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Genetics > Patterns of Inheritance > Flashcards

Patterns of Inheritance Flashcards

1
Q

Autosomal Dominant

A
  • Vertical Inheritance
  • Male:Female ratio equal
  • Male to male transmission seen
  • Only need one allele (het affected)
  • Recurrence risk = 50% at every pregnancy
  • Homozygous always has worse (lethal in achrondroplasia, FHC and Huntington have more severe symptoms and earlier age of onset)
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2
Q

Autosomal Recessive

A
  • Horizontal Inheritance
  • Male:Female ratio equal
  • Male to male transmission seen
  • Parents often carriers, siblings more commonly affected
  • Recurrence risk = 25% risk of being affected at every pregnancy
  • Exacerbated by Consanguinity
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3
Q

Codominance

A

Both traits expressed from both chromosomes

Ie: Blood groups

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4
Q

Familial Hypercholesterolemia

type of inheritance

A

Autosomal Dominant

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5
Q

Huntington Disease

type of inheritance

A

Autosomal Dominant

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6
Q

Myotonic Dystrophy

type of inheritance

A

Autosomal Dominant

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7
Q

Marfan Syndrome

type of inheritance

A

Autosomal Dominant

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8
Q

Osteogenesis Imperfecta

type of inheritance

A

Autosomal Dominant

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9
Q

Achondroplasia

type of inheritance

A

Autosomal Dominant

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10
Q

Neurofibromatosis type I

type of inheritance

A

Autosomal Dominant

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11
Q

Acute Intermittent Prophyria

type of inheritance

A

Autosomal Dominant

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12
Q

Myotonic Dystrophy

A
  • Mutation in DMPK gene
  • Triplet Repeat Disorders (at 3’ UTR)
  • Pleiotropic (many effects from 1 gene)
  • Symptoms: wasting of muscles, cataracts, heart conduction defects, endocrine changes, myotonia (can’t relax muscles after contraction)
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13
Q

Achondroplasia

A
  • FGFR3 mutation
  • ‘Gain of Function’ mutation
  • Codes for receptor that causes cartilage to differentiation to bone too early
  • Symptoms: severe stunting of growth
  • FGFR3 has ‘mutation hot spots’ = new mutations even with no fam history
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14
Q

Neurofibromatosis (NF1)

A
  • NF-1 mutation, many different places —> Allelic Heterogeneity
  • NF-1 gene has mutation hot spots
  • Codes for neurofibromin protein –> tumor suppressor protein (turns RAS off by converting to GDP form)
  • Symptoms: Cafe-au-lait spots, Neurofibromas (swellings on skin), Lisch nodules in iris
  • Has variable expressivity but high penetrance
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15
Q

Haplo-insufficicency

A
  • Explains Autosomal Dominant
  • Loss-of-function mutation. Reduced proteins levels (50%) not sufficient to carry out normal functions
  • Ie: FHC (not enough LDL receptors), Prophyria (enzyme deficiency, can’t produce heme fast enough)
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16
Q

Dominant Negative Mutations

A
  • Explains Autosomal Dominant
  • Mutant gene product interferes with function of normal product. Assembly of multimeric protein can be affected
  • Ie: Osteogenesis Imperfecta, Marfan Syndrome
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17
Q

Gain-of-Function

A

Increased levels of gene expression or development of new function of gene product

