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Block 6 > Genomic Imprinting > Flashcards

Genomic Imprinting Flashcards

1
Q

What is a microdeletion?

A

small deletion in a gene that results in a small partial monosomy

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2
Q

What is genomic imbalance syndrome?

A

a disease phenotype associated with deletion of multiple adjacent genes in critical regions

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3
Q

What is a critical region?

A

a particular chromosome segment; associated with a specific abnormal phenotype when microdeletions are present

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4
Q

What is a low copy repeat?

A

repeat dispersed throughout genome that is linked with abnormal phenotypes when microdeletions are present

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5
Q

What is contiguous gene syndrome?

A

abnormal phenotype caused by microdeletion/duplication of several genes in close proximity

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6
Q

What is a microduplication?

A

small partial trisomy in a certain genomic region

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7
Q

What is a subtelomeric rearrangement?

A

terminal rearrangement, most often involving microdeletions of telomeres

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8
Q

What is segmental aneuploidy syndrome?

A

a subtype of contiguous gene syndrome that recurs due to non-allelic homologous recombination between low-copy repeats

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9
Q

What is the Prader-Willi syndrome phenotype?

A

infancy hypotonia, childhood hyperphagia and obesity, mental retardation and hypogonadism

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10
Q

What is the genetic cause of Prader-Willi syndrome?

A

C15 microdeletion caused by unequal crossing over of low-copy repeats at breakpoint (3 possible BPs) when homologous pairs are misaligned

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11
Q

What are two illegitimate recombinations of genetic segments located between low-copy repeats?

A
  1. direct repeats: direct deletion or duplication

2. inverted repeats: flipped orientation

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12
Q

What’s the difference between benign and pathogenic CNVs?

A

benign CNVs are normal an dispersed in the genome, whereas pathogenic CNVs will encompass the critical region of a gene and cause abnormal phenotype

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13
Q

What are the 3 ways to diagnose a segmental aneuploidy?

A
  1. standard karyotype
  2. FISH
  3. aCGH/CMA (comparative genomic hybridization/chromosomal microarray)
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14
Q

How does FISH detect a microdeletion?

A

based on clinical suspicion, send in probes for critical region; if 2 signals, it’s normal, if 1 signal there’s a microdeletion

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15
Q

What is a CMA/aCGH and what does it do?

A

assay to examine entire genome for regions of imbalance; confirms aneuploidy with result of patient:control ratio

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16
Q

Order these from least severe (1) to most severe (5): point mutation, structural abnormality, large structural abnormality, large CNV, small CNV

A
  1. SNP/point mutation
  2. small CNV
  3. large CNV
  4. structural abnormality
  5. large structural abnormality
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17
Q

What is the most common outcome(s) of an SNP?

A

localized disease, or nothing

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18
Q

What is the most common outcome of a small CNV?

A

normal variation, normal phenotype

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19
Q

What is the most common outcome of a large CNV/microdeletion?

A

mild phenotype appearing later in childhood

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20
Q

What is the most common outcome of a structural abnormality?

A

partial monosomy/trisomy; severe phenotype

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21
Q

What is the most common outcome of a large structural abnormality?

A

lethal/miscarriage

22
Q

Crossing over of two misaligned segments leads to:

A

2 abnormal products. One duplication and one deletion.

23
Q

Can CMA detect a point mutation (I.e. one base pair deletion)?

A

No

24
Q

Can CMA detect balanced rearrangements?

A

No

25
Q

Is FISH a targeted analysis of the entire genome?

A

No, only for the target you are probing for.

26
Q

What is a common complicating factor of CMA testing for abnormalities?

A

Variations in CNVs

27
Q

Is imprinting reversible?

A

Yes

28
Q

DNA methylation is a common mechanism for epigenetic control of:

A

Gene expression

29
Q

Is it absolutely necessary to have a female and a male gene complement in an offspring?

A

Yes. You could NOT combine male/male or female/female genes and get a viable offspring

30
Q

True or false: imprinting is conserved from one generation to the next

A

False. Imprinting is reset during gametogenesis of each generation

31
Q

Prader-Willi syndrome is due to genes missing that normally come from the mother or father?

A

Father

32
Q

Angelman Syndrome is due to missing genes that usually come from the mother or father?

A

Mother

33
Q

Can uniparental disomy be caused by one nondisjunction?

A

No. UPD is caused by 2 independent nondisjunction events during gametogenesis and/or embryogenesis of a single individual

34
Q

Describe Trisomy Rescue

A

Error #1- meiotic nondisjunction causing trisomy at conception.
Error #2- mitotic nondisjunction (one cell, early in development) that restores normal chromosome number in a daughter cell

35
Q

Trisomy Rescue can lead to Uniparental Disomy (this child born with either Prader-Willi or Angelman Syndrome) because:

A

Start with two maternal or paternal copies of Ch15 in what should be a 1n gamete. Combine male-female gametes and you now have trisomy 15. A later mitotic nondisjunction early in embryonic development may leave either the single maternal or paternal Ch15 out of the daughter cell and restore 2n, but the lack of contribution from both parents causes PWS or AS.

36
Q

What is a syndrome?

A

clinical signs and symptoms that are related/correlated with a common underlying cause

37
Q

What is 22q11 deletion syndrome?

A

microdeletion of the 22q11 locus that results in DiGeorge syndrome, cardiac abnormalities, immune deficiencies, and other symptoms

38
Q

What “drives” misalignment leading to potential unequal crossing over?

A

low copy number repeats of which there are multiple homologous ones, which can align with the wrong sequential CNV

39
Q

What is Williams syndrome?

A

mild to moderate intellectual disability, cardiac anomaly, and distinctive facial appearance

40
Q

Why is FISH useful for the 22q11 microdeletion syndrome?

A

FISH is useful to confirm diagnosis

41
Q

What’s the individual utility of each test: karyotype, FISH, CMA

A

karyotype is cheap
FISH is specific
CMA is sensitive

42
Q

What is Angelman syndrome?

A

phenotype of spasticity and seizures, mental and growth retardation; caused by 15(q11q13) deletion (same as Prader Willi microdeletion)

43
Q

What is the difference between Prader Willi and Angelman syndrome?

A

PWS=paternal deletion

AS=maternal deletion

44
Q

What is imprinting?

A

an epigenetic process that determines the genes that are expressed/not expressed, depending on parental origin

45
Q

How many genes throughout the genome are subject to imprinting?

A

a finite number (as in, not all of them)

46
Q

What kind of imprints are present in gametes?

A

parent-specific, so the mother’s imprinting patterns will be relayed to all the eggs

47
Q

What are three ways to lack functional paternal contribution of chromosome 15 genes which leads to PWS?

A
  1. paternal microdeletion
  2. maternal uniparental disomy
  3. imprinting center mutation
48
Q

What are the causes of AS?

A
  1. maternal microdeletion
  2. paternal uniparental disomy
  3. imprinting center mutation
  4. UBE3A point mutations (familial)
  5. others that are unknown
49
Q

What is uniparental disomy (UPD) and why is it rare?

A

when 2 copies of a chromosome are inherited from one parent and 0 copies from the other parent; rare because you have to have two independent errors

50
Q

What is trisomy rescue?

A

meiotic nondisjunction causing trisomy at conception, followed by mitotic nondisjunction that restores the normal chromosome number in a cell; causes UPD

Block 6 (19 decks)

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