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Step 1 Prep > Genetics > Flashcards

Genetics Flashcards

1
Q

Who are bi-cyclic: purines or pyrimidines?

A

Purines [A, G]

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2
Q

Phosphodiester bonds are catalyzed by which enzymes?

A

DNA/RNA ; DNA ligase

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3
Q

Which bases hydrogen bond 3 times vs 2? AT or GC

A

GC bonds 3x H

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4
Q

DNA exterior is + or - charged at physiological pH?

A

Negative

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5
Q

If a sample of DNA contains 35% adenine, what % of other nucleotides? What is this rule called?

A

35% T
15% C; 15% G
* Chargaff’s rules

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6
Q

Which is more unstable: RNA or DNA

A

RNA [used within hours to days]; bacterial RNA used and degraded within minutes

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7
Q

Post-transcriptional modifications include:

A
  1. Addition of 5’ cap, 3’ poly-A tail

2. Splicing of introns out

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8
Q

Capping of eukaryotic mRNA occurs by addition of ___________. What is the function of the cap?

A

7-methyl-guanosine

* Regulates export out of nucleus; translation; slows degradation

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9
Q

What are the functions of the 3’ mRNA poly-A tail?

A

Increases t1/2 by protecting it from enzymatic degradation in the cytoplasm; interacts with 5’ cap which aids in export of mRNA from nucleus

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10
Q

Splicing removes introns or exons? What is another name for a splice site? 5’ donor always has; 3’ acceptor has:

A

Introns; consensus sequence
5’: GU
3’ AG

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11
Q

T/F 60% of human genes are spliced in alternative ways to allow for production of different set of mRNA.

A

True: altered function, tissue-specific isoforms, alternative intracellular localization, membrane-bound and soluble forms

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12
Q

What is the classiscal example of mRNA editing?

A

Editing of apolipoprotein-B mRNA. Liver = B-100; Intestine: B-48

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13
Q

What comes first: donor or acceptor site when considering splicing of introns?

A

Donor followed by acceptor

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14
Q

Differentiate between RNA pol 1, 2, 3

A

RNA pol 1: rRNA [most abundant]
RNA pol 2: mRNA
RNA pol 3: tRNA

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15
Q

Alpha-amanatin [poison deathcap mushroom] inhibits which RNA polymerase?

A

RNA pol 2

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16
Q

Do promotors contact RNA pol 2 directly?

A

No, they use transcription factors

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17
Q

What are several examples of sequences within eukaryotic promotor regions that are recognized by RNA polymerase 2?

A

CAAT box; TATA box

* Basal transcription machinery also

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18
Q

T/F Enhancer sequences may be very far away from transcription start sites. What do enhancers bind to?

A

True; activators

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19
Q

Molecular mechanism of DMD vs. BMD

A

DMD: deletion/stop codon (frame-shift)
BMD: missense (in frame)

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20
Q

What is the function of dystrophin protein?

A

Links the actin cytoskeleton with protein complexes that are associated with sarcolemma membrane; provides cell integrity.

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21
Q

T/F PCR may not detect heterozygotes. What is a way around this?

A

True; multiplex ligation dependent probe amplication PCR.

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22
Q

How can females display DMD symptoms?

A

In the manifesting heterozygote female, there are tissues that are healthy while others are badly affected; functional mosaicism

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23
Q

The most common lethal inherited disease in Caucasians?

A

Cystic fibrosis

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24
Q

The principal cause of death in CF

A

End stage lung disease

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25
Q

In the chloride sweat test, what drug is used to stmulate the sweat glands?

A

Pilocarpine (muscarinic agonist)

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26
Q

The COL1A1 gene mutation can lead to…

A

OI

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27
Q

Mutations in SERPINA1 gene lead to…

A

A1AT (Serine protease inhibitor); loss of neutrophil elastase inhibition

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28
Q

The characteristic genetic principle demonstrated through triplet repeat expansion disorders is:

A

Anticipation [age of onset and severity becomes earlier in subsequent generations]

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29
Q

Repeat sequence: Huntington disease

A

CAG [protein coding]

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30
Q

Repeat sequence: Fragile X Syndrome

A

CGG

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31
Q

Repeat sequence & inheritance of: Myotonic dystrophy

A

CTG [AD]

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32
Q

Is there a gain of function mutation associated with Huntington disease?

