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Genetics Flashcards

1
Q

What is the term codominance?

A

It meas that both alleles contribute to the phenotype of the heterozygote

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2
Q

What are the examples of codominance?

A

Blood groups: A, B, AB

HLA groups

Alpha 1 anti trypsin

M allele: normal
Z allele: severely reduced
S: moderately reduced

Combo: MM: normal, ZZ: severely reduced, other combos make varying degrees

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3
Q

What is term variable expressivity?

A

Same genotype: varying phenotypes

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4
Q

What is the example of variable expressivity?

A

NF1

2 patients with neurofibromatosis type 1 may have varying disease severity

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5
Q

What is term incomplete penetrance?

A

Not all individuals with the mutant genotype: show the mutant phenotype

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6
Q

How to calculate incomplete penetrance?

A

% penetrance x probability of inheriting genotype= risk of expressing phenotype

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7
Q

What does 100% penetrance means?

A

That all the individuals express the phenotype with the mutant gene

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8
Q

What is the example of incomplete penetrance?

A

BRCA1 gene mutations do not always result in breast or ovarian cancer

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9
Q

What is the term pleiotropy?

A

One gene= multiple phenotypic effects

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10
Q

What is the example of pleiotropy?

A

Untreated PKU: light skin, intellectual disability, musty body odor

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11
Q

What is the term anticipation?

A

Increased severity or earlier onset of disease in suceeding generations

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12
Q

What is the example of anticipation?

A

huntington disease (trinucleotide repeat expansion)

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13
Q

What is loss of heterozygosity?

A

If a patient inherits or develops a mutated tumor supressor gene, the complementary allele must be mutated in order for cancer to develop

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14
Q

What is not true of oncogenes?

A

Loss of heterozygosity

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15
Q

What is the example of loss of heterozygosity?

A

Retinoblastoma

Hereditary form: Germ line mutation, passed down to offspring (one hit), somatic mutation in second copy
(Second hit)——-> multiple tumors, tumors at younger age

Two hit theory

Sporadic form: requires two somatic hits. And possibility of acquiring mutation in both alleles is rare———> single tumors, tumors at later stage

HNPCC, Li- Fraumeni syndrome

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16
Q

What is the term dominant negative mutation?

A

A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning

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17
Q

What is the example of dominant negative mutation?

A

Mutation in transcription factor, nonfuntioning mutant can still bind to dna and prevent the wild type transcription factor from binding

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18
Q

What is the term linkage disequilibrium?

A

Tendency for certain alleles at 2 linked loci to occur together more or less often than expected by chance

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19
Q

Is linkage disequilibrium measured in families or populations?

A

Population, varies in different populations

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20
Q

What is mosaicism?

A

It is the presence of genetically distint cell lines in the same individual

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21
Q

Somatic mutation is the mutation that arises from ____________ and propagates through___________

A

Mitotic errors after fertilisation

Multiple tissues or organs

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22
Q

Gonadal mosaicism is the mutation that only occurs in ________

A

Eggs or sperm cells

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23
Q

If the parent does not have the disease, we can suspect?

A

Gonadal mosaicism

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24
Q

What is the example of mosaicism?

A

Mc cune albright syndrome

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25
Q

McCune albright mutation is a mutation affecting_______

A

G protein signalling

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26
Q

McCune Albright syndrome patients have unilateral ________ and

A

Cafe au lait spots with ragged edges

Polyostotic fibrous dysplasia (bone is replaced by collagen and fibroblasts

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27
Q

What kind of endocrinopathy do patients with McCune Albright patients present with?

A

Precocious puberty

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28
Q

McCune Albright syndrome is lethal if mutation ________

A

Occurs before fertilisation, affects every cell. But survivable in patients with mosaicism

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29
Q

Locus heterogeneity is mutation at ________ and can produce a ________ phenotype

A

Different loci, similar

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30
Q

Allelic heterogeneity is mutation at ________ and can produce a ________ phenotype

A

In the same loci, same

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31
Q

Example of locus heterogeneity is?

A

Albinism

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32
Q

Example of allelic heterogeneity is?

A

Cystic fibrosis and b thalessemia

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33
Q

Heteroplasmy is presence of both mutated and normal _______, resulting in ________

A

Mtdsna

Variable expression in mitochrondrially inherited disease

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34
Q

Mtsdna is passed from?

