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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
Polygenic Inheritance
the combined effect of mutations in multiple genes | Eg. height, weight, skin color, eye color
26
Linked Genes
genes that are physically close to one another on the same chromosome and are likely to be inherited together Eg. Sex-linked diseases
27
Pleiotropy
genes that exert effects on multiple aspects of physiology or anatomy Eg. Marfan syndrome, cystic fibrosis
28
Epistasis
effects of one gene are modified by one or several other genes
29
New Mutations/de novo
no family hx; mutation occurs in a dominant allele; common in autosomal dominant inherited diseases Eg. achrondroplasia- short limbs compared to trunk length
30
Mosaicism
the occurrence of two or more genetically different cell lines within a tissue or an organism--> can be somatic or germline
31
Somatic Mosaicism
a mutation occurs in somatic cells; clinical significance depends on when the mutation happened during the early development
32
Germline Mosaicism
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
Incomplete/Reduced Penetrance
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
Age-dependent Penetrance
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
Locus Heterogeneity
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
Variable Expression
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
X-linked Dominant
50/50 M:F, affected dad=all daughters; generation after generation, 2x as many females affected Eg. hypophosphatemic rickets, Rett syndrome
38
X-linked Recessive
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
Y-linked Disorders/ Holandric
father transmits to all of his sons, role in M sexual differentiation, development of sex characteristics, and spermatogenesis
40
Mitochondrial Inheritance
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
Heteroplasmy (Mitochondrial Inheritance)
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
Genetic Imprinting
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
Anticipation
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
When does crossing over occur in meiosis?
prophase 1
45
Metacentric chromosome
short and long arms are pretty equal in size(1, 2, 3)
46
submetacentric chromosome
chromatids of the short arm are short (4, 5, X)
47
acrocentric chromosome
satellites on the short arm are very small (13, 14, 15)
48
Karyotype Analysis
detects abnormalities on chromosomes--> can visualize them; locks cells in metaphase arrest Eg. idiogram, G-banded metaphase spread
49
Euploid
the appropriate number of chromosomes for the species
50
Polyploid
incompatible with life
51
Aneuploid
error in chromosome number; due to nondisjunction during meiosis 1 and 2 Eg. monosomy, trisomy
52
Trisomy 21
Down syndrome
53
XXY
Klinefelter syndrome
54
Trisomy 13
Patau syndrome
55
Trisomy 18
Edwards syndrome
56
Monosomy X
Turner syndrome
57
Balanced Structural Abnormalities
chromosome complement is complete, no loss/gain of genetic info
58
Unbalanced Structural Abnormalities
chromosome complement contains an incorrect amount of genetic material; SERIOUS clinical implications
59
Reciprocal Translocation
a break occurs in each of the two chromosomes with the segments being exchanges to form two new derivative chromosomes
60
Robertsonian Translocation
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
Pericentric Inversion
inversion segment involves centromere
62
Paracentric Inversions
inversion segment involves only one arm of chromosomes--> carrier would not be able to have a viable child
63
Ring chromosomes
both tips of a chromosome can be lost, leaving sticky ends that attach to each other
64
Isochromosomes
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
Multifactorial/Complex Disorders
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
What genetic tests can you perform to detect abnormalities in single gene disorders?
PCR, Southern Blotting, Northern Blotting, Restriction Fragment Analysis, High-throughput DNA sequencing, microarray analysis
67
What tests would you do to detect dysfunction/variation at the protein level?
Electrophoresis and Western Blotting, ELISA, Enzyme activity assays
68
What tests would you do to test for chromosomal abnormalities? cytogenic analyses
High-resolution banding, fluorescence in situ hybridization(FISH), comparative genomic hybridization(CGH)
69
FISH Assay
a probe is hybridized to metaphase, prophase, or interphase chromosomes; can test for missing or additional chromosomal material as well as rearrangements
70
CGH Assay (comparative genomic hybridization)
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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