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Genetics > Patterns of Inheritance - 4 lectures > Flashcards

Patterns of Inheritance - 4 lectures Flashcards

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1
Q

Multiple forms (alleles) of a gene in population (>1% of population)

A

polymorphism

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2
Q

Probability that the offspring of a couple will express the genetic disease

A

recurrence risk

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3
Q

person who approaches a physician or geneticist for a consultation
– this person may, or may not, be affected

A

consultand

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4
Q

affected individual in the family who gains the attention of the physician due to a genetic condition

A

proband

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5
Q

Mitochondrial (due to a mutation in a gene encoded by mitochondrial DNA) has what type of inheritance

A

non mendelian inheritance

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6
Q

do you have father and son affected in X linked dominant disorders

A

nah

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7
Q

difference between vertical and horizontal inheritance

A

vertical does not skip a generation (autosomal dominant) while horizontal does (autosomal recessive)

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8
Q

Autosomal dominant disorders

A

NO HAM 2

neurofibromatosis type I, osteogenesis imperfects, huntingtons, familial hypercholesterolemia type IIa, achondroplasia, AIP, Marfan, Myotonic dystrophy

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9
Q

Most pleiotropic phenotype of all unstable triplet repeat disorders

A

myotonic dystrophy

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10
Q

define pleiotropic

A

one single gene mutation affecting multiple systems

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11
Q

late onset

A

huntingtons, hemochromatosis, homocystinuria

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12
Q

characteristics of myotonic dystrophy

A

wasting of the muscles, cataracts, heart conduction defects, endocrine changes, and myotonia

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13
Q

myotonic dystrophy is mutation in what gene

A

DMPK gene

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14
Q

Mutations in FGFR3 result in severe stunting of growth

A

achondroplasia

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15
Q

Café-au-lait spots, Neurofibromas: swellings on the skin, lisch nodules in the iris of the eye

A

neurofibromatosis type I

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16
Q

neurofibromin gene codes for

A

tumor suppressor protein

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17
Q

mutation in NF-1 gene that has allelic heterogenity and can exhibit variable expressivity

A

neurofibromatosis type I

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18
Q

what is allelic heterogenity

A

mutation can be found at different location/locus on the same gene

basically different mutations on the same locus cause same disease

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19
Q

what is haplo-insufficiency

A

loss-of-function mutations in which half normal levels of the gene product result in phenotypic effects

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20
Q

which autosomal dominant disorders exhibit haplo insufficiency

A

OAF 1
Osteogenesis imperfecta type I
AIP
familial hypercholesterolemia type IIa

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21
Q

a mutant gene product interferes with the function of the normal gene product

A

dominant negative function

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22
Q

which autosomal dominant disorders exhibit dominant negative function

A

MO
Marfan syndrome
Osteogenesis II, III, IV

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23
Q

which autosomal dominant disorders exhibit gain of function

A

HA
Huntington’s
Achondroplasia

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24
Q

prognosis for those who are homozygous for an autosomal dominant disorder

A

prognosis is worse than heterozygote and is usual lethal and is usually rare

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25
Q

what is it called if inheritance is only seen in one generation of the pedigree

A

horizontal inheritance

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26
Q

2/3 chance of being carrier applies to which mode of inheritance

A

autosomal recessive

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27
Q

what are the autosomal recessive disorders

A

How(2) Can(2) She(2) PET GoAts

Hemachromatosis, Homocystinuria, Cystic Fibrosis, Congenital deafness, Sickle Cell, SCIDS - ADA deficiency, PKU, Enzymes (most), Tay Sachs, Galactosemia, Alkaptonuria

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28
Q

2/3 rule doesn’t apply to these autosomal recessive disorders and why

A

hemochromatosis and alkaptonuria

because of delayed age of onset

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29
Q

phenotype of those with autosomal recessive disorder

A

loss of function mutation: so either reduced activity or complete loss of gene

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30
Q

What is the probability of a 30-year-old being homozygous for the normal form of an autosomal recessive disorder if both parents are carriers

A

33%

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31
Q

what does C282Y mutant allele mean in hemachromatosis

A

substitution of tyrosine with cysteine at amino acid position 282 (missense mutation)

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32
Q

Robin’s brother is identified to be a carrier of the C282Y allele of the HFE gene. What is probability of his children having the same mutant allele?

A

50%

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33
Q

if there are two different mutations on the same gene with two different phenotypic manifestations, is it allelic heterogenity?

