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uWorld > Genetics- General Principles > Flashcards

Genetics- General Principles Flashcards

1
Q

Neurological comorbidities of Down Syndrome

A
  • Intellectual disability

- Early onset Alzheimer Disease

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2
Q

Cardiac comorbidities of Down Syndrome

A
  • Complete Atrioventricular Septal Defect
  • VSD
  • ASD
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3
Q

GI comorbidities of Down Syndrome?

A
  • Duodenal Atresia (Double-bubble sign): occurs when a portion of the duodenum doesn’t form, resulting in blockage that stops food or fluid from leaving the baby’s stomach
  • Hirschsprung Disease (Congenital Megacolon): Absences of ganglion cells in a segment of the bowel causing decreased peristalsis which results in loss of ability to move stool through the intestine.
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4
Q

Endocrine comorbidities of Down Syndrome?

A
  • Hypothyroidism (High TSH, Low T4)
  • Type 1 Diabetes Mellitus (Autoimmune reaction that destroys beta-cells in pancreas therefore causing decreased insulin production)
  • Obesity
  • Short Stature
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5
Q

Oncologist comorbidities of Down Syndrome?

A

Acute Leukemia

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6
Q

Orthopedic comorbidities of Down Syndrome?

A

Atlantoaxial instability: Excessive movement at the junction between the atlas (C1) and axis (C2) as a result of bony of ligamentous abnormality

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7
Q

Disease characterized by 45, XO

A

Turner’s Syndrome
(Remember they have Streak ovaries)

-Increased risk of Ovarian germ cell tumors

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8
Q

Disease characterized by 47, XXY

A 
Klinefelter Syndrome
(Tall, gynecomastia, small and firm testes, small penis, sparse pubic hair, abnormal body proportions like long legs and short trunk)

-Increased risk of extragonadal germ cell tumors

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9
Q

Homodimeric calcium-binding protein that is a marker for:

  • Neural crest derivation (melanocytes and Schwann cells)
  • Langerhans cells
  • Dendritic cells
A

S-100

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10
Q

X-linked disorder characterized by easy bruising and excessive bleeding due to a deficiency in coagulation factor VIII

A

Hemophilia A

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11
Q

Location and function of enhancers?

A

Location: May be located upstream, downstream, or within introns of the gene

Function: Increase rate of transcription

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12
Q

Location and function of Silencers?

A

Location: May be located upstream, downstream, or within introns of the gene

Function: Decrease rate of transcription by binding repressor proteins

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13
Q

Location and function of the promoter region?

A

Location: 25 or 75 bases upstream from their associated genes

Function: Initiate transcription

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14
Q

Ribosome synthesis occurs primarily in what cell structure?

A

Nucleolus

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15
Q

Enzyme that repairs single-strand breaks in duplex DNA during DNA replication and repair?

A

DNA ligase

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16
Q

Enzyme that unwinds DNA at the replication fork

A

Helicase

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17
Q

Nuclear transcription factors that directly bind DNA via a leucine zipper motif

A

c-Jun and c-Fos

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18
Q

Percentage of expression in offspring for Autosomal dominant conditions when 1 parent is affected?

A

50%

  • Huntington Disease
  • Marfan Syndrome
  • MEN
  • Neurofibramatoses
  • Achondroplasia (gain-of-function mutation in FGFR3 gene)
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19
Q

Percentage of expression in offspring of Autosomal Recessive conditions when both parents are carriers?

A

25% chance the child will have disease because of getting 2 alleles

75% chance child will have 1 or more allele (be careful cause questions can ask it this way)

  • Cystic Fibrosis
  • Hemochromatosis
  • Sickle Cell Anemia
  • Classical Galactosemia
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20
Q

Mutation resulting in a single base SUBSTITUTION that results in the placement of an incorrect amino acid in a protein sequence?

A

Missense Mutation

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21
Q

Mutation resulting from DELETION/addition of a number of bases not divisible by 3 in the coding region of a gene. This dramatically changes the protein structure and often results in the formation of a stop codon.

A

Frameshift Mutation

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22
Q

Mutation that introduces a premature stop codon in a coding region, resulting in the production of a truncated protein?

A

Non-sense Mutation

23
Q

Mutation resulting from a single base substitution that does not change the amino acid. Has no effect on protein formation or function.

A

Silent Mutation

24
Q

Important Mitochondrial Inherited Diseases?

A
  1. Leber Hereditary Optic Neuropathy: leads to bilateral vision loss
  2. Myoclonic Epilepsy: myoclonic seizures and myopathy associated with exercise. Skeletal muscle biopsy shows irregularly shaped muscle fibers (ragged red fibers)
  3. Mitochondrial encephalomyopathy: Presents with lactic acidosis and stroke-like episodes (MELAS)
25
Q

Cause for variability in clinical presentation in mitochondrial diseases?

A

Heteroplasmy: the presence of different mitochondrial genomes (eg, mutated and wild type) within a single cell.

26
Q

3 possible inheritance patterns of Down Syndrome?

