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Foundation of Medical Genetics > Midterm > Flashcards

Midterm Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Single-gene disease inheritance depends on

A
  1. where the gene is located (autosome v. sex chromosomes)
  2. how the phenotype is express (recessive v. dominant)
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2
Q

Can be observed in multiple generations within a pedigree

A

Autosomal Dominant

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3
Q

Law of Addition

A

add the probabilities of two mutually exclusive events to get probability of either event occurring
“or”

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4
Q

Law of Multiplication

A

multiply probabilities of independent events to get the probability of. more than one occurring
“and”

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5
Q

Penetrance

A

probability that a mutant allele will have any phenotypic expression

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6
Q

incomplete penetrance

A

when individuals with a disease causing genotype completely fail to express the phenotype

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7
Q

expressivity

A

degree of severity of a phenotype- the degree to which the phenotype is expressed

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8
Q

variable expressivity

A

when severity of a disease between individuals with the same genotype varies

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9
Q

Carrier frequency

A

the proportion of individuals in a population who are carriers for a genetic condition

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10
Q

Example of X-linked Recessive

A

red-green color blindness

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11
Q

Compound heterozygous

A

The presence of two different mutated alleles at a particular gene locus

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12
Q

gene

A

gene is a basic unit of heredity and the molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA

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13
Q

allele

A

one specific variant for a given polymorphism

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14
Q

Skewed X-inactivation

A

due to random chance or reduced survival of cells expressing a particular X chromosome

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15
Q

Pseudoautosomal inheritance

A

Genes on the Y-chromosome are sometimes passed to daughters, and genes on the X-chromosome are sometimes passed from fathers to their sons. This is possible because the X- and Y-chromosomes share regions of sequence identity, and these regions undergo recombination during male meiosis.

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16
Q

Example of X-linked dominant w/ Male Lethality

A

Incontinetia pigmenti
focal dermal hyperplasia

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17
Q

Possible living offspring of an affected female with x-linked dominant w/ male lethality

A

affected female, unaffected female, unaffected male

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18
Q

Examples of X-linked dominant with male sparing

A

craniofacial dysplasia
epilepsy w/ intellectual disability

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19
Q

Effects of x linked dominant w/ male sparing on females v. males

A

heterozygous females are affected, males are not or minimally affected, unaffected male leads to affected female transmission

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20
Q

Mosaicism

A

Presence of at least two different cell lineages that contain genetic differences but are derived from the same zygote

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21
Q

confined placental mosaicism

A

cells in the placenta differ from cells in the embryo

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22
Q

somatic mosaicism

A

differing cell populations within somatic tissue, but gametes identical

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23
Q

germline mosaicism

A

differing cells only in gametes
example: mutation in FBN1 (Marfan)

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24
Q

Nuerofibromstosis Type 1 (NF1)

A

AD condition caused by mutations in NF1 gene (tumor suppressor) 50/50 de nov/inherited

phenotypes: Cafe au lait spots, linch nodules, nerve tumors, axillary freckling, optic glioma, plexiform neurofibromas

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25
Q

Genomic Imprinting

A

A process of silencing genes through DNA methylation. The repressed allele is methylated, while the active allele is unmethylated.

Which copy is active depends on the parent of origin: some genes are normally active only when they are inherited from a person’s father; others are active only when inherited from a person’s mother

Examples include Prader-Willi and Angelman syndromes (the first examples of genomic imprinting in humans).

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26
Q

Prader-Willi Syndrome

A

Parent of origin effects- loss of maternally expressed genes
incidence 1/20000
characterized by severe hypotonia and feeding difficulties in the neonatal period, obesity, developmental delay

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27
Q

Angelman Syndrome

A

parent of origin effects- loss of paternally expressed genes
incidence 1/15000
characterized by seizure disorder, ataxic gait, happy appearance w/ inappropriate laughter

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28
Q

unstable repeat expansions

A

dynamic mutations that change from generation to generation
larger repeat= increased severity
i.e. huntingtons, fragile X, myotonic dystrophy

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29
Q

Huntington Disease

A

progressive neurologic condition of motor, cognitive and psychiatric impairment
caused by CAG repeats
normal <26
intermediate 27-35
HD causing- >36

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30
Q

anticipation

A

increasing disease severity or decreasing age of onset is observed in successive generations
i.e. HD, myotonic dystrophy

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31
Q

mitochondria inheritance have three unique features

A

maternal inheritance, replicative segregation, homoplasmy/ heteroplasmy

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32
Q

heteroplasmy

A

differences in the mtDNA between the different mitochondria within a cell

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33
Q

allelic heterogeneity

A

different mutation in a gene may produce the same phenotype
i.e. >1000 mutations cause CF

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34
Q

locus hetergeneity

A

mutations in different genes may cause the same phenotype

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35
Q

clinical or phenotypic heterogeneity

A

different mutations in a gene may result in different phenotypes

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36
Q

euploidy

A

abnormal copies in all chromosomes

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37
Q

aneuploidy

A

abnormal copies iof a single chromosome

38
Q

uniparental disomy

A

disomic state where both chromosomes are inherited from the same parent

39
Q

isodisomy

A

chromsomes inherited from sister chromatids

40
Q

heterodisomy

A

inheritance of both homologs from one parent

41
Q

marker chromosomes

A

is a rearranged small chromosome whose genetic origin is unknown based on its G-banded chromosome morphology

can contain material from one or both chromosome arms

called ring chromosomes when they lack telomeres

42
Q

isochromosomes

A

arm of one chromosome is duplicated
creates a mirrored chromosome, with both arms containing duplicated genetic material
results in trisomy of the duplicated arm and monosomy of the non duplicated arm

