragile X syndrome

50
Q

Fragile X syndrome: findings

A

post-pubertal macroochidism
long face with large jaw, large everted ears
autism
mitral valve prolapse

51
Q

Fragile X syndrome: what trinucleotide, and when does expansion occur?

A

CGG, occurs during oogenesis

52
Q

trinucleotide repeat in huntingtons

A

CAG

53
Q

trinucleotide repeat in myotonic dystrophy

A

CTG

54
Q

trinucleotide repeat in fragile X

A

CGG

55
Q

trinucleotide repeat in friedrich ataxia

A

GAA

56
Q

Name for trisomy 21

A

Down Syndrome

57
Q

Name for trisomy 18

A

Edwards syndrome

58
Q

Name for trisomy 13

A

Patau syndrome

59
Q

the 5 A’s of down syndrome

A 
advanced maternal age
atresia (duodenal)
Atrioventricular septal defect
alzheimers (early onset)
AML/ALL
60
Q

Edwards Syndrome: findings

A

Prominent occiput, rocker bottom feet, intellectual disabilities, nondisjunction, clenched fists w/ overlapping fingers, low set ears, micrognathia (small jaw) congenital heart disease

61
Q

Patau Syndrome: findings

A

Severe intellectual disability, rocker bottom feet, microphthalmia, microcephaly, cleft lip/palate, holoprosencephaly, polydactyly, cutis aplasia, congenital heart disease, PKD

62
Q

Cri-du-chat syndrome: mutation

A

congenital deletion of 5p

63
Q

Cri-du-chat syndrome: findings

A

microcephaly, mod-severe intellectual disability, high pitched crying that sounds like meowing, epicentral folds, cardiac abnormalities (VSD)

64
Q

Williams syndrome: mutation

A

micro deletion of 7q, deleted region includes elastin gene

65
Q

Williams syndrome: findings

A

Distinctive “elfin” facies, intellectual disabilities, hypercalcemia, well developed verbal skills, extreme friendliness with strangers, cardiovascular problems

66
Q

Digeorge vs velocardiofacial syndrome

A

both 22q11 deletion&raquo_space; CATCH 22
DiGeorge: thymic, parathyroid, and cardiac defects
Velocardiofacial: palate, facial, and cardiac defects

Board Review (11 decks)

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