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Foundations > Medical Genetics > Flashcards

Medical Genetics Flashcards

1
Q

Genotype

A

the genetic makeup of a cell

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2
Q

phenotype

A

observable/expressed traits

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3
Q

allele

A

a variant form of a gene that exists at the same relative location on homologous chromosomes

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4
Q

locus

A

location of a gene on a chromosome

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5
Q

homozygous

A

inherits the same set of alleles for a particular gene from both parents

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6
Q

homozygous dominant

A

two copies of the dominant allele

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7
Q

homozygous recessive

A

two copies of the recessive allele

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8
Q

heterozygous

A

different alleles of a particular gene

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9
Q

hemizygous

A

a genetic variant on a gene where there is only a SINGLE copy

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10
Q

Genotype to Phenotype

A

genotype–> protein-chemical/enzymatic phenotype–> clinical-chemical/metabolic phenotype–> clinical phenotype

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11
Q

Genotype to Phenotype PKU example

A

homozygosity for R408W mutation–> Phenylalanine hydroxylase activity low–> elevated phenylalanine in blood–> severe intellectual disability, seizures, spasticity, hypopigmentation (untreated pts)

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12
Q

4 Types of genetic diseases

A

single gene
mitochondrial
chromosomal abnormalities
multifactorial disorders

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13
Q

Types of Single Gene/Monogenic Disorders

A

Autosomal - dominant and recessive

Sex-linked - dominant and recessive

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14
Q

Law of Dominance

A

alleles can be dominant or recessive–> the dominant one will be expressed exclusively

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15
Q

Law of Segregation

A

offspring have an equal likelihood of inheriting either gene

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16
Q

Law of Independent Assortment

A

genes do not influence each other with regard to sorting into gametes; every possible combination of alleles for every gene is equally likely to occur

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17
Q

Recurrence Risk

A

probability of producing a child with the genetic disease

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18
Q

Autosomal Dominant

A

recurrence risk = 50%
generation after generation
the ratio is equal M:F

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19
Q

Autosomal Recessive

A

recurrence risk = 25%
seen in multiple siblings but not in earlier generations
the ratio is equal M:F
consanguinity is sometimes seen

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20
Q

Consanguinity leads to incidence of

A

congenital malformations, AR disorders, hearing loss, and mental retardation

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21
Q

Non-Mendelian Modes of Inheritance

A

incomplete dominance, codominance, multiple alleles, polygenic inheritance, linked genes, pleiotropy, and epistasis

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22
Q

Incomplete Dominance

A

heterozygous phenotype is in-between AA and aa

Eg. familial hypercholesterolemia

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23
Q

Codominance

A

two alleles are simultaneously expressed

Eg. Blood type AB

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24
Q

Multiple alleles

A

3 or more alternative allelic forms of a gene, only two of which can exist
Eg. blood types–> A, B, O

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25
Q

Polygenic Inheritance

A

the combined effect of mutations in multiple genes

Eg. height, weight, skin color, eye color

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26
Q

Linked Genes

A

genes that are physically close to one another on the same chromosome and are likely to be inherited together
Eg. Sex-linked diseases

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27
Q

Pleiotropy

A

genes that exert effects on multiple aspects of physiology or anatomy
Eg. Marfan syndrome, cystic fibrosis

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28
Q

Epistasis

A

effects of one gene are modified by one or several other genes

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29
Q

New Mutations/de novo

A

no family hx; mutation occurs in a dominant allele; common in autosomal dominant inherited diseases
Eg. achrondroplasia- short limbs compared to trunk length

30
Q

Mosaicism

A

the occurrence of two or more genetically different cell lines within a tissue or an organism–> can be somatic or germline

31
Q

Somatic Mosaicism

A

a mutation occurs in somatic cells; clinical significance depends on when the mutation happened during the early development

32
Q

Germline Mosaicism

A

all or part of a parent’s germline is affected by a disease-causing mutation; elevated recurrence risk in offspring
Eg. osteogenesis imperfecta(OI), chondroplasia, neurofibromatosis type 1, Duchenne muscular dystrophy, hemophilia A

33
Q

Incomplete/Reduced Penetrance

A

a person with a disease-causing genotype does not exhibit the disease phenotype; they can transmit the disease-causing allele to the next generation
Eg. retinoblastoma, breast cancer, other cancer

34
Q

Age-dependent Penetrance

A

delay in the age of onset of a genetic disease; mutation is present at birth but symptoms appear later in life
Eg. hemochromatosis(AR disorder of iron shortage), familial Alzheimer disease(neurogenerative), inherited cancers(AD breast cancer), Huntington disease(progressive neurodegenerative, AD-trinucleotide repeat expansion, anticipation)

35
Q

Locus Heterogeneity

A

single disease phenotype can be caused by mutations at different loci in different families
Eg. adult polycystic kidney disease (APKD)=AD, progressive accumulation of renal cysts
OI too

36
Q

Variable Expression

A

disease phenotype with variable degree of severity; genetic factors (modifier genes and allelic heterogeneity-different mutation/same site) and nongenetic factors/environmental
Eg. Neurofibromatosis type 1/NFK1/Recklinghausen disease = AD, highly variable phenotype, somatic mosaicism