A

Mother to all children

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35
Q

Uniparental disomy means offspring recieves ______ of chromosomes from _______ parent

A

2 copies of chromosomes

1 single parent

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36
Q

Heterodisomy results from

A

Meiotic error 1

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37
Q

Isodisomy results from?

A

Meiotic error 2

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38
Q

Uniparental is________

A

Euploid meaning correct number of chromosomes

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39
Q

Most occurences of uniparent disomy results in ________

A

Normal phenotype

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40
Q

Consider uniparental disomy in an individual manifesting a ________ disorder and only ________ is a _______

A

Recessive

1

Carrier

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41
Q

Examples of isoparental disomy are?

A

Prader willi, and angel man syndromes

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42
Q

Hardy weinberg is only applicable to a population if

A

No mutation occuring in the same locus

Large population

No intermixing

Natural selection is not occuring

No net migration

Natural Net intermixes with Large Mutation

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43
Q

Imprinting is _______ copy is _________ and only the copy __________

A

One
Silenced by methylation
Expressed

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44
Q

Imprinting has what origin?

A

Parent of origin effects

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45
Q

In prader willi syndrome _________ are silenced (imprinted). Disease occurs when the _______ allele is ________

A

Maternally derived genes

Paternal allele is deleted

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46
Q

Prader willi is associated with the mutation or deletion of ______ of _____origin?

A

15 chromosome

Paternal

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47
Q

How many number of cases are due to maternal uniparental disosmy (maternal non disjunction) in __________

A

25%

Prader willi

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48
Q

Prader willi is associated with _______

A 
Hyperphagia
Obesity 
Intellectual disability 
Hypogonadism 
Hypotonia
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49
Q

In AngelMan syndrome, the _________ is silenced and the _______ is deleted

A

Paternally derived UBE3A gene is silenced

Maternal allele is deleted or mutated

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50
Q

AngelMan syndrome is associated with mutation or deletion of _______ on the ________copy of chromosome_______

A

Ube3A
Maternal
15

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51
Q

How many number of cases are due to paternal uniparental disosmy (parental non disjunction) in __________

A

5%

AngelMan syndrome

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52
Q

What are the symptoms of AngelMan syndrome?

A

Inappropriate laughter (happy puppet) and seizures

Ataxia, and severe intellectual disability

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53
Q

What are the five modes of inheritance?

A

Autosomal dom, Autosomal rec
X linked dom, X linked rec
Mitochondrial

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54
Q

Autosomal dominant is due to __________ genes

A

Defects in structural

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55
Q

Is there skipping in dominant disorders?

A

No

56
Q

Are females affected in dominant disorders or males?

A

Both

57
Q

Is there male to male transmission in autosomal disorders?

A

Yes

58
Q

Which disorders are often pleiotropic and variably expressive between individuals?

A

Autosomal dominant

59
Q

What is crucial to aut dom disorders?

A

Family history

60
Q

One affected heterozygous parent, has on average how many affected children in autosomal dominant disorders?

A

1/2

    a      a

A Aa Aa

a aa. aa

61
Q

Autosomal recessive disorders are due to ________

A

Enzyme def

62
Q

Is there skipping in autosomal recessive disorders?

A

Yes

63
Q

With 2 carrier parents, how many children will be affected, carriers, and non affected

A

1/4
1/2
1/4

64
Q

Which is more severe, aut dom or aut recessive?

A

Aut rec

65
Q

Patients with _________ often present with symptoms in childhood

A

Aut rec

66
Q

In X linked recessive, sons of heterozygous mothers have _______ of being affected?

A

50 %
X Y
Xn Xn X XnY

X X X X Y

67
Q

Is there male to male transmission in x linked disorders?

A

No

68
Q

X linked recessive is more common in males or females?

A

Males

69
Q

Females in X linked recessive must be _________ to be affected?

A

Homozygous

70
Q

In X linked dominant, it is transmitted through ________ parent?

A

Both parents

71
Q

In x linked dominant, daughters and sons of heterozygous mothers have ______ of being affected?

A

50 %
X Y
Xn Xn X XnY

X X X X Y

72
Q

In which disorder do all fathers transmit the genes to all his daughters

A

X linked dominant

73
Q

What is the example of x linked dominant disorder?