43
Q

reciprocal translocation

A

recombination between nonhomologous chromosomes
can be balanced or unbalanced
balanced typically have no effect
high risk for unbalanced gametes

44
Q

robertsonian translocations

A

fusion of two eccentric chromosomes near the centromere
loss of short arms of the fused chromosomes

45
Q

causes of Down syndrome

A

95% trisomy 21
4% robertsonian translocation

46
Q

causes of turner syndrome

A

50% 45,X
25% structural abnormality of X (isochromsome)
25% 45, X mosaicism

47
Q

causes of turner syndrome

A

50% 45,X
25% structural abnormality of X (isochromsome)
25% 45, X mosaicism

48
Q

how can we identify chromosomal alterations

A

karyotype
FISH
Microarray

49
Q

karyotype

A

used to identify microscopic changes in chromosomes number or configuration

50
Q

FISH

A

can identify submicroscopic changes in chromosomes structure and rearrangements

51
Q

microarray

A

identify submicroscopic changes in copy number

52
Q

population

A

group of interbreeding individuals of the same species sharing a common geographic area

53
Q

Causes of allele frequency change

A

bottleneck events, mutations, natural selection, migration, nonrandom mating,

54
Q

Assumptions of Hardy Weinberg

A

random mating, no natural selection,, large population size, no migration or gene flow between populations

55
Q

How similar are humans to each other…

A

99.9%

56
Q

linkage disequilibrium

A

the nonrandom association of alleles at different loci (on the same chromosome)

57
Q

haplotypes

A

a set of DNA variants along a single chromosome that tend to be inherited together.

58
Q

who discovered structure of DNA

A

Maurice Wilkins + Rosalind Franklin
James Watson and Francis Crick

59
Q

How many genes in human genome?

A

25,000

60
Q

How many basepairs per haploid in the human genome?

A

3.2 billion

61
Q

How many basepairs per haploid in the human genome?

A

3.2 billion

62
Q

genome

A

the entire genetic make up of an organism

63
Q

polymorphism

A

any DNA sequence variation

64
Q

genotype

A

the combined alleles at a specific locus

65
Q

haplotype

A

alleles from different loci occur on the same chromosome

66
Q

phenotype

A

the observable or measurable trait

67
Q

Single nucleotide polymorphisms

A

single base changes

68
Q

synonymous mutation

A

change in one DNA base pair without changing amino acid sequence
AGG->AGA

69
Q

missense mutation

A

change in one DNA base pair that results in one amino acid change
CCT->CTT

70
Q

nonsense mutation

A

change in one DNA base pair that results in STOP codon and shortened protein
CAG->TAG

71
Q

frameshift mutation

A

add or remove a piece of DNA base pairs, not multiple of 3 base pairs

72
Q

repeat expansion

A

repeat a piece of DNA base pair(s) a number of times

73
Q

What can we tell from Hardy Weinberg Equilibrium

A

whether or not a species is evolving, allele frequencies are changing

74
Q

Central Dogma

A

DNA to RNA transcript to mature mRNA to protein

75
Q

mRNA 5’ capping

A

stabilizes transcript

76
Q

Promoters

A

upstream (5’) of the transcription start site

77
Q

Eukaryotic Transcription

A

DNA is in a loose configuration

general transcription factors must bind to promoter sequence prior to RNA polymerase

Specific transcription factors bind to enhancer sequences to regulate transcription

78
Q

RNA processing

A

must happened for RNA to be functional
1. 5’ capping
2. exon splicing
3. poly-A addition

79
Q

mRNA splicing

A

removes introns of gene, unique to eukaryotes, allows for mutations to occur with less chance of a detrimental effect, allows for more complex proteins to be created

80
Q

mRNA Polyadenylation

A

sequence indicates cleavage of the mRNA about 20 nucleotides downstream

81
Q

P site in Translation

A

Peptidyl site, binds to the tRNA holding the growing polypeptide chain of amino acids

82
Q

A site in Translation

A

acceptor site; binds to the aminoacyl tRNA, which holds the new amino acid to be added to the polypeptide chain

83
Q

E site in Translation

A

exit site, serves as a threshold, the final transitory step before a tRNA now bereft of its amino acid is let go by the ribosome

84
Q

What two components are needed for effective gene expression regulation

A
  1. cis-acting elements (DNA consensus sequences)
  2. Tran-acting factors (Gene regulatory proteins)
85
Q

Histone acetylation

A

leads to gene activation

86
Q

positional cloning

A

identifies a disease gene based solely on its position in the genome, independent of its function

combines linkage analysis with physical mapping

can identify a previously unknown gene or regulatory sequence

87
Q

Cystic Fibrosis

A

AR, Gene CFTR; one gene many mutations

88
Q

Reduced genetic variation is observed

A

with distance from Africa

89
Q

Which SNPs are functionally important?

A

no clue, were not sure which SNPs have functional relevance

90
Q

DNA Structure

A

phosphodiester backbone, deoxyribose sugar, nitrogenous bases

Foundation of Medical Genetics (1 decks)

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