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Principles of Disease-Megan > Chromosome Abnormalities, Mutations and Analysis > Flashcards

Chromosome Abnormalities, Mutations and Analysis Flashcards

1
Q

What type of chromosome abnormalities can occur

A

Numerical
Structural
Mutational

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2
Q

What percentage of first trimester miscarriages are due to chromosomal abnormalities

A

50%

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3
Q

What is the main type of chromosomal abnormalities causing first trimester miscarriages

A

Trisomy

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4
Q

What type of abnormality and syndrome does 47, XX+21

A

Downs syndrome

Means there are 47 chromosomes with the extra chromosome 21

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5
Q

How can chromosomal abnormalities arise

A

From non-disjunction which can occur in meiosis 1 or 2

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6
Q

Give examples of autosomal aneuploidy syndromes

A 
Trisomy 21 (Down syndrome)
Trisomy 13 (Patau syndrome)
Trisomy 18 (Edwards syndome)
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7
Q

Give examples of sex chromosome aneuploidy syndromes

A

45, X (Turner syndrome)

47, XXY (Klinefelter syndrome)

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8
Q

What is the incidence of trisomy 21

A

1 in 650 to 1 in 700 (increases with advancing maternal age)

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9
Q

Describe the features of trisomy 21

A

Characteristic facial dysmorphologies
IQ less than 50
Average life expectancy (50-60 years)
Alzheimer’s disease in later life

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10
Q

What is the incidence of trisomy 13

A

1 in 5000

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11
Q

Describe the features of trisomy 13 (Patau syndrome)

A

Multiple dysmorphic features and mental retardation

About 5% die within first month, very few survive beyond first year

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12
Q

What is the incidence of trisomy 18

A

1 in 3000

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13
Q

Describe the features of trisomy 18 (Edwards syndrome)

A

Severe developmental problems

Most patients die within first year, many within first month

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14
Q

Describe the features of 45, X (Turner syndrome)

A

Females of short stature and infertile
Neck webbing and widely spaced nipples
Intelligence and lifespan is normal

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15
Q

Describe the features of 47, XXY (Klinefelter syndrome)

A

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

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16
Q

What is gynaecomastia

A

Abnormal development of breast tissue in male

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17
Q

What type of structural abnormalites can occur in chromosomes

A 
Balanced or unbalanced rearrangements
Translocations
Deletions
Insertions
Inversions
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18
Q

What type of translocations can occur

A

Reciprocal

Robertsonian

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19
Q

What is a reciprocal translocation

A

Involves breaks in two chromosomes with the formation of two new derivative chromosomes

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20
Q

What is a robertsonian translocation

A

The fusion of two acrocentric chromosomes (the short arms are lost)
The two chromosomes are fused but no genetic information is lost: other translocations occur but do not lead to a viable fetus

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21
Q

What are the outcomes for reciprocal translocation carriers

A

Partial trisomy and partial monosomy

Partial monosomy and partial trisomy

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22
Q

How can an unbalanced translocation occur

A

From the combination of a normal set of chromosomes which a set of balanced translocation chromosomes

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23
Q

What can the robertsonian translocation carriers produce

A

Trisomy 14
Monosomy 14
Monosomy 21
Trisomy 21

24
Q

What occurs in chromosomal deletions

A

A break in the chromosome causes genetic material to be deleted

25
Q

What occurs in a paracentric inversion

A

A break in the chromosome causes DNA to be inverted (switched upside down)

26
Q

What type of inversions are there

A

Paracentric inversion
Pericentric inversion

These are balanced rearrangements

27
Q

What occurs in a pericentric inversion

A

A break in the chromosome which includes the centromere causes DNA to be inverted with the centromere (switched upside down)

28
Q

What kind of genetic mutations can occur

A

Germline

Somatic - in early development or later

29
Q

What types of genetic mutations can occur

A

Non-coding - typically has no effect

Coding

30
Q

What type of coding mutations are there

A

Silent – synonymous e.g. CGA (Arg) to CGC (Arg)
Missense e.g. CGA (Arg) to GGA (Gly)
Nonsense e.g. CGA (Arg) to TGA (Stop)
Frameshift – deletion / insertion e.g. CGA (Arg) to CCGA (Pro, then out-of-frame)

31
Q

What type of point mutations can occur

A

Transitions

Transversions

32
Q

Give examples of transition mutations

A

Purine to purine A > G

Pyrimidine to pyrimidine C > T

33
Q

Give examples of transversions mutations

A

Purine to pyrimidine A > C

Pyrimidine to purine C > G

34
Q

How are mutations named

A

When labelled above they refer to DNA sequence, below refer to protein sequence

35
Q

How can mutations be detected

A

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

36
Q

What is required for PCR

A 
Sequence information
Oligonucleotide primers
DNA
Nucleotides
DNA polymerase
37
Q

How does PCR occur

A

Double stranded DNA is denatured at 93-95oC
Then annealed at 50-70oC
Then extended at 70-75oC
It is then repeated 20-30 times

38
Q

What does gel electrophoresis do

A

Separate DNA fragments by size for analysis (e.g. the ones from PCR)

39
Q

How does gel electrophoresis work

A

Apply an electric field
DNA is negatively charged
Separate through agarose gel matrix
Visualise DNA fragments

40
Q

What are the advantages of PCR

A

Speed
Ease of use
Sensitive
Robust

41
Q

Where can PCR be applyed

A 
DNA cloning
DNA sequencing
In vitro mutagenesis
Gene identification
Gene expression studies
Forensic medicine
Typing genetic markers
Detection of mutations
42
Q

What are the advantages of ARMS

A

Cheap
Labelling not required
Electrophoresis required
Primer design critical

43
Q

What are the disadvantages of ARMS

A

Need sequence information
Limited amplification size
Limited amounts of product
Infidelity of DNA replication

44
Q

What are restriction endunucleases

A

Enzymes from bacterial cells

45
Q

What do restriction endunucleases do

A 
That have a protective mechanism
They degrade DNA of invading viruses
Recognise specific DNA sequences
Usually 4-8 bp
Always cut DNA at the same site
46
Q

What are the advantages and disadvantages of restriction endunucleases

A 
Advantages:
Simple 
Cheap
Non-radioactive
Requires gel electrophoresis
Disadvantages:
Not always feasible
47
Q

What does DNA sequencing use

A

Chain termination method (Sanger)

Use of dideoxynucleotides

48
Q

What are the advantages of DNA sequencing

A

Gold standard for mutation detection

Automation and high throughput

49
Q

What are the disadvantages of DNA sequencing

A

Expensive equipment

Poor quality sequence read (First part of sequence, 15 to 40 bases, Deterioration after 700-900 bases)

50
Q

What should be considered when determining which genetic mutations detecting method should be used

A 
Direct test
Quick and easy
Cheap
High Sensitivity
High Specificity
51
Q

Where is non-disjunction abnormalities more likely to occur

A

The maternal gamates

52
Q

Which chromosomes are acrocentric chromosomes

A 
13
14
15
21
22
53
Q

When are genetic mutations identified

A

When they cause gene disruption or are associated with disease

54
Q

What does PCR do

A

Amplifies DNA

55
Q

What is a new type of sequencing becoming more popular

A

Next generation sequencing - 18 billion bp in 4 days (about 6 human genomes)

Principles of Disease-Megan (41 decks)

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