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Repro II > Genetics > Flashcards

Genetics Flashcards

1
Q

Mendelian traits

A

AR inheritance patterns

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2
Q

Differences the phenotype produced with the same genotype

A

Genetic variability

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3
Q

Example of genetic variability

A

Osteogenesis imperfecta

  • type 1 - severity varies amongst relatives with the same mutation
  • type 2 - multiple intrauterine fractures, the location, number and timing of each fracture varies
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4
Q

a mutation which does not produce a mutant phenotype in everyone who inherits the mutant genotype

A

Incomplete/partial penetrance

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5
Q

fraction of individuals with a mutant genotype who manifest the mutant phenotype.

A

Penetrance

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6
Q

If 35/100 homozygotes for a mutation are affected then penetrance is…

A

35%

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7
Q

phenotypes determined by multiple factors, genetic & environmental

A

multifactorial traits

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8
Q

phenotypes determined by multiple genes

A

polygenic traits

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9
Q

different mutations producing similar phenotypes

A

heterogeneity

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10
Q

a single gene controlling multiple traits

A

pleiotropy

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11
Q

2 or more alleles for a gene in a population, each with an allelic frequency(q) > 5%

A

polymorphism

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12
Q

different mutations in the same gene producing similar phenotypes

A

allelic heterogeneity

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13
Q

Examples of allelic heterogeneity

A 
CF (over 1000 CFTR mutations)
osteogenesis imperfecta (different mutations of collagen gene)
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14
Q

mutations in different genes producing similar phenotypes

A

locus heterogeneity

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15
Q

Examples of locus heterogeneity

A

SCIDS, Ehler Danlos, thalassemias, congenital deafness

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16
Q

Examples of pleiotropy

A

CF, PKU, Marfan, Hurler, Achondroplasia, neurofibromatosis

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17
Q

Marfan

A

AD, mutations in fibrillin gene
Symptoms: tall, dolichostenomelia (long, thin extremities), arachnodactyly (long digits), pectus excavatum (sunken breastbone), myopia (dislocated lenses), aortic root dilation (risk for aortic aneurysms)

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18
Q

Neurofibromatosis (NF1 gene)

A

peripheral neurofibromata, hyperpigmented macules, Lisch nodules, axillary freckling, macrocephaly, learning difficulties, optic n gliomas, CNS tumors

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19
Q

Neurofibromas

A

pedunculated dermal nodules

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20
Q

different alleles inducing independent effects on the phenotype

A

codominance

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21
Q

Example of codominance

A

Blood type
IAIA – Blood Type A
IAIB – Blood Type AB
IBIB – Blood Type B

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22
Q

two or more alleles for a gene in a population, each with an allelic frequency (q) > 5%

A

Polymorphism

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23
Q

Example of polymorphism

A

IAi – Blood Type A
IBi – Blood Type B
i i – Blood Type O
O is recessive to A and B

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24
Q

transmission from mothers to all children regardless of sex, never transmitted from fathers to any children

A

maternal inheritance

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25
Q

mixed intracellular populations of mitochondria with mutant and wild type genomes. Because the proportions of mutant and wild type mitochondria can change, symptoms can vary from generation to generation, or even during the lifetime of an individual.

A

heteroplasmy

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26
Q

examples of mitochondrial disorders

A

Leber hereditary optic neuropathy (LHON)

Kearn Sayre Syndrome

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27
Q

LHON

A

Point mutations of genes producing components of the NADH dehydrogenase complex I subunits > breaks ox phos pathway and blocks ATP synthesis
-Optic atrophy leading to blindness, telangiectatic microangiopathy

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28
Q

Kearn-Sayre Syndrome

A

Numerous microdeletions of mitochondrial DNA produce this disease. Different genes are lost with the different microdeletions, including components of oxidative phosphorylation.
-Ophthalmoplegia (paralysis of eye muscles), Ptosis (difficulty opening eye), Pigmentary Retinopathy, Hypoparathyroidism, Cardiac Conduction Abnormalities, Diabetes, Deafness

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29
Q

A mutant phenotype that increases in severity each generation

A

anticipation

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30
Q

trinucleotide repeat expansion

A

The number of trinucleotide repeats near or within several genes, will increase in number from generation to generation. The first generation will be wild type, with a normal number of repeats. There will be a modest expansion in the next generation (permutation), with few if any symptoms. This commits the third generation to a greater expansion that will be symptomatic.

31
Q

Example of anticipation d/t trinucleotide expansion

A

Fragile X, Huntington, myotonic MD, spinobulbar muscular atrophy

32
Q

Fragile X

A

X-linked dominant, partial penetrance

  • expansion of upstream repeats attracts hypermethylation > methylation of adjacent promoter inactivates expression of FMR1 gene
  • symptoms: moderate IQ, hyperactivity, hand flapping, biting, temper tantrums, poor eye contact > after puberty: long face, prominent jaw and forehead, large ears, macro-orchidism
33
Q

a mutant genotype with different phenotypes depending on context (e.g. parental sex)

A

Epigenetics

34
Q

If a patient inherits a microdeletion on chromosome 15 from their mother, the patient will have…

A

Angelman syndrome

35
Q

If a pt inherits a microdeletion on chromosome 15 from their father, the patient will have…

A

Prader-Willi

36
Q

Prader-Willi

A

Obesity d/t compulsive feeding
almond-shaped eyes
hypopigmentation

37
Q

Angelman syndrome

A

Paroxysms of laughter
ataxic movements
puppet-like gait
severe intellectual disability

38
Q

genes inactivated by methylation

A

epigenetic imprinting

39
Q

NML methylation patterns on region 15q21

A

SNORD116 and unidentifed genes methylated in mom and paternal alleles expressed
UBE3A gene methylated in dad and maternal allele expressed

40
Q

Prader Willi methylation

A

Microdeletion in father > no expression of SNORD or other unidentified genes (maternal methylated and paternal deleted)

41
Q

Angelman syndrome methylation

A

Microdeletion in mother > no expression of UBE3A (methylated in father, deleted in mother)

42
Q

triploidy fates

A

MC spontaneous abortion
Partial hydatidiform mole > risk of choriocarcinoma
Uncommonly live > will have neonatal mortality

43
Q

the wrong number of homologs (3 or 1) for one chromosome

A

aneuploidies

44
Q

What does frequency of each aneuploidy depend on?

