Mutations and Genetic Analysis

Question 1

Incidence of chromosomal abnormalities

Answer 1

First-trimester miscarriages = 50%
Children with mental retardation = 35-40%
Congenital malformations = 5-10%

Question 2

trisomy accounts for

Answer 2

50% first trimester miscarriages

Question 3

main trisomy include

Answer 3

other trisomy
trisomy 16
trisomy 21

Question 4

monosomy accounts for

Answer 4

20% first trimester miscarriages

Question 5

trisomy 21 is

Answer 5

downs syndrome

Question 6

Monosomy 45 X means

Answer 6

only 45 chromosomes, one X being missing (this is Turner syndrome).

Question 7

in liveborn infants most common is the abnormality

Answer 7

trisomy 21

45 X

Question 8

Trisomy 47,XX +13 causes

Answer 8

Patau

Question 9

Trisomy 47,XY +18 causes

Answer 9

Edwards

Question 10

Trisomy 47,XX +21

Answer 10

downs syndrome

Question 11

47,XXY causes

Answer 11

Klinefelter

Question 12

in trisomy 13, 18, 21 and and 47XXY, origin of disjunction is usually from

Answer 12

maternal side

Question 13

in monosomy 45X, origin of disjunction is usually from

Answer 13

paternal side

Question 14

Unbalanced Robertsonian translocation (4%) is linked to

Answer 14

downs syndrome

Question 15

Autosomal aneuploidy syndromes:

downs syndrome

Answer 15

Incidence: 1 in 650 to 1 in 700
Characteristic facial dysmorphologies
IQ less than 50
Average life expectancy (50-60 years)
Alzheimer’s disease in later life

Question 16

Autosomal aneuploidy syndromes:
Trisomy 13 (Patau syndrome)

Answer 16

Incidence: 1 in 5000
Multiple dysmorphic features and mental retardation
About 5% die within first month, very few survive beyond first year

Question 17

Unbalanced Robertsonian translocation (10%) is linked to

Answer 17

Trisomy 13 (Patau syndrome)

Question 18

Autosomal aneuploidy syndromes:
Trisomy 18 (Edwards syndrome)

Answer 18

Incidence: 1 in 3000

Severe developmental problems; most patients die within first year, many within first month

Question 19

Sex chromosomes aneuploidy syndromes:

45,X (Turner syndrome)

Answer 19

Incidence: 1 in 5000 to 1 in 10000 (liveborn)
Females of short stature and infertile
Neck webbing and widely spaced nipples
Intelligence and lifespan is normal

Question 20

Sex chromosomes aneuploidy syndromes:

47,XXY (Klinefelter syndrome)

Answer 20

Incidence: 1 in 1000
Tall stature, long limbs
Male but infertile, small testes, about 50% gynaecomastia
Mild learning difficulties

Question 21

Structural abnormalities

Answer 21

Balanced or unbalanced rearrangements
Translocations
Deletions
Insertions
Inversions

Question 22

Reciprocal Translocations:

Answer 22

involving breaks in two chromosomes with formation of two new derivative chromosomes

Question 23

Robertsonian Translocations:

Answer 23

fusion of two acrocentric (near end of one) chromosomes

no genetic information is lost: other translocations occur but do not lead to a viable fetus.

Question 24

deletion mutation is when

Answer 24

breaks in a chromosome leads to part of genetic material being deleted.
- unbalanced rearrangement

Question 25

inversion mutation types

Answer 25

pericentric - breaks in chromosome involving centromere gets inverted paracentric - break in chromosome where part of chromosome gets inverted both are balanced rearrangements

Question 26

genetic mutations can be

Answer 26

``` Germline or somatic Gene disruption /disease-associated Polymorphism - No phenotypic effect - Frequency >1% ```

Question 27

Types of mutations

Answer 27

Non-coding | Coding

Question 28

Coding mutations

Answer 28

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

Question 29

mutations detection methods

Answer 29

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

Question 30

What do we need for PCR?

Answer 30

``` Sequence information Oligonucleotide primers DNA Nucleotides DNA polymerase ```

Question 31

in PCR denaturation occurs at

Answer 31

93-95 degrees C

Question 32

in PCR annealing occurs at

Answer 32

50-70 degrees C

Question 33

in PCR extend occurs at

Answer 33

70-75 degrees C

Question 34

Gel electrophoresis

Answer 34

``` Separate DNA fragments by size Apply an electric field - direction of migration is from negative to positive DNA is negatively charged Separate through agarose gel matrix Visualise DNA fragments ```

Question 35

Advantages of Gel electrophoresis

Answer 35

Speed Ease of use Sensitive Robust

Question 36

PCR applications

Answer 36

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

Question 37

ARMS (Amplification Refractory Mutation System) and primers

Answer 37

normal primer causes amplification mutant primer causes no amplification

Question 38

ARMS (Amplification Refractory Mutation System) | Advantages

Answer 38

Cheap Labelling not required Electrophoresis required Primer design critical

Question 39

ARMS (Amplification Refractory Mutation System) | Disadvantages

Answer 39

Need sequence information | Limited amplification size

Question 40

Restriction endonucleases are

Answer 40

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

Question 41

RFLP analysis is

Answer 41

PCR and digest

Question 42

RFLP Advantages

Answer 42

Simple Cheap Non-radioactive

Question 43

RFLP Disadvantages

Answer 43

Requires gel electrophoresis | Not always feasible

Question 44

DNA sequencing: | Sanger

Answer 44

Chain termination method

Question 45

ddNTP has

Answer 45

h groups

Question 46

dNTP has

Answer 46

OH group

Question 47

DNA sequencing: | Advantages

Answer 47

Gold standard for mutation detection Automation and high throughput Next generation sequencing - 18 billion bp in 4 days (about 6 human genomes)

Question 48

DNA sequencing: | Limitations

Answer 48

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

Question 49

Choice of method

Answer 49

``` Direct test Quick and easy Cheap Sensitivity Specificity ```