A

Yes: polyglutamine repeat

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33
Q

The CAG repeat expansion occurs during male gametogenesis in this disorder. This is an example of meiotic drive, whereby germ cells that contain expanded repeats can have a selective advantage.

A

Huntington disease (in myotonic dystrophy, the CTG repeat can also lead to meiotic drive).

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34
Q

Intellectual disability, learning difficulties, elongated face, low muscle tone, flat feet and macroorchidism

A

Fragile X Syndrome (X-linked Dominant inheritance) CGG

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35
Q

Name the major triplet repeat expansion disorders and their triplets.

A

Fragile X: CGG
Huntington: CAG
MD: CTG

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36
Q

What is an example of an X-linked dominant mutation? This condition leads to methylation mediated epigenetic gene silencing

A

Fragile X syndrome

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37
Q

Reduced expression of the FMR1 gene

A

Fragile X syndrome

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38
Q

T/F Maternal anticipation results in highest triplet expansions in myotonic dystrophy

A

T

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39
Q

DMPK mutation results in

A

Myotonic dystrophy (CTG repeat)

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40
Q

Lack of muscle coordination during voluntary movments, vision impairment, scoliosis, DM, heart disorders

A

Freidreich ataxia [frataxin gene]; involves mitochondrial iron metabolism that leads to the formation of heterochromatin

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41
Q

Anencephaly refers to the congenital absence of the cranial vault. It is a sysraphic anomaly of neural tube closure that results from an injury to the fetus when?

A

During 23-26th day of gestation

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42
Q

Disfiguring neurofibromas, cafe au Lait spots, pigmented lesions of iris is due to the loss of which tumor supressor gene?

A

NF-1: GTPase-activating protein

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43
Q

What is one of the major complications of NF1?

A

Neurofibrosarcoma; meningioma, optic glioma, pheochromcytoma

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44
Q

The hallmark of this lysosomal storage disease is the presence of lipid-laden macrophages [wrinkled tissue paper] that are characteristically present in the red pulp of the spleen, liver sinusoids, lymph nodes, lungs, bone marrow.

A

Gaucher disease [also bone pain]

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45
Q

Anasarca in an erythroblastalis fetalis baby is 2/2

A

CHF

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46
Q

Which serum Ig crosses the placenta?

A

IgG

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47
Q

A 19-year-old man is referred to a neurologist because of failing eyesight and progressive muscle weakness. The
neurologist takes a history and finds that several of the patient’s male and female relatives have similar symptoms. His
mother, her brother and sister, and two of the aunt’s children are affected, but the uncle’s children are not. What is the inheritance pattern?

A

Mitochondrial

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48
Q

Androgen insensitivity is also called

A

Testicular feminization

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49
Q

Gene sequence:
5’—-TAAGCCAATTGG—-3’

Sequence of the primer for PCR or ASO probe?

A

5‟—-CCAATTGGCTTA—-3‟

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50
Q

T/F Epigenetic modifications such as methylation regulate the rate at which transcription occurs

A

True

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51
Q

Give serveral examples of extragenic DNA.

A

Tandem repeat
* Satellite, minisatellite (telomeric, hypervariable), microsatelliite
Interspersed

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52
Q

Where is the highest gene density in DNA?

A

Sub-telomeric

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53
Q

Are heterochromatic and centromeric regions of DNA coding or non-coding?

A

Non-coding

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54
Q

Nuclear DNA can be divided into what 2 types of genes

A
  1. Single copy: single protein
  2. Multigene families
    - Classic: HOX [high homology]
    - Superfamilies: HLA, TCR [limited homology]
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55
Q

What % of DNA is protein coding?

A

<2%

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56
Q

Variable number of tandem repeats (VNTR) and short tandem repeats (STR) are inherited in what fashion?

A

Co-dominant [used for DNA fingerprinting]

57
Q

Minisatellite vs. Microsatellite

A

Mini: Telomeric; hypervariable (6NT)
Micro: Very short sequences (2NT); short tandem repeat – trinucleotide expansion diseases

58
Q

Trinucleotide repeat expansion diseases are associated with which aspect of a chromosome?

A

Microsatellite

59
Q

What are SINES and LINES?

A

Short and Long interspersed nuclear elements; some have RT activity; responsible for many of the mutations that have arisen 2/2 unequal crossover during meiosis.

