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Medfoundations I > Medical Genetics > Flashcards

Medical Genetics Flashcards

1
Q

Incontinentia pegmenti

A

Disorder of skin, hair, teeth, nailes, eyes, CNS
Skin lesions, alopecia, hypodontia
Cognitive delays, ID

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2
Q

Variable expressivity

A

Different phenotypes in different infividuals, even with identical mutations

ex. Marfan syndrome

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3
Q

Penetrance

A

The proportion of individuals who have a known mutation who express symptoms

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4
Q

Principles of Autosomal dominance

A
  • Vertical transmission
  • Affected males = affected females
  • Male -> male transmission observed
  • Unaffected individuals have unaffected children
  • Disorder may be de novo mutation
  • Phenotype can vary b/t affected people in same family
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5
Q

Principles of autosomal recessive inheritance

A
  • Both parents heterozygotes, unaffected
  • Family hx may be neg or siblings may be affected
  • Affected males = affected males
  • Possible consanguinity in family
  • Ethnic predisposition noted
  • Less clinical variability b/t affected patients
  • Complete penetrance
  • Unaffected offspring have 2/3 chance of being carriers
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6
Q

Principles of X-linked recessive inheritance

A
  • Inicidence much higher in males
  • No male to male transmission
  • Multiple generations affected
  • Carrier females may show variable expression
  • All daughters of affected males are carriers
  • ex. Duchenne muscular dystrophy
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7
Q

Lyonization

A

Inactivation of one of the X chromosomes

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8
Q

Principles of X-linked dominant inheritance

A
  • Females much more likely to be affected
  • Condition often lethal in males
  • Daughters of an afffected male are affected
  • Male to male transmission not observed
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9
Q

Homoplasmy

A

All mtDNA is the same

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10
Q

Heteroplasmy

A

Mixture of normal and abnormal mtDNA

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11
Q

Mosaicism

A

Presence of more than one genetically distinct cell line in an individual

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12
Q

Gonadal mosaicism

A
  • Mutation in germ line cells but not somatic cells
  • Detected when 2 or more offspring present with an autosomal dominant disorder in the face of a negative family history
  • Neither parent has the disorder
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13
Q

Angelman syndrome

A

-Severe ID, movement disorder, seizures
-Lack of expression of genes from maternal allele on chromosome 15
OR
Paternal uniparental disomy of chromosome 15

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14
Q

Prader-Willi syndrome

A

-Hypotonia, ID, hyperphagia
-Lack of expression of paternal allele
OR
Maternal uniparental disomy chromosome 15

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15
Q

Polygenic trait

A

Combined influence of multiple genes, not influenced by environment

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16
Q

Multifactorial trait

A

Combined influence of genes and environment

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17
Q

Quantitative trait

A

Caused by additive effects of genetic and environmental factors, measured on numerical scale

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18
Q

Threshold traits

A
  • Either absent or present, only present after certain point is reached
  • In mitochondrial inheritance, a certain amount of abnormal mtDNA can be tolerated without symptoms, but symptoms will appear once threshold is surpassed
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19
Q

Recurrence risk rules

A
  • Higher if more than 1 family member affected
  • Greater the severity of disease, the greater the recurrence risk
  • Risk greater if proband is of the less commonly affected sex
  • Risk decreases rapidly in more remotely related individuals
  • Risk for 1st degree relatives is approx the sqrt(pop incidence of the trait)
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20
Q

Heritibility

A
  • Disease more common in biologic relatives
  • Monozyg twins more freq concord
  • Monozyg twins reared separately–more frequenly condordant
  • Monozyg twins reared sep have higher coordinace than chance
  • Adopted children more closely resemble biologic parents
21
Q

Birth defect

A

Condition present at birth

~4% of children

22
Q

Dysmorphic features

A

Variants of physical features that are present in less than 2-3% of population

23
Q

Syndrome

A

Pattern of multiple anomalies thought to be related due to a genetic factor

24
Q

Association

A
  • A nonrandom occurrence in two or more individuals due to an unknown factor
  • VATER - vertebral anomalies, anus (imperforate), trachea/esophageal fistula, renal or radial anomalies
25
Q

Sequence

A

Pattern of multiple anomalies derived from single known or presumed anomaly due to a mechanical factor