A

nah because of TWO DIFFERENT MANIFESTATIONS

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34
Q

what happens when deficiency in ADA

A

build up of dATP –> toxic to B and T cells

AKA SCIDS

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35
Q

2’ deoxyadenosine —> 2 deoxyinosine requires what enzyme

A

ADA = adenosine deaminase

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36
Q

Mr. R’s sister is identified to be a carrier of the mutant allele of the ADA gene. What is probability of her grandchildren having the same mutant allele?

A

25% (50% chance multiplied by 50% chance)

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37
Q

define pseudo autosomal dominance

A

an autosomal disease appearing in two or more generations giving the appearance of a dominant inheritance pattern

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38
Q

Factors that can increase incidence of an autosomal recessive trait in a population making it pseudo dominant

A

consanguinity, genetic isolation, heterozygote advantage (think sickle cell), assortative mating

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39
Q

carrier x affected gives appearance of

A

pseudo dominance inheritance

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40
Q

AB blood type is an example of what type of inheritance

A

codominance

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41
Q

person with type A blood can have what type of genotype

A

AA or AO

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42
Q

why are males considered hemizygous

A

if they have the one mutant X allele, then they have the X linked disease

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43
Q

region of chromosome that match

A

pseudoautosomal region

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44
Q

more common - X linked recessive or X linked dominant

A

X linked recessive

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45
Q

who are obligate carriers of X linked recessive diseases

A

mothers of affected son and daughters of affected males

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46
Q

male to male transmission seen in X linked recessive disorder?

A

nah

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47
Q

Recurrence risk for X-linked recessive disease with normal father and carrier mother

A

50% of daughters are carriers while other 50% are homozygous normal

50% of sons are affected while other 50% are normal

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48
Q

Recurrence risk for X-linked recessive disease with affected father and normal mother

A

all daughters are obligate carriers

all sons are normal

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49
Q

Recurrence risk for X-linked recessive disease with affected father and carrier mother (SHIT IS RARE)

A

50% of daughters are affected while the other 50% are carriers

50% of sons are affected while the other 50% are homozygous normal

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50
Q

name the X linked recessive disorders

A

DoGS Really Like Hotdogs

Dystrophins (Duchenne and Becker)
Glucose 6 Phosphate dehydrogenase deficiency
SCIDS - IL2RG receptor defect
Red green color blindness
Lesch Nyhan
Hemophilia A and B
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51
Q

severe and milder form of dystrophy disorder

A

severe - duchenne (all the protein gone)

mild - beckers (have some protein)

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52
Q

why do you hardly see male to male transmission of duchenne

A

has low reproductive fitness - males die before they reach reproductive age

53
Q

phenotypes of person with Duchenne

A

enlarged calves and wasting of thigh muscles

54
Q

big difference in hemophilia A and B

A

hemophilia A - deficiency of clotting factor VIII

hemophilia B - deficiency of clotting factor IX

55
Q

phenotype of person with hemophilia

A

severe bleeding after minor trauma, subcutaneous hematoma, hemarthrosis

56
Q

what is locus heterogenity

A

present on two different loci/chromosome but present with the same phenotype

57
Q

example of disease with locus heterogenity

A

SCIDS - one is on an autosome and one is on a sex chromosome

58
Q

X linked SCIDS is a defect where

A

on the gamma chain of the receptor for several different interleukins (IL2RG)

also called gammaC cytokine receptors

59
Q

problem with duchenne having a low reproductive fitness

A

very high chance of new mutation of this disease arising

60
Q

what does it mean for a female to be a manifesting heterozygote

A

asymmetric X-inactivation/ skewed X inactivation - so a carrier female of a disease would show symptoms of the disease

some mutant cells are activated in most cells while normal cells are at a lower level

61
Q

non lethal sex linked disease

A

red/green color blindness

62
Q

X linked dominant disorders is more common in males or females

A

females

63
Q

status of all daughters of affected male with X linked dominant disorders

A

they will be affected with the disease because they get the mutant allele X from padre

64
Q

male to male transmission in X dominant?