A

Hypophosphatemic defect

74
Q

In vitamic D resistant, ________ in phosphate wasting, at _________ tubule

A

Increased

Proximal

75
Q

Vitamin d resistant disorder results in which type of presentation?

A

Rickets like

76
Q

Other examples of x linked dominant disorders are?

A

Fragile x and alport syndrome

77
Q

In mitochondrial inheritance, only _______ transmits the disease?

A

Mother

78
Q

Can all affected offspring show signs of disease in mitochondrial inherited disorder?

A

Yes

79
Q

Why is there variable expression in a population or even within a family in mitochondrial inheritance?

A

Heteroplasmy

80
Q

In mitochondrial myopathies, rare disorders, patients often present with __________

A

Myopathy
Lactic acidosis
Cns disease

81
Q

What is MELAS syndrome?

A

Mitochondrial encephalopathy
Lactic acidosis
Stroke like episodes secondary to failure in oxidative phosphorylation

82
Q

In MELAS syndrome, what does biopsy often shows?

A

Ragged red fibres, due to decreased mitochondria

83
Q

What is example of mitochondrial inherited disease

A

Leber hereditary optic neuropathy

84
Q

In Leber hereditary optic neuropathy __________ in optic nerve nuerons, there is permanent ___________ in teens/young adults

A

Cell death

Subacute bilateral vision loss

85
Q

In Leber hereditary optic neuropathy, how many males are affected?

A

90%

86
Q

Fragile X syndrome is what type of disorder?

A

X linked dominant

87
Q

In fragile X linked, there is __________ of ___________, which leads to __________ and ________ expression

A

Trinucleotide repeat, FMR1, hypermethylation, decreased

88
Q

Trinucleotide expansions occur due to __________

A

Slipped strand mispairing

89
Q

It is the most common cause of ___________ and second most common cause of _________ after down syndrome

A

Inherited intellectual disability, genetically associated mental deficiency after Down Syndrome

90
Q

What are the findings of Fragile X syndrome?

A

Post pubertal macroorchidism (enlarged testes), long face with large jaw and everted ears, autism, mitral valve prolapse

91
Q

Trinucleotide repeat expansions (CGG)n occurs in?

A

Oogensis

92
Q

What are the examples of trinucleotide repeat expansions?

A

Try hunting for my fragile cage free eggs

Trinucleotide huntington disease, myotonic dystrophy, fragile x syndrome, and Friedreich ataxia

93
Q

Trinucleotide repeat expansion diseases show genetic anticipation which means?

A

Severity increases, with the increased age of onset, and decreased sucessive generations

94
Q

Hungtington disease

Trinucleotide repeat (________)

Mode of inheritance (______)

Mnemonic ……

A

CAG

AD

C: caudate

A: decreased Ach

G: Gaba

95
Q

Myotonic dystrophy

Trinucleotide repeat (________)

Mode of inheritance (______)

Mnemonic ……

A

(CTG)n

AD

C: cataracts

T: toupee (early balding in men)

G: gonadal atrophy

96
Q

Fragile X syndrome

Trinucleotide repeat (________)

Mode of inheritance (______)

Mnemonic ……

A

(CGG)n

XD

Chin protruding, Giant Gonads

97
Q

Friedreich Ataxia

Trinucleotide repeat (________)

Mode of inheritance (______)

Mnemonic ……

A

(GAA)n

AR

Ataxic GAAit

98
Q

Which trisomy is the most common liveborn chromosomal abnormality?

A

Down syndrome

99
Q

Which disorder is the most common genetic intellectual disability?

A

Down syndrome

100
Q

What are the findings for down syndrome, facial features?

A

depressed nasal bridge, low set ears, short neck, brachy cephaly

101
Q

What are the findings for down syndrome, eye features?

A

Prominent epicanthal folds, palpebrel fissures, brush field spots

102
Q

What are the findings for down syndrome, extremities features?

