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Semester 1 - MCBG > 14. Mutation > Flashcards

14. Mutation Flashcards

1
Q

What is mutation?

A

a change of the nucleotide sequence which results in a heritable alteration in a gene or chromosome

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2
Q

What is mutagenesis?

A

the process of mutation generation

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3
Q

Give an example of a spontaneous mutation

A

Spontaneous deamination - cytosine to uracil

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4
Q

What are the 3 types of sources that result in defective or error-prone DNA repair and ultimately mutations?

A

Exogenous sources
Spontaneous events
Endogenous sources

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5
Q

What does endogenous mean?

A

Endogenous substances and processes are those that originate from within a system such as an organism, tissue, or cell

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6
Q

Give 2 types of endogenous sources that result in a mutation

A
  1. DNA replication defects

2. Transposable elements

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8
Q

Is the gene activated or inactivated when a transposable element leaves?

A

Activated

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9
Q

Is the gene activated or inactivated when the transposable element moves in?

A

Inactivated

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10
Q

What is affected when transposable elements go into regulatory regions such as promoter regions?

A

They change WHEN a gene is activated

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11
Q

How does the length of a gene effect the affect of transposable elements?

A

The longer the gene, the more likely that it will be activated or inactivated by transposable elements

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12
Q

Are mutations good or bad?

A
  • may or may not cause a phenotypic change
  • may be ‘good’ or ‘bad’
  • a source of genome variation
  • a driving force of evolution
  • may cause disease
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13
Q

What are single nucleotide polymorphisms(SNP)

A

A single-nucleotide polymorphism (SNP, pronounced snip) is a DNA sequence variation occurring when a single nucleotide in the genome differs between members of a species or paired chromosomes in an individual.

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14
Q

What is anonymous SNP?

A

When the SNP has no known efffect

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15
Q

What is non-coding SNP?

A

When the SNP is outside a gene

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16
Q

What is coding SNP?

A

When the SNP is inside a gene

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17
Q

What are the 6 types of mutations?

A
  1. Substitution
  2. Deletion
  3. Insertion
  4. Duplication
  5. Inversion
  6. Translocation
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18
Q

In transcription, what direction is DNA read in and what direction is mRNA synthesis?

A

DNA is read 3’ to 5’

mRNA synthesis 5’ to 3’

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19
Q

In translation, what direction is mRNA read in and what direction is polypeptide synthesis?

A

mRNA is read 5’ to 3’ polypeptide synthesis N to C

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20
Q

In single nucleotide changes, what is transition?

A

Change to same type of base:

purine to purine (A G ) pyrimidine to pyrimidine (T C)

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21
Q

In single nucleotide changes, what is transversion?

A

Change to different type of base.

purine to pyrimidine or vice versa (A/G C/T)

22
Q

What are the possible effects of single nucleotide changes?

A
  • change gene product (polypeptide or RNA)
  • change the amount of gene product
  • change the polypeptide length
  • do not have an effect
23
Q

What causes sickle cell anaemia?

A

> Mutation in codon 7 of HBB
Base substitution mutation (missense)
One amino Acid change (the 6th amino acid because the first one is MET)
Glutamate —> Valine

26
Q

What are transposable elements and how do they cause mutations?

A
  • specific DNA sequences (>1 gene)
  • supernumerary (many copies)
  • always contained within other DNA molecule
  • move (transpose) as a discrete unit
  • move (transpose) to random sites
  • ubiquitous - all species have them
  • may insertionally inactivate genes or change gene expresssion
27
Q

What are missense mutations?

A

When a base substitution results in a change in the amino acid the gene codes for

28
Q

What are nonsense mutations?

A

When t=a base substitution results in the gene coding for a stop codon

29
Q

What mutations can change the polypeptide length?

A

frameshift
mutation OR mutation of stop codon OR
nonsense mutation

30
Q

What are synonymous mutations?

A

mutations that have no effect because the same amino acid is coded for- silent mutations

31
Q

What are the 3 mutations that base substitution cause?

A

synonymous OR missense OR nonsense mutation

32
Q

What type of mutation do insertion and deletion of nucleotide bases result in?

A

Frameshift

33
Q

What mutations can change the gene product?

A

missense mutation /

non-synonymous mutation

34
Q

What mutations do not have an effect?

A

silent or neutral

mutation / synonymous mutation

35
Q

What mutations can change the amount of gene product?

A

mutations affecting regulatory sequences:

alter promoter activity
alter translation initiation at AUG prevent mRNA splicing
reduce mRNA stability

36
Q

What mutations occur at the micro level?

A

Deletion
Insertion
Substitution

37
Q

What mutations occurs at the macro level?

A
  • Deletions (including microdeletions)
  • Duplications
  • Inversions (paracentric and pericentric)
  • Substitutions / Insertions
  • Translocations (reciprocal & Robertsonian)
  • Isochromosomes
  • Ring chromosomes
  • Marker chromosomes
38
Q

What is Robertsonian translocation?

A
  • when Two different chromosomes where p arm is very small and q arm is very long break at the centromere.
  • The two q arms fuse at the centromere to form a large chromosome
  • The two p arms are lost
  • This means that the individual has 45 chromosomes instead of 46
  • There is no phenotypic effect as the p arms are lost and the q arms act as a single chromosome
39
Q

What is polyploidy?

A

Gain of extra haploid set of chromosomes (3n=69)

40
Q

What is the most common cause of polyploidy?

A

polyspermy- two sperm fuse with one egg

41
Q

What is aneuploidy?

A

loss or gain of whole chromosomes

42
Q

What is the cause of aneuploidy?

A

caused by non-disjunction in meiosis

43
Q

Give 4 examples of trisomies

A

Down syndrome 47,+21; Patau 47,+13;
Edwards 47,+18
Klinefelter syndrome 47,XXY

44
Q

Why are individuals with Klinefelter syndrome phenotypically normally male?

A

They have XXY but one X is always inactivated

45
Q

Give an example of a monosomy that is viable

A

Turner syndrome 45,X

46
Q

What is mosaicism

A

presence of two or more cell lines in an
individual (throughout the body or tissue-
specific)

47
Q

What causes mosaicism?

A

caused by non-disjunction in mitosis

48
Q

How do we test for chromosomal abnormalities?

A

Cytogenetic testing:
• Cytogenetic analysis (karyotyping e.g. 46,XY,inv(7)(p11.2q11.23) = male with chr 7 inversion
• Fluorescent in situ hybridisation (FISH)
• Microarray hybridisation
• DNA sequencing (and other molecular techniques)

49
Q

Why would we do cytogenetic testing?

A

• Accurate diagnosis and prognosis of clinical
problems
(e.g. identify a syndrome, account for a phenotype, account for pregnancy loss)
• Better clinical management (e.g. hormone treatment for Klinefelter syndrome)
• Assess future reproductive risks
(e.g. previous Down’s pregnancy, risk of live born abnormal child)
• Prenatal diagnosis

50
Q

What are the referral reasons for cytogenetic testing?

A
  • prenatal diagnosis
  • birth defects
  • abnormal sexual development
  • infertility
  • recurrent fetal loss
  • leukaemias
  • solid tumours
  • prognostic information for specific translocations
51
Q

What does balanced mutation mean?

A
  • Person has chromosomal abnormality but the phenotype is balanced - no genetic information is lost and/or no phenotypic changes are apparent
  • DNA may be lost - eg p arms lost - but no phenotypic change
52
Q

What does unbalanced mutation mean?

A

There is loss of genetic information and there are phenotypic changes apparent

Semester 1 - MCBG (18 decks)

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