60
Q

Short arm vs. Long Arm of a chromsome

A

P arm: short arm

Q arm: long arm

61
Q

A research geneticist has identified a
tetranucleotide repeat polymorphic marker, that
is linked to an autosomal dominant disorder in a
family. This marker belongs to the class of:

A

Microsatellite DNA

62
Q

T/F Genes are generally absent in the telomeres and centromere.

A

True

63
Q

Differentiate between: metacentric, submetacentric, and acrocentric chromosomes.

A

Metacentric: p = q
Submetacentric: p shorter than q

Acrocentric: p contains very little information

64
Q

What types of chromosomes are involved in Robertsonian translocations?

A

Acrocentric chromosomes: p arm contains very little genetic information

65
Q

Karyotyping is viewed during what phase of the cell cycle?

A

Metaphase

66
Q

When both the chromosomes of the pair are derived from the same parent, it is said to be called

A

Uniparental disomy

67
Q

T/F X-inactivation is fixed: the same X chromosome is inactivated in all the descendants of the cell.

A

True

68
Q

X-inactivation is regulated by a region on the chromosome called..

A

X-inactivation center: XIST

69
Q

Methylation of _____________ bases, also called _______ islands, close to the promotor, results in transcriptional repression.

A

Cytosine bases; CG islands

70
Q

The process of ___________ is similar to X-inactivation, in that the imprinted gene is methylated and transcriptionally silenced

A

Imprinting

71
Q

Locus of a gene

A

Refers to its location on a chromosome

72
Q

Maximum time in the cell cycle is spent in: interphase or mitosis

A

Interphase

73
Q

Give examples of labile, stable and permanent cells

A

Labile: Skin, GIT, epithelial
Stable: Liver
Permanent: Neuron, cardiac muscle

74
Q

The important G1-S checkpoint proteins

A

p53 & Rb

75
Q

What molecules regulate the entry of cells into the various phases of the cell cycle?

A

Cyclins

76
Q

What phase of the cell cycle? Nuclear envelope dissolves. Mitotic spindle forms, chromosomes start condensing and become visible; chromosomes start binding to the spindle

A

Prophase

77
Q

What phase of the cell cycle? Separation of sister chromatids

A

Anaphase

78
Q

What are the major events of meiosis 1 & 2?

A

1: Homologous chromosomes separate
2: Sister chromatids separate

79
Q

During meiosis 1 non-disjunction…

A

Homologs do not separate

80
Q

During meiosis 2 non-disjunction…

A

Sister chromatids do not separate

81
Q

Male vs. Female: When does gametogenesis commence?

A

Male: Puberty
Female: Early embryonic life

82
Q

In a female, oocytes are arrested in… until ovulation.

A

Prophase I

83
Q

T/F There is a higher risk of maternal non-disjunction in meiosis, resulting in a higher risk of trisomy.

A

T

84
Q

T/F A higher paternal age can result in the development of new dominant single gene mutations.

A

T

85
Q

Locus vs. Allele

A

Locus: location of a gene
Allele: one of the alternative forms of a gene that occur at a locus

86
Q

AD disorders manifest in the homo/hetero-zygous state?

A

Heterozygous

87
Q

Is male-to-male inheritance seen in AD conditions?

A

Yes

88
Q

Inheritance: Familial hypercholesterolemia (LDL R deficiency)

A

AD

89
Q

Inheritance: Huntington disease

A

AD

90
Q

Inheritance: Myotonic dystrophy

A

AD

91
Q

Inheritance: Marfan syndrome

A

AD

92
Q

Inheritance: OI

A

AD

93
Q

Inheritance: Achondroplasia

A

AD

94
Q

Inheritance: NF-1

A

AD

95
Q

Inheritance: Acute intermittent porphyria

A

AD

96
Q

AD mutation in the DMPK gene; most pleiotropic phenotype of all unstable 3xrepeat disorders; characterized by wasting of muscles, cataracts, heart conduction defects, endocrine defects, myotonia

A

Myotonic dystrophy

97
Q

AD FGFR3 mutation

A

Achondroplasia

98
Q

NF-1 is caused by different mutations in the NF-1 gene. What is this called? Locus or Allelic heterogeneity

A

Allelic heterogeneity

99
Q

Horizontal inheritance: AR or AD

A

AR

100
Q

In AR sibships, what proportion of non-affected siblings are carriers?