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18
Q

Cystic Fibrosis

type of inheritance

A

Autosomal Recessive

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19
Q

Sickle Cell Anemia

type of inheritance

A

Autosomal Recessive

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20
Q

Phenylketonuria

type of inheritance

A

Autosomal Recessive

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21
Q

Tay-Sachs Disease (Hexosaminidase A deficiency)

type of inheritance

A

Autosomal Recessive

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22
Q

Congenital Deafness

type of inheritance

A

Autosomal Recessive

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23
Q

Hemochromatosis

type of inheritance

A

Autosomal Recessive

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24
Q

Alkaptonuria

type of inheritance

A

Autosomal Recessive

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25
Q

Homocystinuria

type of inheritance

A

Autosomal Recessive

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26
Q

Galactosemia

type of inheritance

A

Autosomal Recessive

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27
Q

alpha1-antitrypsin deficiency

type of inheritance

A

Autosomal Recessive

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28
Q

SCID due to adenosine deaminase (ADA) deficiency

type of inheritance

A

Autosomal Recessive

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29
Q

Most enzyme deficiencies in general

type of inheritance

A

Autosomal Recessive

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30
Q

Loss-of-Function mutations

A
  • Explains both Autosomal Dominant and Recessive diseases
  • Results in reduced activity (hypomorph) or complete loss of gene product (null allele or amorph)
  • In recessive, the protein produced from the normal allele (50%) is sufficient to carry out normal functions. Het does not have phenotype
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31
Q

Hemochromatosis

A
  • HFE gene mutation

- C28Y mutation most common but has allelic heterogeneity with H63D mutation

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32
Q

SCID due to adenosine deaminase (ADA) deficiency

A

Enzyme in the purine degradation pathway. When ADA deficient, buildup of dATP is toxic to B-cell and T-cell development

33
Q

Pseudo-autosomal dominant

A
  • Autosomal recessive but appears to follow dominant inheritance pattern
  • Appears vertical transmission, both parents and children may have disease
  • Explanantions:
    1) High Carrier Frequency: sickle cell anemia in Africa (selective pressure of heterozygote because protects from malaria)

2) Higher incidence of consanguinity: due to geographical, social or religious isolation

34
Q

Factors that increase incidence of autosomal recessive traits in population (4)

A
  • Consanguinity
  • Heterozygote advantage (protection against malaria in SCA)
  • Genetic isolation (geographic, religious, cultural)
  • Assortative mating (like marries like)
35
Q

X-linked Recessive Disorders

A
  • More common in males because only need one copy of mutation (hemizygous)
  • Skipped generations
  • Mother of affected sons: obligate carriers
  • Daughters of affected males: obligate carriers
  • NO male to male transmission
  • When child affected, look for maternal relatives (uncle, grandfather, cousin)
36
Q

Duchenne Muscular Dystrophy

type of inheritance

A

X-Linked Recessive

37
Q

Becker Muscular Dystrophy

type of inheritance

A

X-Linked Recessive

less severe form of Duchenne

38
Q

G6PD Deficiency (Glucose-6-Phosphate Dehydrogenase)

type of inheritance

A

X-Linked Recessive

39
Q

Hemophilia A and B

type of inheritance

A

X-Linked Recessive

40
Q

Lesch-Nylan Syndrome (Hypoxanthine Guanine Phosphoribosyl transferase deficiency/HGPRT)

(type of inheritance)

A

X-Linked Recessive

41
Q

Red-green color blindess

type of inheritance

A

X-Linked Recessive

42
Q

X-linked SCID (defect in SCIDX1 gene)

type of inheritance

A

X-Linked Recessive

43
Q

Hemophilia A

A
  • Deficiency of clotting factor VIII, leads to increased bleeding
  • Allelic heterogeneity, many mutations possible for the factor VIII gene
44
Q

X-linked SCID (defect in SCIDX1 gene)

A
  • Defect in gamma chain receptor for interleukins

- T cells can’t mature, results in deficiency of normal B-cell function

45
Q

Manifesting Heterozygote

A
  • In females, due to skewed X-inactivation/skewed lyonization (large number of active mutant X cells)
  • Ie: hemophilia, Duchenne
46
Q

X-linked Dominant

A
  • No skipped generations
  • More females than males
  • NO male to male transmission
  • Affected male transmits to all daughters
  • Can get variable expressivity in females due to X-inactivation
47
Q