26
Q

Malformation

A

Morphologic defect of an organ or part of the body resulting from an intrinsically abnormal developmental process

i.e. cleft lip

27
Q

Deformation

A

Abnomal form or position of a body part caused by non-dirsruptive mechanical forces

i.e. clubfoot, congenital dislocation of the hip

28
Q

Disruption

A

Morphologic defect interering with an originally normal development process

i.e. amniotic band syndrome

29
Q

Dysplasia

A

Abnormal cellular organization within a specific tissue type

i.e. hemangioma, osteogenesis imperfecta

30
Q

Teratogens

A

Substances that lead to birth defects; severity depends on gestational age

  • infections
  • medications
  • drugs of abuse
  • external agents
  • maternal disorders
31
Q

Duchenne muscular dystrophy

A

X-linked recessive disease

Delayed motor milestones, waddling gait, calf hypertrophy

32
Q

MELAS

A

Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes

33
Q

Myotonic dystrophy

A
  • Result of anticipation - epansion of CTG repeats
  • Cataracts, mild hypotonia (sustained muscle contraction)
  • Muscle weakness and wasting, ID
34
Q

Fragile X syndrome

A
  • Result of anticipation – expansion of CGG repeat in FMR1 gene on X chr
  • Most common cause of inherited ID
  • Large facial features, long face, large ears
  • Full mutation - FMR1 fully methylated (unmethylated <200 CGG repeats)
35
Q

Pallister-Killian syndrome

A
  • Caused by mosaic tetrasomy 12p

- Low muscle tone, high arched palate, hypopigmentation, extra nipples, developmental delays, diaphragmatic hernias

36
Q

Incomplete penetrance

A

When individuals fail to express the trait despite carrying the allele

ex. BRCA gene mutations

37
Q

Imprinting

A

Epigenetic modification of materna and paternal genetic contributions - change methylation patterns

38
Q

Uniparental disomy

A

Offspring inherits two copies of one chromosome from a single parent

39
Q

Russell Silver syndrome

A

Uniparental disomy of chromosome 7

Small triangular face with distinctive facial features

Growth disorder with prenatal onset

40
Q

Isodisomy vs. heterodisomy

A

Isodisomy - single chromosome from one parent is duplicated ( meiosis II error)

Heterodisomy - pair of non-identical chromosomes are inherited from a single parent ( meiosis I error)

Can also arise from trisomic rescue - fertilized trisomic ovum drops one chromosome to result in a normal diploidy

41
Q

Quantitative trait vs. threshold traits

A

Quantitative: continuous range of measurement, measured on numerical scale, additive effect of multiple genetic and environmentalfactors, bell-shaped distribution

Threshold: trait is either present or absent, bell shaped distribution of liability, individuals exceeding threshold liability express the trait

42
Q

Mitochondrial inheritance

A

Transmission of mtDNA through the maternal line

Mother with heteroplasmy can have affected and unaffected children

43
Q

Trinucleotide Repeats

A

Sequences of three nucleotides that are transmitted as polymorphism to child

Sequences are stable during mitosis and meiosis, appear during DNA replication

44
Q

Anticipation

A

Increase in severity or earlier onset of a phenotype in successive generations

i.e. Trinucleotide repeat disorders (Huntington’s, Fragile X, etc.)

45
Q

SNP

A

Single nucleotide polymorphism,

Observed in groups –> haplotype

Inherited as Mendelian characteristics, differ in different populations

Useful for gene mapping

46
Q

Founder effect

A

Loss of genetic diversity resulting from foundation of a new population by a small group of people, often leading to rare recessive genetic abnormalities

i.e. Ashkenazi Jews & Tay-Sachs, CF in European population

47
Q

Haploinsufficiency

A

Loss of function mutation that results in half of normal product and is insufficient for normal function

Inherited as autosomal dominant trait, with heterozygous individuals likely having mild disease and homozygous having severe disease

48
Q

Dominant negative

A

Gene product is mutated and also interferes with function of protein produced by normal allele

49
Q

Gain of Function mutation

A

Change in gene such that new protein product is made

i.e. achondroplasia - FGFR3 stuck “on”, prevents chondrocyte proliferation

Medfoundations I (3 decks)

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