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Foundations Of Medicine > 13.3 Genetic Variability and Disease > Flashcards

13.3 Genetic Variability and Disease Flashcards

1
Q

How many genes in the human mitochondrial genome

A

37

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2
Q

Define genetic variation

A

Differences in DNA sequences between individuals in a population

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3
Q

What is a genetic polymorphism?

A

A DNA sequence variation that is common in the population

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4
Q

What is a single nucleotide polymorphism?

A

DNA sequence variation that exists within a population and is caused by the change in a single nucleotide

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5
Q

What is a haplotype?

A

Set of polymorphisms close together on a chromosome that are typically passed from one parent more often than expected by chance

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6
Q

What type of DNA mutations are known as “structural variants”?

A

Variation in a region of DNA that is 1kb and larger in size

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7
Q

What are the two mechanisms by which DNA sequence can be altered?

A
  • Mutation (short region of genome by alteration in a nucleotide sequence)
  • Recombination (restructuring a large part of the genome, such as in crossing over)
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8
Q

What is meant by the type of recombination known as translocation?

A

Lengths of DNA exchanged between non-homologous chromosome (e.g. 1 and 8)

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9
Q

How does the position of a mutation in a DNA codon affect severity?

A

Later in codon, less severe, since the mutation is less likely to alter the amino acid that the entire codon codes for

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10
Q

What is a synonymous mutation?

A

Change in DNA, no change in amino acid

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11
Q

What is a nonsense mutation?

A

Change in DNA sequence that encodes “stop”

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12
Q

What is a non-synonymous mutation?

A

Change in DNA, change in amino acid

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13
Q

Conservative vs non-conservative non-synonymous mutation

A

Cons: similar properties
Non-Cons: different properties

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14
Q

What is a readthrough mutation?

A

Stop codon is replaced with another codon, causing gene to be extended beyond its typical end

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15
Q

What are five types of structural variation of DNA sequence?

A
  • Inversion
  • Copy number variation
  • Deletion
  • Insertion
  • Duplication
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16
Q

What is meant by “epigenome”?

A

All epigenetic modifications within the genome that regulate the activity/expression of genesd (AKA epigenetic marks)

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17
Q

List three main types of epigenetic modification

A
  • Histone modifications
  • DNA methylation
  • RNA regulation
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18
Q

What is a 2x2x2 bundle of eight histones with DNA coiled around it called?

A

Nucleosome

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19
Q

Which amino acids in the n-terminal tails of histones are most commonly modified?

A

Lysine and arginine

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20
Q

How do histone modifications impact gene expression?

A

They change whether a gene is wrapped or unwrapped, making them more or less accessible to transcriptional machinery and hence impacting gene expression

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21
Q

Which nitrogenous base is most commonly methylated?

A

Cysotine

22
Q

Which enzyme is required for DNA methylation?

A

Methyltransferase

23
Q

Which dinucleotide is most commonly methylated?

A

CpG (Cytosine phosphate Guanine)

24
Q

Generally, which of methylation and demethylation turn genes on or off?

A

Methylation: off
Demethylation: on

25
Q

What are CpG islands?

A

Regions of genome that contains large number of CpG dinucleotide repeats

26
Q

Give an example where CpG islands in promoter regions of DNA might be used in gene silencing?

A

X inactivation

27
Q

If a gene promoter region is unmethylated, does that mean the gene will definitely be expressed?

A

No; the gene itself (or one section of it) could be methylated

28
Q

What is ncRNA?

A
  • Non-coding RNA
  • RNA that is not translated into a protein
29
Q

What is the role of regulatory nCRNA?

A

Regulate gene expression at epigenetic, post and pre-translational levels

30
Q

What are the two size classifications of ncRNA?

A

Small: <200nt
Long ncRONA: >200nt

31
Q

In what two ways can ncRNA influence gene expression?

A
  • Recruit proteins to modify histones
  • Influencing translation and stability of mRNA
32
Q

Are epigenetic marks passed down to offspring?

A

No

33
Q

Are epigenetic marks carried across generations of cells within an organism once differentiation occurs?

A

Yes

34
Q

What is epigenetic inheritance?

A

Only one copy of a gene is switched on (i.e. only from one parent), which can lead to a vast range of syndromes

35
Q

What is a fluorophore?

A

Fluorescent compound that can re-emit light upon excitation

36
Q

How can DNA polymerase allow for amplification of specific regions of target DNA?

A

By selecting primers which are complementary to the target sequence

37
Q

Describe PCR

A
  • DNA is heated with primers, taq polymerase and free nucleotides (denaturation)
  • Temperature is decreased to the level of the specific primer being used, enabling primer to anneal to DNA; needs to be high enough that no non-complementary linkage will be tolerated (annealing)
  • Temperature is increased to the right level for polymerase, which synthesises complementary strands using free nucleotides
38
Q

How is PCR used in cervical screening tests?

A
  • Detection of Human Papillomavirus (HPV) DNA
  • Identify strain
  • Test is more than just sensitive detection when used to differentiate between strains
39
Q

Describe chromosome microarray

A

Patient DNA and reference DNA (labelled with different fluorophore colours) are added to a slide. Depending on the resulting colour in different regions, we can infer whether there are any deletions or insertions in patient DNA relative to reference.

40
Q

What are some limits of chromosome microarray?

A
  • Cannot detect single gene mutations
  • Almost all genes have some variation, and so it is not always clear whether changes in copy number are pathogenic or not
41
Q

What are some strengths of chromosomal microarrays?

A
  • Good at detecting anything that changes in copy number (including trisomies and monosomies)
  • Can detect these changes on any size within probe resolution
42
Q

How does FISH work?

A
  • DNA in cells is denatured
  • Incubated with fluorophoric probes to see where they can successfully binds
43
Q

What does FISH stand for?

A

Fluorescent in Situ Hybridisation

44
Q

Does FISH have to occur in prophase?

A

No, it can also occur in metaphase, when chromosomes are condensed

45
Q

What can karyotype analysis detect?

A
  • Monosomies/trisomies
  • Translocations
  • Insertions
  • Deletions
46
Q

What are some limitations of karyotype analysis?

A
  • Low resolution
  • Requires culturing of cells to get at start of mitosis
47
Q

Why might whole genome sequencing be of limited clinical value

A

We don’t have the medical understanding to interpret all of the thousands of changes between two haploid genomes, and so we can’t use the data to its full potential

48
Q

Do all pathogenic DNA changes occur in exons within the exome?

A

No; but most do

49
Q

How does genome sequencing differ from exon sequencing?

A

Before sequencing, the genome is processed to enrich exon content

50
Q

How does Non Invasive Prenatal Testing (NIPT) work?

A

During pregnancy, small amounts of foetal DNA are in a mother’s blood. This can be used to assess changes in copy number between maternal and foetal DNA, enabling us to assess for monosomies, trisomies, and even sex identification

51
Q

Is NIPT considered diagnostic?

A

No

Foundations Of Medicine (98 decks)

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