Vitamin D resistant Rickets (hypophosphatemic rickets)

type of inheritance

A

X-linked Dominant

48
Q

Rett Syndrome

type of inheritance

A

X-linked Dominant

lethal in males

49
Q

Incontientia Pigmenti

type of inheritance

A

X-linked Dominant

50
Q

Incontinetia pigmentia

A
  • Rashes and blisters early in life
  • Patches of hyperpigmentation (marble cake appearance) later in life
  • Intellectual and learning disability and retinal detachment (in some patients)
  • Variable expressivity in females due to X-inactivation. Darker pigmentation where normal X is inactivated
51
Q

Y-linked Inheritance

A
  • Only males affected
  • Genes on Y generally for spermatogeneis, so mutations usually cause sterility and not passed on
  • Ie: mutations in SRY genes, H-Y histocompatibility antigen, hair ears
  • Males transmit to all their sons
52
Q

Incomplete Penetrance

A
  • When someone has the disease genotype but may not express the disease phenotype
  • May depend on age = “age dependent penetrance”
  • Ie: Huntington has high penetrance but delayed age of onset
  • For autosomal dominant, if penetrance is 80% and recurrence is 50%, there is a 40% risk for the next offspring
53
Q

Variable Expression

A
  • When individuals inherit same allele, some are severely affected others mildly
  • 3 explanations:
    1) random chance
    2) genetic factors (modifier loci)
    3) environmental exposure

Ie:
Hemochromatosis (ion overload) more severe in men bc women menstruate, lose iron

Xeroderma pigmentosum (AR) more severe for people exposed to environmental UV radiation

54
Q

Pleiotropy

A

One mutation affects multiple organ systems

Ie: Marfan syndrome, Osteogenesis Imperfecta

55
Q

Marfan Syndrome

A
  • Mutation in fibrillin-1 gene
  • Pleitropic disease (one mutation, many organs affected)
  • Symptoms: skeletal abnormalities (long limbs, pectus excavatum), hypermobile joints, ocular abnormalities (myopia lens dislocation), cardiovascular disease (mitral valve prolapse, aortic anuerysm)
56
Q

Osteogensis Imperfecta

A
  • Mutation in collagen gene

- Affects bone, sclera

57
Q

Locus Heterogeneity

A
  • Mutations at different LOCI/GENES that cause same disease phenotype
  • Osteogenesis imperfecta: defect in collagen but genes on different chromosomes
  • Breast cancer: BRCA 1 and BRCA 2
  • Congenital deafness
  • Sensorineural hearing impairment, retinis pigmentosa, Charcot Marie Tooth disease, SCID
58
Q

Allelic Heterogeneity

A
  • Different mutations on the SAME gene
  • Neurofibromatosis, >1000 diff mutations in NF-1
  • Hemochromatosis, diff mutaitons in HFE gene
  • Cystic Fibrosis, many mutations in CFTR gene
59
Q

Compound Heterozygote

A
  • Type of allelic heterogeneity

- Can have two different mutations that lead to disease

60
Q

New Mutations

A
  • Unaffected parent to affected
  • No family history of disease
  • Disease usually highly penetrant and Dominant inheritance
  • Often due to increased age of the father (spermatogonia continually divide, high chance for point mutations to occur)
  • Most frequent hot stops for mutations:
    1) NF1 (Neurofibromatosis)
    2) FGFR3 (Achondroplasia)
    3) Dystrophin (Duchenne)
  • Others: Osteogensis Imperfecta, Marfan syndrome
61
Q

Germline (gonadal) Mosaicism

A
  • Mutation is present in a proprotion of the germline cells

- Often the case when unaffected father with no family history of the disease has more than 1 affected child

62
Q

Delayed Age of Onset

A
  • Individuals inherit mutation causing disease at birth but do not manifest phenotype until later in life
  • ie: Huntington disease (progressive dementia, loss of motor control), Hemochromatosis (iron overload), Familial breast cancer (BRCA1 and BRCA2)
63
Q

