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principles of disease > mutations and genetic analysis > Flashcards

mutations and genetic analysis Flashcards

1
Q

defne trisomy

A

3rd copy on one of the chromosomes

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2
Q

define monosomy X

A

only one X chromosome

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3
Q

define tetraploidy

A

whole extra set of chromosomes

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4
Q

numerical chromosome abnormalities

A

change in the number of chromosomes

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5
Q

structural chromosome abnormalities

A

large change in the structure of a chromosome

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6
Q

mutational chromosome abnormalities

A

changes to the DNA sequence

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7
Q

origins of chromosome abnormalities - non-disjunction

A

the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

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8
Q

where do non-disjunction abnormalities tend to occur

A

maternal meiosis

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9
Q

origin of non-disjunction

A

In the female meiosis, the cells are in meiosis I for a very long time before they separate and mature into eggs - this can explain why non-disjunction problems are more common in maternal meiosis

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10
Q

define aneuploidy

A

the condition of having an abnormal number of chromosomes in a haploid set.

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11
Q

autosomal aneuploidy syndromes

A 
trisomy 21 (down's syndrome)
trisomy 13 (Patau syndrome)
trisomy 18 (Edward's syndrome)
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12
Q

trisomy 21

A 
Down's syndrome 
Incidence increases with advancing maternal age
• Characteristic facial dysmorphologies
• IQ less than 50
• Average life expectancy (50-60 years)
• Alzheimer’s disease in later life
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13
Q

chromosomal findings in Down’s syndrome

A

○ Trisomy 21: non-disjunction (95%), usually maternal origin
○ Unbalanced Robertsonian translocation (4%)
○ Mosaicism (1%) - some of the cells in the body have trisomy 21 but others are normal, thought to arise due to non-disjunction error during early cell division

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14
Q

Trisomy 13

A

Patau syndrome
• Multiple dysmorphic features and mental retardation
• About 5% die within first month, very few survive beyond first year
• Non-disjunction (90%), maternal origin
• Unbalanced Robertsonian translocation (10%)

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15
Q

trisomy 18

A

Edwards syndrome
• Severe developmental problems (but is more variable); most patients die within first year, many within first month
Non-disjunction (90%), maternal origin

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16
Q

sex chromosomes aneuploidy syndromes

A

45, X - turner syndrome

47, XXY- Klinefelter syndrome

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17
Q

45, X

A

Turner syndrome
• Incidence at conception much greater, about 97% result in spontaneous loss
• Females of short stature and infertile
○ No Y chromosome therefore cannot be male
• Neck webbing and widely spaced nipples
Intelligence and lifespan is normal

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18
Q

47, XXY

A

Klinefelter syndrome
• Tall stature, long limbs
• Male but infertile, small testes, about 50% gynaecomastia
Mild learning difficulties

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19
Q

types of structural abnormalities

A
  • Balanced or unbalanced rearrangements
  • Translocations (Reciprocal/Robertsonian)
  • Deletions
  • Insertions
  • Inversions
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20
Q

balanced translocation

A

Non-homologous chromosomes

correct sequences of DNA are present in the correct copy number throughout the entire genome

Reattached in the wrong place but the right amount of DNA is still present in the genome

Generally have little negative effect unless by chance an essential gene was hit during the relocation (very rare)

21
Q

reciprocal translocation carrier outcomes

A

formation of two new derivative chromosomes (exchange of the material between 2 chromosomes)

Much more likely to give problems in the next generation where it has occurred in the germ line

Unbalanced genome - missing part of one of the chromosomes but has an extra copy of part of the other chromosome
Depending on the precise nature of this it can give rise to serious defects in the zygote

22
Q

unbalanced translocation

A

Balanced translocation can give rise to unbalanced translocation in the next generation

23
Q

robertsonian translocation

A

fusion of two acrocentric chromosomes

Translocation can lead to loss of short arms and one large chromosome forms containing all of the coding information from the q arms

24
Q

acrocentric chromosome

A

centromere close to one end of the chromosome, p arm is very short (little useful DNA)

25
Q

robertsonian translocation carrier outcomes

A

Where gametes inherit the Robertsonian chromosome and one of the normal chromosomes –> large trisomy/ monosomy

