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Clin Med III - Psych, Genetics > Genetics > Flashcards

Genetics Flashcards

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1
Q

What is the functional unit of the genome? How is it regulated?

A
  • Gene

- Transcription

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2
Q

Define transcriptome

A

Expressions of genes modified by external influences (acetylation, phosphorylation, etc.)

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3
Q

Define microbiome

A

Constellation of viruses, bacteria, and fungi that colonize various human tissues

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4
Q

How much of DNA is expressed?

A
  • Only 10% (25,000 genes)

- Other 90% do not encode genes and may serve a structural role

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5
Q

What causes gene silencing?

A

Methylation of cytosine

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6
Q

What does methylation of cytosine result in?

A

Gene silencing

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7
Q

Define imprinting

A

Inherited methylation of certain genomic regions (e.g. silencing of one X chromosome in females)

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8
Q

How many codons are possible?

A

4 bases (4^3) = 64

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9
Q

Describe codons

A
  • Triplet of bases (64 possible)

- Each codon specifies 1 of 20 different amino acids

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10
Q

Define degeneracy vs. ambiguity

A
  • Multiple codons can specify 1 amino acid (degeneracy)

- BUT a codon will only encode 1 protein

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11
Q

What is the initiation codon?

A

AUG

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12
Q

What are the termination codons?

A

UAA
UAG
UGA

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13
Q

Among women in their 40s, more than 25% of all pregnancies are estimated to involve:

A
  • Trisomic conception

- Vast majority of these spontaneously abort (only trisomy 13, 18, 21, and sex chromosome survive to term)

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14
Q

Describe trisomy 13

A
  • Median survival 2.5 days (1 in 20 survive more than 6 months)
  • Holoprosencephaly (forebrain fails to develop into hemispheres)
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15
Q

How do infants with trisomy 18 present?

A

Clenched fist with 2nd and 5th digits overlapping the 3rd and 4th

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16
Q

Describe Klinefelter Syndrome

A

47, XXY karyotype

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17
Q

How do males with Klinefelter present?

A
  • Thin build, disproportionately long arms and legs
  • Mostly normal intelligence
  • Gynecomastia
  • Testicular dysgenesis
  • Taurodontism (enlargement of molar teeth)
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18
Q

What is Klinefelter with subnormal intelligence or mental retardation associated with?

A

Higher number of X chromosomes

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19
Q

What are the Klinefelter variants?

A
  • 48, XXYY
  • 48, XXXY
  • 49, XXXYY
  • 49, XXXXY
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20
Q

Describe XYY super male

A
  • Nondisjunction at 2nd meiotic division (fertilization with 2 sperms would result in 69, XYY)
  • Learning problems at school
  • Delayed emotional maturity
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21
Q

Describe Turner Syndrome

A
  • XO
  • Short stature
  • Ovarian failure w/high LH/FSH
  • Webbed neck 2/2 lymphedema
  • Ortho abnormalities
  • Shield chest
  • HTN
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22
Q

Webbed neck and shield neck indicates:

A

Turner Syndrome (XO)

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23
Q

Gynecomastia and testicular dysgenesis with normal intelligence indicates:

A

Klinefelter Syndrome

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24
Q

Describe XXX syndrome

A

Typically no unusual physical features/medical problems

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25
Q

Why are there usually no physical features/medical problems a/w XXX syndrome?

A

Inactivation of all but 1 X chromosome

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26
Q

Define silent mutation

A

No ultimate consequence

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27
Q

Define missense mutation

A
  • Change occurs in a coding region and alters an amino acid

- May result in non-functional protein

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28
Q

Define nonsense mutation

A
  • Reading frame alteration results in an abnormal protein segment
  • Usually results in unstable or non-functional protein
29
Q

Define penetrance

A

% of individuals having a particular genotype that EXPRESS the expected phenotype

30
Q

Define full penetrance

A

The gene mutation for a disease always results in the phenotypic change (if you have the gene, you WILL develop the disease)

31
Q

Define incomplete penetrance

A

Individuals with abnormal genotype who do NOT have the disease

32
Q

What is a disease that exhibits age dependent penetrance?

A

Huntington’s (delay in the age of onset of expression - symptoms not usually seen until 30 or older)

33
Q

Define penetrance vs. expression

A
  • Penetrance = PERCENTAGE of people with particular genotype that show expected phenotype
  • Expression = DEGREE to which a phenotypic characteristic is exhibited
34
Q

What has a higher mutation rate - oogenesis or spermatogenesis?

A

Spermatogenesis
-30 cell divisions by puberty, 20 each year after
(whereas oogenesis only 20 cell divisions to complete)

35
Q

Spermatogenesis and deleterious mutations?

A

Approx 1 in 10 sperm carries a new deleterious mutation

36
Q

What is the Hardy-Weinberg equation?

A

For 2 alleles (A and a), frequency of the genotypes: p^2 + 2pq + q^2 = 1

37
Q

What does p^2, 2pq, and q^2 refer to for Hardy-Weinberg equation?

