chromosome abnormalities, mutations and analysis mw % + Flashcards
Name the categories of chromosomal abnormalities?
- Numerical
- Structural
- Mutational
Incidence of chromosomal abnormalities
First trimester miscarriages
Liveborn infants
Origins of chromosome abnormalities:
non-disjunction
Trisomy 21 (Down syndrome)
–Incidence: 1 in 650 to 1 in 700
–Average life expectancy (50-60 years)
–Alzheimer’s disease in later life
- Chromosomal findings
- Trisomy 21: non-dysjunction (95%), usually maternal origin
- Unbalanced Robertsonian translocation (4%)
- Mosaicism (1%)
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%)
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
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
47,XXY (Klinefelter syndrome)
–Incidence: 1 in 1000
–Tall stature, long limbs
–Male but infertile, small testes, about 50% gynaecomastia
–Mild learning difficulties
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
Reciprocal translocation carrier:
outcomes (pic)
Robertsonian translocation (pic)
Robertsonian translocation carrier:
outcomes (pic)
What are the types of mutations?
- Non-coding
- Coding
–Silent
–Missense
–Nonsense
–Frameshift
What is a silent mutation?
- CGA (Arg) to CGC (Arg). Same amino acid
What is a missense mutation?
- CGA (Arg) to GGA (Gly). Different amino acid
What is a nonsense mutation?
- CGA (Arg) to TGA (Stop). amino acid ⇒ stop codon
What is a frameshift mutation?
- Frameshift – deletion / insertion
e. g. CGA (Arg) to CCGA (Pro, then out-of-frame)
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
How do you detect mutations?
- Polymerase chain reaction (PCR)
- Gel electrophoresis
- Restriction fragment length polymorphism (RFLP) analysis
- Amplification refractory mutation system (ARMS)
- DNA sequencing
PCR
•In vitro technique
Essentials
- Sequence information
- Oligonucleotide primers
- DNA
- Nucleotides
- DNA polymerase
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
Gel elc (pro-cons)
Advantages
- Speed
- Ease of use
- Sensitive
- Robust