A
  1. Meiotic Nondisjunction (most common, 95%): extra comply of Ch. 21 present in every cell)
  2. Unbalanced Translocation: All or part of additional ch. 21 attached to another chromosome
  3. Mosaicism: Some (not all) cells have an extra copy of ch. 21, nondisjunction even early in embryonic life
27
Q

Promotor region that binds transcription factors and RNA Polymerase II during the initiation of transcription and is located approximately 25 bases upstream from the beginning of the coding region?

A

TATA box

28
Q

Responsible for unwinding of Double Helix?

A

Helicase

29
Q

Responsible for removal of supercoils?

A

Topoisomerase II (DNA Gyrase)

30
Q

Responsible for stabilization of unwound template strands?

A

Single-stranded DNA-binding protein

31
Q

Responsible for synthesis of RNA primer?

A

Primase (RNA polymerase)

32
Q

Responsible for 5’ to 3’ DNA synthesis & 3’ to 5’ exonuclease (“proofreading”) activity?

A

DNA polymerase III

33
Q

Same functions of DNA polymerase III but with the additional function of removing RNA primer (5’ to 3’ exonuclease activity) and replacing it with DNA?

A

DNA polymerase I

34
Q

Responsible for the joining of Okazaki fragments (lagging strand)

A

DNA ligase

35
Q

Xeroderma pigmentosum, a rare autosomal recessive disorder occurs due to what defect?

A

Defective nucleotide excision repair of DNA damaged by UV light.

36
Q

Probability that a sibling would be an identical HLA (human leukocyte antigen) match?

A

25%

37
Q

What is it called when there are multiple phenotypic manifestations (often in different organ systems or tissues) resulting from a single genetic mutation?

A

Pleiotropy

38
Q

5 step sequence of nucleotide excision repair?

A
  1. Glycosylase: Remove defective base
  2. Endonuclease: cleaves 5’ end of the corresponding empty sugar-phosphate
  3. Lyase: cleaves the 3’ end of the corresponding empty sugar-phosphate
  4. DNA polymerase: replaces the missing nucleotide
  5. Ligase: seals the final remaining nick
39
Q

Condensed chromatin composed of heavily methylated DNA in tight association with deacetylated histones (which cause it to have a low level of transcriptional activity)?

A

Heterochromatin

*In contrast, Euchromatin is loosely arranged and exhibits a high level of transcriptional activity with acetylated histones

40
Q

Steps of Post-translational modification (mRNA processing to become mature mRNA)?

Note: Mature mRNA refers to mRNA that has been processed and is ready for nuclear export and translation into protein

A
  1. 5’ capping: A 7-methyl-guanosine cap is added to 5’ end of the mRNA
  2. Poly-A tail: added at the 3’ end
  3. Splicing: Removal of introns by spliceosomes

(This whole process occurs within the nucleus)

41
Q

Nomal splicing code of introns?

A

Splice Donor Site: GU at the 5’ splice site
Splice Acceptor Site: AG at the 3’ splice site

Alterations in these code will affect splicing locations

42
Q

What are the 3 stop codons?

A

UAA

UGA

UAG

43
Q

Xeroderma Pigmentosum (Autosomal Recessive) is characterized by defective nucleotide excision repair often caused by deficiency in?

A

UV-specific endonuclease

Affected children usually have severe photosensitivity, hyperpigmentation in sun-exposed areas, and a greatly increased risk for skin cancer.

44
Q

Nucleosides are composed of DNA wrapped around a core of 8 histone proteins. Which histone is located outside of the histone core and helps package nuclosomes into more compact structures?

A

H1 Histone

45
Q

What is the universal start codon and what does it code for?

A
  • AUG

- Codes for methionine

46
Q

What factor recognizes stop codons (UAA, UAG, UGA) and terminates protein synthesis?

A

Releasing factor

47
Q

How is genomic imprinting caused?

A

It is caused by DNA methylation, an epigenetic process in which genes can be silenced by attaching methyl groups to cytosine residues in the DNA molecule.

48
Q

Phenomenon in which the allele of one gene affects the phenotypic expression of alleles in another gene?

A

Epistasis

49
Q

Phenomenon in which a single gene influences multiple phenotypic traits?

A

Pleiotropy

50
Q

Ribonucleoprotein that is a reverse transcriptase which adds TTAGGG repeats to the 3’ end of chromosomes?

A

Telomerase

Stem cells have long telomeres due to high telomerase activity

51
Q

What genes encode DNA-binding transcription factors that play an important role in the segmental organization of the embryo along the cranio-caudal axis?

A

Homeobox genes (Hox gene)

  • Usually about 180 nucleotides in length
  • These genes typically code for transcription factors
52
Q

Disease presenting with must body odor in toddler, intellectual disability, eczema, gait or posture abnormality?

A

PKU (Autosomal Recessive)

53
Q

What is formed in DNA as a result of UV light exposure?

A

Pyrimidine dimers
-These are recognized by endonuclease complex that initiates the process of repair by nicking the damaged strand o both sides of the pyrimidine dimmer. The damaged segment is then excised, and replacement DNA is synthesized by DNA polymerase.

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