37
Q

X-linked Dominant

A

50/50 M:F, affected dad=all daughters; generation after generation, 2x as many females affected
Eg. hypophosphatemic rickets, Rett syndrome

38
Q

X-linked Recessive

A

50/50 M:F; affected M=all daughters carriers; skipped generations, greater prevalence of affected M
Eg. Hemophilia A, Duchenne muscular dystrophy, red-green colorblindness

39
Q

Y-linked Disorders/ Holandric

A

father transmits to all of his sons, role in M sexual differentiation, development of sex characteristics, and spermatogenesis

40
Q

Mitochondrial Inheritance

A

mtDNA is inherited exclusively through the mother; falls under the threshold effect= expression depends on the proportion of the cells’ normal mtDNA to mutated mtDNA

41
Q

Heteroplasmy (Mitochondrial Inheritance)

A

mutated mtDNA variant is found only in a portion of the cell’s mitochondria
Eg. Kaerns-Sayre Syndrome; Leber hereditary optic neuropathy(LHON); mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes(MELAS); myoclonic epilepsy and ragged red fiber disease (MERRF)

42
Q

Genetic Imprinting

A

an epigenetic process that differentially modifies genes or chromosomal segments in the M/F germline– either the maternal or paternal allele is active in somatic cells of offspring– chromosomal microdeletions, uniparental disomy
Eg. Prader-Willi, Angelman

43
Q

Anticipation

A

symptoms become more severe or begin at an earlier age as a disease is passed on
Mechanisms: trinucleotide repeats–> number of repeats increases in each generation
Eg. myotonic dystrophy

44
Q

When does crossing over occur in meiosis?

A

prophase 1

45
Q

Metacentric chromosome

A

short and long arms are pretty equal in size(1, 2, 3)

46
Q

submetacentric chromosome

A

chromatids of the short arm are short (4, 5, X)

47
Q

acrocentric chromosome

A

satellites on the short arm are very small (13, 14, 15)

48
Q

Karyotype Analysis

A

detects abnormalities on chromosomes–> can visualize them; locks cells in metaphase arrest
Eg. idiogram, G-banded metaphase spread

49
Q

Euploid

A

the appropriate number of chromosomes for the species

50
Q

Polyploid

A

incompatible with life

51
Q

Aneuploid

A

error in chromosome number; due to nondisjunction during meiosis 1 and 2
Eg. monosomy, trisomy

52
Q

Trisomy 21

A

Down syndrome

53
Q

XXY

A

Klinefelter syndrome

54
Q

Trisomy 13

A

Patau syndrome

55
Q

Trisomy 18

A

Edwards syndrome

56
Q

Monosomy X

A

Turner syndrome

57
Q

Balanced Structural Abnormalities

A

chromosome complement is complete, no loss/gain of genetic info

58
Q

Unbalanced Structural Abnormalities

A

chromosome complement contains an incorrect amount of genetic material; SERIOUS clinical implications

59
Q

Reciprocal Translocation

A

a break occurs in each of the two chromosomes with the segments being exchanges to form two new derivative chromosomes

60
Q

Robertsonian Translocation

A

type of reciprocal translocation in which the breakpoints are located at/close to the centromeres of two ACROcentric chromosomes (to make one new chromosome)

61
Q

Pericentric Inversion

A

inversion segment involves centromere

62
Q

Paracentric Inversions

A

inversion segment involves only one arm of chromosomes–> carrier would not be able to have a viable child

63
Q

Ring chromosomes

A

both tips of a chromosome can be lost, leaving sticky ends that attach to each other

64
Q

Isochromosomes

A

chromosome divides along an axis perpendicular to its usual axis of division–> one chromosome of 2 short arms and one chromosome of 2 long arms

65
Q

Multifactorial/Complex Disorders

A

no clear inheritance pattern; symptoms are caused by the interplay b/w several genes and exogenous factors (polygenic and environment)
Eg. cleft lip, congenital heart defects, neural tube defects, alcoholism, cancer, heart disease

66
Q

What genetic tests can you perform to detect abnormalities in single gene disorders?

A

PCR, Southern Blotting, Northern Blotting, Restriction Fragment Analysis, High-throughput DNA sequencing, microarray analysis

67
Q

What tests would you do to detect dysfunction/variation at the protein level?

A

Electrophoresis and Western Blotting, ELISA, Enzyme activity assays

68
Q

What tests would you do to test for chromosomal abnormalities? cytogenic analyses

A

High-resolution banding, fluorescence in situ hybridization(FISH), comparative genomic hybridization(CGH)

69
Q

FISH Assay

A

a probe is hybridized to metaphase, prophase, or interphase chromosomes; can test for missing or additional chromosomal material as well as rearrangements

70
Q

CGH Assay (comparative genomic hybridization)

A

differentially labeled DNA from test and control sources is hybridized to probes; allows detection of chromosome duplications and deletions

Foundations (6 decks)

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