A

Sandle toe, single palmer crease

103
Q

What are the five As of Down syndrome

A 
Atresia
Advanced maternal age
Atrioventricular septal defect 
Alzheimer disease (early onset) (codes for amyloid precursor protein, chromosome 21)
AML/ALL
hirschsprung disease
104
Q

95% of the cases are due to ______________

A

Meiotic non disjunction

105
Q

Which cause of down syndrome increases with advanced maternal age

A

Meiotic non disjunction

106
Q

What is the incidence of Down syndrome in women less near 20 years of age

A

1:1500

107
Q

What is the incidence of Down syndrome in women less near 45 years of age

A

1:25

108
Q

4% of the cases are due to ______________

A

Unbalanced Robertsonian translocation, between 14 and 21 chromosomes

High occurence within families
No relation w maternal age

109
Q

1% of the cases are due to ______________

A

Post fertilization mitotic error

Can lead to milder forms of DS
No association with advanced maternal age

110
Q

What are the invasive methods of diagonising Down syndrome

A

Amniocentesis

Chorionic villus sampling

111
Q

What are the non invasive methods of diagnosing Down syndrome

A

Nuchal translucency, depressed nasal bones growth

112
Q

Which trisomy is Edwards?

A

Trisomy 18

Election 18

113
Q

What is the incidence of Edwards syndrome

A

1:8000

114
Q

What is the second most common cause of autosomal trisomy resulting in live birth

A

Edwards syndrome

115
Q

What are the findings of Edwards Syndrome

A

prince edward sissor hands

Low set ears
Clenched fists

Prominent occiput
Rocker bottom feet
Intellectual disability 
Non disjunction 
Clenched fists
Low set ears
116
Q

What happens to the jaw in patients with edwards syndrome

A

Micrognathia

117
Q

At what age do edwards syndrome patients die

A

Death occurs by 1, congenital heart disease

118
Q

Which trisomy is Patau syndrome

A

Trisomy 13

Puberty 13

119
Q

What are the common findings of Patau syndrome?

A 
Cleft palate 
Prosencephaly 
Polydactyl 
Polycystic kidney disease 
Cutis A Plasia
120
Q

What age do patients of Patau syndrome die?

A

Death occurs by age 1

121
Q

What is the incidence of Patau Syndrome

A

1:15000

122
Q

In the 1st trimester for 21, 18, 13

Beta hcg, and PAPP-A

A

All decreased except b hcg for down syndrome which increases

123
Q

In the 2nd trimester for 21, 18, 13

AFP, b hcg, estriol, inhibin A

A

Normal for 13, decreased for 18, increased for b hcg and inhibin A for 21

124
Q

In the 2nd trimester for 21, 18, 13

AFP:

A

Decreased, decreased, normal

125
Q

Robertsonian translocation is a translocation that commonly involves the chromosome pairs:

A

13, 14, 15, 21, and 22

126
Q

Robertsonian translocation occurs when the _________ fuse at the centromere and the ___________

A

Long arms of 2 acrocentric chromosomes (chromosomes with centromeres near the end)

And the 2 short arms are lost

127
Q

Balanced translocation normally do not cause any ___________

A

Abnormal phenotype

128
Q

Unbalanced translocations can result in __________

A

Miscarriage, still birth, and chromosomal imbalance e.g down syndrome, patau syndrome

129
Q

Cri du chat syndrome is the ____________

A

Deletion on the short arm of chromosome 5

130
Q

What are the findings in patients with cri du chat syndrome?

A

Microcephaly, moderate to severe intellectual disability, high pitched screaming, epicanthal folds, and cardiac abnormalities (VSD)

131
Q

What is the genetic cause in Williams syndrome?

A

Microdeletion on chromosome 7 long arm

132
Q

The deleted region in Williams syndrome includes the _______

A

Elastin gene

133
Q

What are the findings in Williams syndrome

A

Elfin facies
Intellectual disability
Well developed verbal skills
Extreme friendliness with strangers

Hypercalcemia (sensitivity to vitamin D increases)
Cardiovascular problems (supravalvular aortic stenosis, renal artery stenosis)
134
Q

What is the genetic cause in digeorge syndrome?

A

22q11

Microdeletion at chromosome 22 long arm region one band one

135
Q

What are the findings of 22q11 syndrome

A

CATCH 22

cleft palate, Abnormal facies, Thmyic aplasia (t cell def), cardiac defects, hypocalcemia (parathyroid aplasia) due to aberrent development of 3th and 4th pharyngeal pouches

136
Q

What are the findings of digeorge syndrome?

A

Thmyic, parathyroid and cardiac defects

137
Q

What is the findings of Velocardiofacial syndrome?

A

Palate, facial and cardiac defects

biochemistry (11 decks)

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