Huntington Disease

A
  • Autosomal dominant disorder
  • Triplet repeat disorder (CAG repeats in coding region, glutamine accumulation)
  • Delayed age of onset (approx 40 yrs)
  • Symptoms: progressive dementia, loss of motor control
64
Q

Mitochondrial Inheritance

A
  • Inherited from mother only, only females can transmit the disease
  • All offspring (male and female) of affected mother are affected
  • Typically affect multiple organ systems
65
Q

Heteroplasmy

A
  • Accounts for variable expression in mitochondrial disorders
  • Severity of disease depends on number of mutant mitochondria inherited (unequal distribution of mito during cell division)
66
Q

Leber Hereditary Optic Neuropathy

type of inheritance

A

Mitochondrial

progressive blindness around 20-30yrs

67
Q

MELAS
(Mitochondrial Encephaloathy, Lactic Acidosis, and Stroke like episodes)

(type of inheritance)

A

Mitochondrial

68
Q

MERF
(Myoclonic epilepsy with ragged red muscle fibers)

(type of inheritance)

A

Mitochondrial

69
Q

Digenic Disorders

A
  • Mutations in two genes are additive and necessary to produce disorder
  • ie: Retinis Pigmentosa (progressive visual impairment) is a result of mutation in two independent genetic loci (ROM1 and peripherin)
70
Q

Imprinting

A
  • Some genes active only when transmitted from mother or father
  • Involves methylation of specific loci (epigeneticc change) to silence the gene
  • ie: Problems in imprinting pattern on chromosome 15 can lead to Prader Willi Syndrome or Angelman
  • UBE3A active on maternal chromosome 15 (off on paternal)
  • SNRPN active on paternal chromosome 15
    (off in maternal)
71
Q

Prader Willi Syndrome

A
  • Absence of SNRPN gene (UBE3A active, 2 copies)
  • Caused by:
    1) Microdeletion of PATERNAL chromosome 15
    2) MATERNAL uniparental disomy of chromosome 15 (due to trisomy rescue)
  • Symptoms: children obese (can’t stop eating, need to lock the fridge), mental/developmental delay, underdeveloped genitalia, hypotnia in infancy, failure to thrive
72
Q

Angelman Syndrome

A
  • Absence of UBE3A (SNRPN active, 2 copies)
  • Caused by:
    1) Microdeletion of MATERNAL chromosome 15
    2) PATERNAL uniparental disomy of chromosome 15 (due to trisomy rescue)
  • Symptoms: Happy disposition, laugh inappropriately, severe intellectual disability, seizures, puppet like posture of limbs
73
Q

Triplet Repeat Disorder - Promoter Region

A
  • Reduced expression of the gene

- Ie: Fragile X syndrome

74
Q

Triplet Repeat Disorder - Intro

A
  • Formation of heterochromatin

- Ie: Friedrich ataxia

75
Q

Triplet Repeat Disorder - Coding region of the gene

A
  • Results in polyglutamine expansion in the protein

- Ie: CAG expansion in Huntington

76
Q

Triplet Repeat Disorder - 3’ UTR end of gene

A
  • CTG expansion

- Ie: Myotonic Dystrophy

77
Q

Anticipation

A
  • Individuals in recent generations develop disease earlier and with greater severity
  • Disease symptoms become worse with every generation
  • In triplet repeat disorders: greater number of repeats leads to earlier age of onset and more severe
  • Greater number of repeats, greater chance for it to become unstable
  • Depending on disease, severity might be worse if inheriting from mother or father (sex bias)
78
Q

Fragile X Syndrome

A
  • Triplet repeat (CGG) on X chromosome in promoter region
  • Shows anticipation as repeats expand every generation
  • Females less severely affected
  • Symptoms: Intellectual disability, learning difficulties, prominent ears, elongated face, macro orchidism (enlarged testis)

Genetics (1 decks)

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