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Genetics > Quiz 2 Review > Flashcards

Quiz 2 Review Flashcards

1
Q
  1. Regarding the tri nucleotide repeat associated with Huntington’s disease, it is

a. CAG repeat that occurs in the 3/ untranslated region?
b. CAG repeat that occurs in the intron
c. CAG repeat that occurs in the exon
d. CAG repeat that occurs in the 5’ untranslated region
e. CAG repeat that occurs in the promoter

A

c. CAG repeat that occurs in the exon

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2
Q
  1. Which of the following complexes of the respritory chain does not contain a subunit encoded by mitochondrial DNA? Complex 1

a. Complex 2
b. Complex3
c. Complex4
d. Complex 5

A

a. Complex 2

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3
Q
  1. A couple both have achondroplasia. They are the only affected individuals in their respective families. The woman is currently pregnant. What is the chance that the fetus has a lethal form of achondroplasia.

a. 0
b. 25%
c. 50%
d. 75%
e. 100%

A

b. 25%

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4
Q
  1. in your pt with amelogenesia imperfect, a laboratory identified the mutation p. Trp153* What does this indicate?

a. A stop codon was eliminated
b. A stop codon was created
c. An amino acid substitution occurred
d. An alteration was fond at nucleotide 153
e. None of the above

A

b. A stop codon was created

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5
Q
  1. Your pt has the following mutation c200+IG>A what does this mean

a. A deletion has occurred
b. A missense mutation has occurred
c. A nonsense mutation has occurred
d. A splicing mutation has occurred
e. An insertion has occurred

A

d. A splicing mutation has occurred

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6
Q
  1. A woman is a carrier for sickle cell anemia. Her husband is not a carrier and does not have sickle cell anemia. If their child has sickle cell anemia, what is the most likely explanation

a. A maternal meiosis 1 error occurred
b. A maternal meiosis 2 error occurred
c. A paternal meiosis 1 error occurred
d. A paternal meiosis 2 error occurred
e. The lady is a tramp

A

b. A maternal meiosis 2 error occurred

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7
Q
  1. Fragile X syndrome is due to a CGG expansion in the 5’ UTR of the FMR1 gene. Affected individuals have over 200 repeats. When the repeats reach this size or larger, the promoter is modified so that no RNA is produced. What is this modification

a. Phosphorylation
b. Acetylation
c. Glycosylation
d. Methylation
e. Hydroxylation

A

d. Methylation

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8
Q
  1. Which of the following is NOT a usual mechanism of diseases for autosomal dominant disorders?

a. Dominant negative
b. Gain of function
c. Haploinsufficiency
d. Loss of function

A

d. Loss of function

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9
Q
  1. Type 1 osteogenesis imperfect WITHOUT dentinogenesis imperfect is due to what molecular mechanism

a. Loss of function
b. Gain of function
c. Haploinsufficiency
d. Dominant negative
e. None of the above

A

c. Haploinsufficiency

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10
Q
  1. Which term describes a disorder like cystic fibrosis where many different mutations give the same clinical phenotype?
    a. Clinical heterogencity
    b. Genetic heterogencity
    c. Allele heterogencity
    d. Locus heterogencity
A

c. Allele heterogencity

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11
Q

Fragile X ?

A

-CGG repeat in 5’ UTR noncoding

  • X-linked
  • > 200 DOSE load required
  • Methylate promoter
  • USE SOUTHERN BLOT
  • Pre-muation carriers
  • Male ATAXIA
  • Repeats don’t expand if passed on by MALE
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12
Q

Huntington’s Disease

A
  • Autosomal Dominant
  • CAG in exon
  • Polyglutamine disorder(repeat expansion smaller in size & variation)
  • -small repeat so PCR

-40 REPEATS & live long enough= magic number for HD

**Toxic GAIN of FUNCTION

-Characterized by progressive neuronal dysfunction that begins in mid-life, resulting in severe neurodegenration

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13
Q

Friedrich Ataxia?

A
  • Autosomal RECESSIVE
  • Intron

-GAA repeat in intron
(Trinucleotide repeat disorder)

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14
Q

Mytotonic Dystrophy

What kind of repeat?
Clinical findings?
Diagnosis?

A

-Autosomal Dominant

  • CTG repeat
  • 3’ region
  • non coding repeat
  • Clinical finding categorized into 3 phenotypes: 1) mild 2) classical 3) congenital

Diagnosis:
-Adults = muscle weakness (distal leg), hand, neck & face. Sustained muscle contraction and cataracts

-Neonates= Club foot, respiratory insufficiently or failure, generalized weakness, facial muscle weakness, & hypotonia.

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15
Q

Achondroplasia?

-Inheritance?