A 
p^2 = frequency of AA
2pq = frequency of Aa
q^2 = frequency of aa
38
Q

Define overdominance

A

Occurs when heterozygote has a higher fitness than either homozygote

39
Q

Advantage of sickle cell trait to malaria

A
  • RBCs don’t sickle in trait until reduced oxygen tension
  • Malaria parasite reduces oxygen tension within the RBCs
  • RBCs in these pts then sickle and reduce parasitic burden
40
Q

Define epigenetics

A
  • Study of heritable changes in gene expression or cellular phenotype
  • Caused by mechanisms other than changes in underlying DNA sequence (e.g. DNA methylation or histone deacetylation)
41
Q

Define genomic imprinting

A

Epigenetic process that involves methylation and histone modifications in order to achieve monoallelic gene expression w/o altering genetic sequence

42
Q

What is Prader-Willi syndrome?

A
  • Disruption/deletion short arm paternal chromosome 15

- Maternal chromosome 15 imprinted (SILENCED)

43
Q

What is Angelman syndrome?

A
  • Disruption/deletion short arm maternal chromosome 15

- Paternal chromosome 15 imprinted (silenced)

44
Q

Which syndrome consists of a silenced (imprinted) paternal chromosome 15?

A

Angelman syndrome

45
Q

Which syndrome consists of a silenced (imprinted) maternal chromosome 15?

A

Prader-Willi syndrome

46
Q

What are examples of autosomal dominant conditions?

A

Huntington’s
Achondroplasia
PKD

47
Q

How do X-linked recessive conditions show up in families?

A
  • All are fully evident in males (only 1 X chromosome, no normal gene to compensate)
  • Women are rarely affected (only if 2 copies of mutant allele)
  • NO father to son transmission
  • All daughters of affected male will be affected (since father only has 1 X to transmit)
48
Q

How do Y-linked conditions show up in families?

A
  • Affects only males
  • Affected males ALWAYS have affected fathers
  • All sons of affected male are affected
49
Q

How is mitochondrial DNA inherited?

A

Exclusively through maternal line (only the ovum contributes mitochondria to offspring)

50
Q

How do children with multifactorial inheritance present?

A

Most affected children have normal parents

51
Q

How should an individual with a dominant trait be called?

A

“Obligate heterozygote”

-Should NOT be called carrier (reserved for recessive traits)

52
Q

What is FISH used for?

A

Help detect DNA sequence deletions or excess chromsome material

53
Q

Direct vs. indirect FISH

A
  • Direct: probe contains fluorophore (faster)

- Indirect: extra step w/nonfluorescent hapten on probe

54
Q

What should a mass genetic screening program fulfill?

A
  1. Tested disorder is prevalent and serious
  2. It can be pre-symptomatically impacted through lifestyle changes, meds, etc.
  3. Identification of risk does NOT result in undue discrimination/harm
55
Q

How does hyperphenylalaninemia present?

A
  • Severe mental retardation (IQ 30)
  • Hyperactivity
  • Seizures
  • Light complexion
  • Eczema
56
Q

How to achieve best outcome of PKU?

A

Elimination diet started in 1st month

57
Q

What is the primary basis of carcinogenesis?

A

Genetic alterations of cell regulatory systems

58
Q

Genetic alterations of cell regulatory systems results in:

A

Carcinogenesis

59
Q

Major classes of cancer genes

A
  1. Tumor suppressor genes
  2. Oncogenes
  3. DNA repair genes
60
Q

Describe tumor suppressor genes

A
  • Normally inhibit cellular proliferation

- Recessive properties (both copies must be inactivated)

61
Q

Describe oncogenes

A
  • Normally activate cellular proliferation

- Dominant properties (only one copy needs to be mutated to result in unregulated growth)

62
Q

Describe DNA repair genes

A
  • Involved in DNA repair mechanisms

- Defective genes means breaks are NOT repaired

63
Q

What 3 elements are required for gene transfer?

A
  1. Vector
  2. Transgene (gene to be delivered)
  3. Relevant target cell
64
Q

Define transduction of gene therapy

A

Donated DNA enters target cell, expresses the transgene

65
Q

Define the human genome project

A

Determine complete sequence of the 3 billion DNA subunits (bases)

66
Q

Purposes of mapping human genome

A
  • Enhanced understanding of disease
  • Detection of infectious pathogens
  • Diagnostic testing accuracy
  • Treatment of disease
67
Q

What is GINA?

A
  • Genetic Information Nondiscrimination Act

- Prohibits health insurers and employers from using your genetic info against you (for hiring, firing, promotions)

68
Q

What are the exceptions to GINA?

A
  • Does not apply to employers with less than 15 workers

- Covers health insurance but not life or long term care insurance

69
Q

What is MicroSort?

A
  • Way to determine gender for conception

- More effective for girls than boys

Clin Med III - Psych, Genetics (9 decks)

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