A

2/3

101
Q

Inheritance: CF

A

AR

102
Q

Inheritance: SCA

A

AR

103
Q

Inheritance: PKU

A

AR

104
Q

Inheritance: Tay Sachs

A

AR

105
Q

Inheritance: Congenital deafness

A

AR

106
Q

Inheritance: Hemochromatosis

A

AR

107
Q

The most common mutation of the HFE gene?

A

C282Y mutation

108
Q

What are several reasons for pseudo-autosomal dominant inheritance?

A

High carrier frequency, birth of an affected child to an affected individual, consanguinity

109
Q

Inheritance pattern of blood types

A

Co-dominance

110
Q

Is male-to-male inheritance seen in X-linked recessive disorders?

A

No

111
Q

Inheritance: Duchenne & Becker muscular dystrophy

A

X-linked recessive

112
Q

Inheritance: G6PD deficiency

A

X-linked recessive

113
Q

Inheritance: Hemophilia A & B

A

X-linked recessive

114
Q

Inheritance: Lesch-Nyhan syndrome

A

X-linked recessive

115
Q

Inheritance: Red-green color blindness

A

X-linked recessive

116
Q

Several possible explanations for a manifesting heterozygote in an X-linked recessive disorder

A
  1. Skewed inactivation
  2. Presence of two mutant copies (dad + mom)
  3. Female with only copy of the X-chromosome
117
Q

In X-linked dominant disorders, there is a preponderance of females compared to males.

A

Females; male transmits the disease to all his daughters; none of his sons are affected

118
Q

Inheritance: Vitamin D resistant rickets

A

X-linked Dominant

119
Q

Inheritance: Incontinentia pigmenti

A

X-linked Dominant

120
Q

Y-linked inheritance genes are usually not passed on b/c they cause sterility. 2 Examples of Y-linked inheritance

A

Mutations in SRY gene; H-Y histocompatibility Ag

121
Q

Hemochromatosis is more severe in males. This is known as:

A

Variable expression

122
Q

Xeroderma pigmentosum is more severe in individuals exposed more frequently to UV radiation. This is known as:

A

Variable expression

123
Q

A disease causing a mutation that affects multiple organ systems, i.e. Marfan syndrome or OI is known as

A

Pleiotrophic

124
Q

Pleiotrophic disease

A

One mutation affects multiple organ systems: Marfan, OI

125
Q

Mutations on chromosome 17 or 7 can lead to the manifestations of osteogenesis imperfecta. This is known as: ________. Other examples include: CMT disease, sensorineural hearing, retinitis pigmentosa

A

Locus heterogeneity.

126
Q

T/F Allelic heterogeneity can lead to compound heterozygosity.

A

True

127
Q

A 23 year old female is pregnant and has come for genetic
counseling. Her father (50 years) is diagnosed to have
Huntington’s disease. What is her risk of transmitting the mutant
gene to her child?

A

50% * 50% = 25%

128
Q

In Huntington’s disease, the disorder is generally more severe if transmitted from the father

A

True

129
Q

The severity of mitochondrial disorders can vary in individuals with the disorder. This is due to the phenomenon of:

A

Heteroplasmy

130
Q

Inheritance: Leber hereditary optic neuropathy

A

Mitochondrial

131
Q

Inheritance: MELAS / Mitochondrial encephalopathy, lactic acidosis, stroke

A

Mitochondrial

132
Q

Inheritance: MERRF / Myoclonic epilepsy with ragged red muscle fibers

A

Mitochondrial

133
Q

Triplet repeat disoders: Promoter, Intron, Coding, 3’ end

A

Promoter: Fragile X
Intron: Friedrich ataxia
Coding: Huntington
3’: Myotonic dystrophy

134
Q

Triplet repeat of FMR1 gene

A

Fragile X syndrome

135
Q

Deletion of paternal 15q11-13 (absence of SNRPN) results in

A

Prader-Willi syndrome [obese, mental delay, underdeveloped genitalia]
* Typically, the chromosome is imprinted in the mother

136
Q

Describe the phenomenon of trisomy rescue and its relationship to uniparental disomy

A

You actually have an extra copy of the chromosome

137
Q

Deletion of maternal 15q11-13 (absence of UBE3A) results in

A

Angelman syndrome: Happy puppet syndrome

138
Q

Mutations in 2 genes are additive and necessary to produce the disoder. One example of this type of digenic inheritance is…

A

Retinitis pigmentosa

Step 1 Prep (15 decks)

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