Trisomy 14, monosomy 14 and monosomy 21 aren’t compatible with full term pregnancy

Trisomy 21 - duplication of all the info from chromosome 21, this is the causative aetiology of Down’s syndrome

26
Q

deletions

A

shorter chromosome arises as genetic material is removed

27
Q

inversions

A

balanced rearrangement

piece of DNA is turned around

28
Q

pericentric inversion

A

involving the centromere

29
Q

genetic mutations

A 
• Germline or somatic
• Gene disruption /disease-associated (cancer)
• Polymorphism
	○ No phenotypic effect
Frequency >1%
30
Q

types of genetic mutations

A 
• Non-coding
• Coding
	○ Silent  
	○ Missense 
	○ Nonsense 
	○ Frameshift
31
Q

silent mutations

A

– synonymous e.g. CGA (Arg) to CGC (Arg) - no change in the phenotype

32
Q

missense mutations

A

e.g. CGA (Arg) to GGA (Gly) - depending on the biochemistry this may/may not have a serious effect

33
Q

nonsense mutations

A

e.g. CGA (Arg) to TGA (Stop) - shortens the protein, will probably get degraded

34
Q

frameshift mutations

A

deletion / insertion e.g. CGA (Arg) to CCGA (Pro, then out-of-frame) - changes the reading frame of the rest of the sequence

35
Q

mutation nomenclature: Cys64Arg
1294del40 - 1294
1298A>G

A

cysteine at position 64 changed to arginine

-1294 position, deletion of 40 nucleotides at this position

at position 1298 in the nucleotide sequence, A changed to G

36
Q

detecting mutations

A

• Polymerase chain reaction (PCR)
• Gel electrophoresis
• Restriction fragment length polymorphism (RFLP) analysis
• Amplification refractory mutation system (ARMS)
DNA sequencing

37
Q

PCR

A

amplification of a small amount of DNA

38
Q

what is needed for PCR

A 
• Sequence information
• Oligonucleotide primer
• DNA
• Nucleotides
DNA polymerase
39
Q

gel electrophoresis

A
  • Separate DNA fragments by size
  • Apply an electric field
  • DNA is negatively charged
  • Separate through agarose gel matrix
  • Visualise DNA fragments
40
Q

advantages of gel electrophoresis

A

• Speed
• Ease of use
• Sensitive
Robust

41
Q

PCR applications

A

DNA cloning, DNA sequencing, In vitro mutagenesis, Gene identification, Gene expression studies, Forensic medicine, Typing genetic markers, Detection of mutations

42
Q

ARMS

A

Amplification refractory mutation system

simple method for detecting any mutation involving single base changes or small deletions

43
Q

pros/cons of ARMS

A 
• Cheap
• Labelling not required
• Electrophoresis required
• Primer design critical
Need sequence information
Limited amplification size
44
Q

restriction endonuclease

A 
• Enzymes from bacterial cells
• Protective mechanism
• Degrade DNA of invading viruses
• Recognise specific DNA sequences
• Usually 4-8 bp
Always cut DNA at the same site
45
Q

RFLP analysis

A

involves cutting a particular region of DNA with known variability, with restriction enzymes, then separating the DNA fragments by agarose gel electrophoresis and determining the number of fragments and relative sizes.

46
Q

restriction digest assay

A

procedure used in molecular biology to prepare DNA for analysis or other processing
uses restriction endonucleases to cleave DNA at particular sequences

47
Q

advantages/disadvantages of RFLP

A 
• Simple 
• Cheap
• Non-radioactive
• Requires gel electrophoresis
Not always feasible
48
Q

DNA sequencing

A

• Chain termination method (Sanger)

Use of dideoxynucleotides

49
Q

pros/cons of DNA sequencing

A 
• Gold standard for mutation detection
• Automation and high throughput
• Expensive equipment
• Poor quality sequence read
	○ First part of sequence (15 to 40 bases)
	○ Deterioration after 700-900 bases
• Next generation sequencing
18 billion bp in 4 days (about 6 human genomes)

principles of disease (40 decks)

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