A

Spontaneous abortion rates

45
Q

Down syndrome

A
  • Trisomy 21 (47, XN, +21)
  • Intellectual disability, epicanthal folds, protruding furrowed tongue, brushfield spots, single palmar crease, congenital heart disease, alzheimer’s
46
Q

MC origin of Down

A

Meitotic nondisjunction

47
Q

critical region for Down

A

band q22

48
Q

Edward syndrome

A
  • Trisomy 18 (47, XN, +18)
  • clenched fists (overlapping fingers 2 over 3 and 4 over 5), severe intellectual disability without psychosocial development, short life expectancy, fawn-like ears, rocker bottom feet, micrognathia, growth restriction
49
Q

Complications of Down in infancy

A

heart disease, leukemia, respiratory

50
Q

Complications of Down in late adulthood

A

declining immune function, premature aging, Alzheimer like demetia

51
Q

Patau

A
  • trisomy 13 (47, XN, +13)

- holoprosencephaly, severe intellectual disability w/o psychosocial development, short life expectancy (few days)

52
Q

Turner syndrome

A
  • X monosomy (45, XO)

- webbed neck, broad, shield-like chest, cubitus valgus, prepubertal ovarian failure, streak gonads

53
Q

Klinefelter syndrome

A
  • 47, XXY

- findings after puberty: hypogonadism, gynecomastia, feminized body habitus

54
Q

Extra sex chromosomes

A

Few, if any symptoms

55
Q

Cri du Chat syndrome

A
  • deletion of region near end of short arm of chromosome 5

- cat-like cry

56
Q

Wolf-Hirshorn syndrome

A
  • deletion on short arm of chromosome 4

- frontal bossing, cleft lip, heart defects, severe intellectual disability

57
Q

Structural Damage to Chromosomes

A

chromosomal aberrations

58
Q

submicroscopic deletions of regions with multiple alleles

A

microdeletions

requires FISH

59
Q

Williams syndrome

A
  • cocktail personality

- musical aptitude

60
Q

DiGeorge syndrome

A

CATCH22 syndrome

  • Cardiac defect
  • abnormal facies (small, upturned nose w/ tubular bulbous tip)
  • thymic aplasia (no thymic shadow)
  • cleft palate
  • hypocalcemia
  • chromosome 22
61
Q

Clinical indications for cytogenetic analysis

A
  1. Patient with symptoms suggestive of a cytogenetic syndrome.
    - Due to variability, no symptoms are pathognomonic
    - Aneuploidies, mosaics and aberrations can all have the same symptoms
  2. Unusual symptoms such as intellectual disability or short stature.
  3. Stillborn infant with multiple malformations.
  4. Couple with 2 or more unexplained pregnancy losses (chance of finding abnormality about 5%).
  5. Patient with cancer.
  6. Parents of a child with an aberration. If they are carriers, subsequent progeny can be affected.
  7. Offspring of a parent with a known aberration.
62
Q

Karyotype preparation

A
  1. purify WBCs by centrifugation
  2. culture cells in vivo
  3. treat with mitogen to induce mitosis, suspend mitotic figures w/ colcemid
  4. incubate in hypotonic KCl to swell cells and untangle chromosomes
  5. fix mitotic chromosomes with acetic acid and methanol, stain
63
Q

dark bands on chromosome arms

A

heterochromatic regions

64
Q

light bands on chromosome arms

A

euchromatic regions

65
Q

Preparation of FISH

A
  • DNA probes - replicating fragments with dNTPs that have fluorescent moieties.
  • The probes are complimentary to a specific sequence of a chromosomes.
  • Tissue culture cells are incubated with probe.
  • The probe hybridizes with chromosomes in the nucleus.
  • For metaphase FISH (not interphase FISH), the cells are incubated with a mitogen to produce condensed, mitotic chromosomes.
  • When a probe binds a complementary site, the fluorochromes cause the site to fluoresce under ultraviolet light.
66
Q

aberrations are produced by….

A

DNA ligase error

67
Q

balanced translocations criteria

A
  • No essential chromosomal material can be lost
  • No breakpoints are within an essential gene
  • No gene is moved away from its promoter or enhancer, or to another regulatory region
68
Q

two fragments are exchanged between two chromosomes

A

reciprocal translocations

69
Q

three copies of one translocated segment, one copy of another

A

duplication-deletion syndromes

70
Q

three copies of a chromosomal segment

A

partial trisomy

71
Q

segment is moved from the end of one chromosome to the end of another

A

terminal translocation

72
Q

balanced translocation where the stalks of two acrocentric chromosomes are excised, then the remaining homologs are ligated together end to end

A

Robertsonian translocation

73
Q

Why are progeny who inherit a Robertsonian translocation trisomies but are still 46?

A

Translocated homologs are tied together, but is still trisomic because there are 3 copies of each gene on the chromosome

Repro II (4 decks)

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