A

Inheritance:

  • Autosomal Dominant
  • Incomplete dominance
  • Homozygous from LETHAL
  • **PATERNAL Single Locus Mutation
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16
Q

Achondroplasia?

-Mutations?

A

Mutations:
- (90%) have new mutations (de novo on paternal chromosome)

-Majority have glycine to arginine substitution at codon 380 (p.G380R).

-99% have G → A transition (substitution of purine for purine)
1% have a G → C transversion (substitution of pyrimidine for a purine)

  • Mutations can cause an alteration of restriction sites, leading to shorter DNA fragments
  • “gain of function” - new or enhanced function of the gene
17
Q

Achondroplasia?

-Diagnosis?

A

Diagnosis?

  • PCR
  • Digestion w/ Restriction enzyme

Parents BOTH w/ Achondroplasia:

  • 25% of lethal form
  • 50% change of Achondroplasia disease
18
Q

Penetrance?

A

Given that someone has inherited the mutant allele, WHAT is the CHANCE that they will EXPRESS the PHENOTYPE.

-Either on or off (light switch example)

19
Q

Variable Expressivity?

A

Given that a person who has inherited a mutant allele expresses the trait, HOW SEVERELY affected are they. (light dimmer example)

20
Q

Anticipation?

A

INCREASED SEVERITY and/or DECREASED AGE of ONSET in successive generations
reflects INCREASED number of REPEATS as passed from generation to generation

21
Q

Imprinting ?

A

**Differential modification & expression of alleles of a gene DEPENDING on (expression passed from maternal & paternal mutations) SEX of the parent of origin.

**Prader-Willi and Angelman Syndromes are the BEST examples in humans of imprinting
(certain genes are silent on one parental chromosome)

**About 31 human genes reported to show imprinted expression

22
Q

Uniparental Disomy ?

A
  • Inheritance of 2 copies of a gene or chromosome FROM 1 PARENT
  • Implications for RECESSIVE disorders and imprinted disorders

(Ex: CF, Prader-Willi, recessive disorders)

23
Q

Tell me about mitochondrial genetics?

A

*Maternal inheritance

  • High mutation rate
  • Limited proofreading and repair
  • Lack of protective histone proteins

*Heteroplasmy - can have both wild type and mutant mitochondrial DNA

*Threshold Effect
need to reach a minimum number of mutant type proteins present before expression occurs

*Mitotic segregation

24
Q

Mutation Nomenclature

p. Gly17Arg?
p. Gly17*
p. Leu6Hisfs*3
c. 101-2A>T

A

p.Gly17Arg
aa substitution, missense

p.Gly17*
STOP codon, nonsense

p.Leu6Hisfs*3
Frameshift mutation due to insertion or deletion of 1 or 2 nucleotides

c.101-2A>T
Splicing mutation of intron

25
Q

If imprinting exists, what molecular mechanisms lead to a clinical phenotype?

A
  • *Lack of inheritance
  • Uniparental disomy
  • Deletion
  • *Failure to reset imprint of allele
  • inherited form parent of opposite sex
26
Q

Regarding Mechanisms of Disease

  • What is dominant negative?
  • Gain of function?
  • Haploinsufficiency?
  • Loss of function?
A

Dominant
-Dominant negative:
Mutant protein interferes w/ function of wild-type protein

  • Gain of fxn: Proteins does something new
    (ex: achondroplasia)
  • Haploinsufficiency: not enough product produced
    (ex: prader willi)

Recessive
-Loss of function:
loss of an enzyme
(ex: PKU)

27
Q

Autosomal Dominant Diseases?

A
  • Achondroplasia
  • Mytotonic Dystrophy
  • Huntington’s Disease
  • NF
  • AI
  • Hereditary Gingival Fibromatosis
28
Q

Define Locus Heterogeneity

A

Mutations in DIFFERENT genes give SAME phenotype (can be X-linked and/or autosomal)

Example: Osteogenesis imperfecta

29
Q

Define Allelic Heterogeneity

A

SAME phenotype by different mutationsin the same gene

-Example: Mutant alleles of the CFTR gene that cause cystic fibrosis.

30
Q

Define Clinical Heterogeneity

A

DIFFERENT phenotypes results from muations in the SAME gene.

31
Q

Define Genetic Heterogeneity

A

SAME phenotype by different genetic mechanism

32
Q

Uniparental disomy arises from?

A

1) Trisomy rescue: disomic egg + fertilized sperm
Only viable = 21, 18, 13
Long term survival = 21

2) Monosomy rescue:
Only viable: Turner Syndrome 45X
contribution from mom and dad

3) Gamete complementation:
**least common mechanism
requires both parents to have non-disjunction

4) Meiosis II: always from mom

Genetics (4 decks)

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