A

nah

65
Q

Recurrence risk for X-linked dominant disease of Affected Father with normal mother

A

all daughters will be affected

all sons will be normal

66
Q

Recurrence risk for X-linked dominant disease with Normal Father and affected mother

A

50% of sons and daughters will be affected

50% of sons and daughters will be normal

67
Q

what are the X linked dominant disorders

A

Rett Syndrome, Vitamin D resistant rickets (hypophosphatemic rickets), incontinentia pigmenti

68
Q

which X linked dominant disorders are lethal in males

A

rett syndrome and incontinentia pigmenti

69
Q

why do females have less severe form of X linked dominant diseases

A

two copies of X - skewed X chromosome inactivation hence have more copies of normal allele in cell than the mutant allele

or disorder could be due to a germline mutation in the mother (germline mosaic)

70
Q

how does incontinentia pigmenti manifest

A

as rashes or blisters in early life
later as patches of hyperpigmentation aka “marble cake appearance”
mental/retinal retardation

71
Q

area of normal skin indicate what in incontinentia pigmenti

A

area where the normal X allele is present while hyperpigmented area is where the mutant allele is present

72
Q

what are the Y linked mutations

A

SHE

various mutation on the SRY gene, H-Y histocompatibility antigen, hairy ears

73
Q

who gets Y linked disorders and what does it cause

A

males and causes sterility sometimes hence are not passed on

74
Q

if a father is affected with a Y linked disorder, what is the recurrence risk of his offsprings

A

all sons will be affected

all daughters will be normal

75
Q

what does non penetrance in an autosomal dominant disorder mean

A

individual has the disease genotype but not displaying disease phenotype buttttttt can still pass it off to offspring

76
Q

disorder is fully penetrant if?

A

all people displaying disease genotype express disease phenotype/show manifestation of disease

77
Q

reasons for incomplete penetrance

A

delayed age onset - for ex: huntingtons

78
Q

what does 80% penetrance of a disorder mean

A

80% of those with disease will display disease phenotype while the other 20% will not

79
Q

what is recurrence risk based on penetrance of a person with an autosomal dominant disease with 80% penetrance

A

first know that there is 50% recurrence risk of autosomal dominant disease

Of those 50%, 40% (50% of 80%) will display the disease phenotype while the other 10% will not

80
Q

reasons for variable expression

A

random chance, genetic factors (modifier loci), environmental exposure

81
Q

what is the mode of inheritance of hemochromatosis and why is it more severe in males than females

A

autosomal recessive disorder

less severe in females because they menstruate

82
Q

why is there variable expression in individuals with xeroderma pigmentosum

A

it is more severe in those who are more frequently exposed to environmental UV radiation

83
Q

what is the penetrance level in individuals affected with neurofibromatosis

A

there is high penetrance but variable expressivity

84
Q

disorders that display pleiotropy

A

marfan syndrome and osteogenesis imperfecta

85
Q

subluxation of lens, extremely tall, arachnodactyly, pectus excavatum, dilation of aorta are all features of?

A

Marfan

86
Q

disorders that display locus heterogenity

A

osteogenesis imperfecta, sensorineural hearing impairment, retinitis pigmentosa, charcot marie tooth disease (AR, AD, X linked), SCID (AR and X linked), breast cancer

87
Q

individual who inherits an abnormal allele from one parent and a different abnormal allele from the other parent hence being affected with the disease is said to be?

A

a compound heterozygote

88
Q

recurrence risk for a new mutation

A

tends to be low

89
Q

disease said to have hot spots for new mutations

A

osteogenesis imperfecta, Duchenne, Neurofibromatosis, achondroplasia, marfan

90
Q

where do new mutation cells come from

A

gamete cells hence not present in parent’s original genome

91
Q

what is the genetic basis of new mutations

A

spermatogonia continually divide & sperm cells from older fathers may contain replication error mutations (point
mutations)

92
Q

when there is no family history of a disease, what is the difference when one child is affected vs. multiple children?

A

one kid affected - new mutation

multiple kids - germline (gonadal) mosaicism

93
Q

diseases that have delayed age of onset

A

huntingtons, hemachromatosis, breast cancer, homocystinuria

94
Q

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

A

her risk - 50%

her offspring - 25%

95
Q

recurrence risk of an offspring of a female with a mitochondrial inheritance disorder

A

100% because all children of affected mother will have disease because we get our mitochondria maternally

96
Q

mitochondrial disorder with variable expression

A

heteroplasmy

97
Q

severity of mitochondrial disorder is dependent on what

A

number of mitochondria that have the mutant gene

98
Q

how does heteroplasmy occur in mitochondrial disorder

A

due to the unequal distribution of mutant and non mutant mitochondrial DNA

99
Q

Thomas has MELAS. What is the recurrence risk of him passing it off to his offspring?

