chromosome abnormalities, mutations and analysis mw % + Flashcards Preview

ME2308 Principles of Disease > chromosome abnormalities, mutations and analysis mw % + > Flashcards

Flashcards in chromosome abnormalities, mutations and analysis mw % + Deck (27)
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1

Name the categories of chromosomal abnormalities?

•Numerical

•Structural

•Mutational

2

Incidence of chromosomal abnormalities

3

First trimester miscarriages

4

Liveborn infants

5

Origins of chromosome abnormalities:
  non-disjunction

6

Trisomy 21 (Down syndrome)

–Incidence: 1 in 650 to 1 in 700

–Average life expectancy (50-60 years)

–Alzheimer’s disease in later life

1. Chromosomal findings

•Trisomy 21: non-dysjunction (95%), usually maternal origin

•Unbalanced Robertsonian translocation (4%)

•Mosaicism (1%)

7

 Trisomy 13 (Patau syndrome)

–Incidence: 1 in 5000

–Multiple dysmorphic features and mental retardation

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

–Non-dysjunction (90%), maternal origin

–Unbalanced Robertsonian translocation (10%)

8

Trisomy 18 (Edwards syndrome) 

–Incidence: 1 in 3000

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

–Non-disjunction (90%), maternal origin

9

 45,X (Turner syndrome)   

–Incidence: 1 in 5000 to 1 in 10000 (liveborn)

–Incidence at conception much greater, about 97% result in spontaneous loss

–Females of short stature and infertile

–Neck webbing and widely spaced nipples

–Intelligence and lifespan is normal

10

                   47,XXY (Klinefelter syndrome) 

–Incidence: 1 in 1000

–Tall stature, long limbs

–Male but infertile, small testes, about 50% gynaecomastia

–Mild learning difficulties

11

 Describe structural abnormalities?

•Balanced or unbalanced rearrangements

Translocations

–Reciprocal: involving breaks in 2 chromosomes with formation of 2 new derivative chromosomes

–Robertsonian: fusion of 2 acrocentric chromosomes 

Note: Acrocentric chromosome: A chromosome in which the centromere is located quite near one end of the chromosome.

•Deletions

•Insertions

Inversions

12

Reciprocal translocation carrier:
  outcomes (pic)

13

Robertsonian translocation (pic)

14

Robertsonian translocation carrier:
  outcomes (pic)

15

What are the types of mutations?

•Non-coding

•Coding

–Silent 

–Missense 

–Nonsense 

–Frameshift 

16

What is a silent mutation?

  • CGA (Arg) to CGC (Arg). Same amino acid

17

What is a missense mutation?

  • CGA (Arg) to GGA (Gly). Different amino acid

18

What is a nonsense mutation?

  • CGA (Arg) to TGA (Stop). amino acid ⇒ stop codon

19

What is a frameshift mutation?

  • Frameshift – deletion / insertion

e.g. CGA (Arg) to CCGA (Pro, then out-of-frame)

20

Mutation nomenclature?

  • Green = exons, black line = introns
  • Cys64Arg ⇒ Cys replaced with Arg at 64
  • M252X ⇒ M is replaced with a stop codon
  • 1294del40 ⇒ 40 are deleted from 1294
  • 662-42C>T ⇒ At 662 - 42, C is replaces  T
  • IVS2 + 12INSG ⇒ At Intervening Sequence 2, + 12, a G is added (intron)
  • 1298A>G ⇒ A replaces G at 1298

21

How do you detect mutations?

•Polymerase chain reaction (PCR)

•Gel electrophoresis

•Restriction fragment length polymorphism (RFLP) analysis

•Amplification refractory mutation system (ARMS)

•DNA sequencing

22

PCR

•In vitro technique

Essentials

•Sequence information

•Oligonucleotide primers

•DNA

•Nucleotides

•DNA polymerase

 

23

Gel electrophoresis 

Technique

•Separate DNA fragments by size

•Apply an electric field

•DNA is negatively charged, so moves towards postive end

•Separate through agarose gel matrix

•Visualise DNA fragments

Applications

•DNA cloning &  sequencing

•In vitro mutagenesis

•Gene identification

•Gene expression studies

•Forensic medicine

•Typing genetic markers

•Detection of mutations

 

24

Gel elc (pro-cons)

Advantages

•Speed

•Ease of use

•Sensitive

•Robust

 

25

  ARMS (Amplification Refractory Mutation System)

ARMS is an application of PCR in which DNA is amplified by allele specific primers.

Advantages

•Cheap

•Labelling not required

Disadvantages

•Electrophoresis required

•Primer design critical

26

Restriction endonuclease

Enzymes from bacterial cells

•Degrade DNA of invading viruses

•Recognise specific DNA sequences

•Usually 4-8 bp

•Always cut DNA at the same site

27

  DNA sequencing

Chain termination method (Sanger)

•Use of dideoxynucleotides

Advantages

Gold standard for mutation detection

•Automation and high throughput

Disadvantages

Expensive equipment

Poor quality sequence read

–First part of sequence (15 to 40 bases)

–Deterioration after 700-900 bases