A

0% - males do not pass on their mitochondrial DNA

unless Thomas was once Tina jk

100
Q

what are the mitochondrial diseases

A

MELAS (mitochondrial encephalopathy lactic acidosis and stroke like episodes)

Leber hereditary optic neuropathy

MERRF (Myoclonic epilepsy with ragged red muscle fibres)

101
Q

how does leber hereditary optic neuropathy manifest

A

as progressive blindness at around age 20-30

102
Q

Disorders with non-Mendelian/ unexpected inheritance patterns

A

• Digenic disorders
– Retinitis pigmentosa

• Imprinting
– Prader Willi syndrome
– Angelman syndrome

• Triplet repeat disorders
– Huntington disease
– Myotonic dystrophy
– Fragile X syndrome (X-linked)

103
Q

retinitis pigmentosa is a mutation in what

A

ROM1 and peripherin

104
Q

what must happen in order for a person to have manifestations of retinitis pigmentosa

A

they must have a mutation both in ROM1 and peripherin - at least one mutant allele in both

105
Q

what does it mean for a disorder to be digenic

A

mutations in two genes are additive and absolutely necessary in order to have the disorder

106
Q

what does an imprinting disorder mean

A

some genes are active only from mother while some are active only from the father (methylation) - if something is messed up then there will be manifestation of the disease

107
Q

what is the mutation in Prader Willi

A

Deletion of Paternal 15q11-13 (absence of SNRPN)

so SNRPN missing but mother’s UBE3A present

108
Q

manifestations of Prader Willi

A

obese, mental and developmental delay, hypotonia in infancy, failure to thrive, underdeveloped genatalia (micro-orchidism)

109
Q

how do you detect Prader Willi

A

using FISH

110
Q

what is uniparental disomy

A

two copies of a gene from one parent instead of one from each parent

111
Q

what does restriction enzyme not cleave?

A

methylated DNA

112
Q

reason for uniparental disomy in Prader Willy

A

meiotic I nondisjunction - homologous chromosomes fail to separate

113
Q

what can be used to detect the cause of Prader Willy

A

polymorphic marker analysis

114
Q

Deletion of maternal 15q11-13 (absence of active UBE3A gene)/ Uniparental disomy of paternal chromosome 15 (two copies of active SNRPN and absence of UBE3A gene)

A

Angelman Syndrome

115
Q

Angelman is also called

A

happy puppet syndrome

116
Q

manifestation of angelman syndrome

A

happy disposition, laugh inappropriately, severe mental retardation, seizures, puppet like posture of limbs

117
Q

4 classes of triple repeat disorders

A

Fragile X, Fredlich ataxia, Huntingtons, Myotonic dystrophy

For Free Home Made Triplets

118
Q

triple repeat at promoter region causing reduced expression

A

Fragile X - CGG

fraGGile

119
Q

triple repeat at intron causing heterochromatin

A

Friedrich ataxia - GAA

Get A-taxi-A

120
Q

triple repeat in coding part of gene causing polyglutamine expansion in protein

A

huntingtons - CAG

hunters in CAGe

121
Q

triple repeat at 3’ end (3 UTR) of gene

A

myotonic dystrophy - CTG

both myotonic and dystrophy have T so CTG

122
Q

triple repeat explains this phenomenon - define the phenomenon

A

anticipation

individuals in more recent generation have higher number of triple repeats and disease more severe

123
Q

In a family with myotonic dystrophy, a child is born with infantile myotonic dystrophy. The mother on examination is observed to have ptosis and mild facial weakness. The grandmother has bilateral cataracts and no demonstrable muscle weakness. The phenomenon in this family is/are

A

anticipation

124
Q

manifestations of fragile X

A

anxiety, tantrum, poor muscle tone, Mental retardation, learning difficulties, prominent ears, elongated face, macro orchidism (enlarged testis)

125
Q

fragile X is more severe when who transmits the disease

A

female

126
Q

gene affected in fragile X

A

FMR1 gene methylated and silenced

127
Q

what test is used to diagnose fragile X and what is seen

A

folate deficient medium - southern blotting - X chromosome show breakage

128
Q

A study of the CFTR mutation in two separate families, revealed a codon deletion in one family and a missense mutation in the second family. This illustrates the concept of

A

allelic heterogenity

129
Q

A study of the CFTR mutation in two separate families, revealed a codon deletion in one family and a missense mutation in the second family. A marriage occurred between members of these two families, and a child was born with CF. Which term describes this patient?

A

compound heterozygote

could also be allelic heterogenity

Genetics (19 decks)

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