Mutations and Genetic Analysis Flashcards
what are the 3 chromosomal abnormalities which can occur in chromosomes?
- numerical;
- number of chromosomes - structural;
- rearrangement of chromosomes giving abnormal karyotype - mutational;
- change in DNA sequence
in which trimester of pregnancy are chromosomal abnormalities particularly high?
First
what chromosomal abnormality is common in first trimester?
trisomies
what is trisomy 21?(three copies of chromosome 21)
Down’s syndrome
what condition is 47, XX +13?
Patau;
- dysmorphic features and mental retardation
- few survive beyond 1st year
what condition is 47, XY +18?
Edwards;
- development problems
- most don’t survive by 1st year
what conditions is 47, XX +21?
Down’s Syndrome ;
- Alzherimer’s risk
- IQ<50
- life expectancy is 50/60 years
- facial dysmorphologies
what conditions is 47, XXY?
Klinefelter;
- tall stature
- long limbs
- ingertile men, small testes
- mild learning difficulties
what conditions is 45, X?
Turner syndrome;
- always female since no y chromosome
- short stature, infertile
- neck webbing and spaced nipples
- intelligence and lifespan are normal
where can non-disjunction happen?
in meiosis 1 and meiosis 2
do majority of abnormalities come from the maternal side?
yes; since sperm production happens all the time whereas eggs are present from birth and have higher risk of mutations
what are the two structural translocation reaarrangements?
- reciprocal; breaks in two chromosomes with formation of two acrocentric chromosomes
- Robertsonian; fusion of two acrocentric chromosomes
What are 4 most common rearrangements?
TIID
- deletions
- Insertions
- inversions
- translocations
what is a balanced translocation?
- damage or breakage event in the cell giving rise to TRANSLOCATION
- all genetic info is still there and nothing is lost
- all info still present but just in a different order
- individual is fine
what would give rise to “unbalanced” mutations?
if there was a “missing part” on a chromosome
what is Robertsonian translocation?
- two chromosomes are FUSED together but no genetic info is lost (two long arms get fused and two short arms get fused)
what does acrocentric mean?
when centromere is off to one side of the chromosome (not central); they undergo Robertsonian translocations
what causes deletions in chromosomes?
environmental factors or reapair factors
what are inversions?
- not usually damaging
- pericentric and paracentric inversions can occur
what is pericentric inversion?
involves part of the chromosome which has the entromere on it
what is paracentric inversion?
does not have centromere involved in the inversion
Can genetic mutations be germline or somatic?
Yes
what is genetic mutations typically associated with?
loss of the gene
what are 2 main types of mutations?
- non-doing (doesn’t code for the protein)
2. coding ( affecting coding for the protein)
what is silent coding?
no effect on protein made
what is missense coding?
could have an impact on the protein function which causes the disease
what is nonsense coding?
has an effect on protein function since termination of protein chain arises
what is frameshift coding?
likely to hit a stop codon since it’s becoming abnormal
what are two types of POINT MUTATIONS?
- transitions
(purine to purine or pyrimidine to pyrimidine) - transversions (purine to pyrimidine or pyrimidine to purine)
what are the 5 main methods for detecting mutations?
1, polymerase chain reaction (PCR)
- Gel electrophoresis
- RFLP (restriction fragment length polymorphism analysis)
- ARMS (amplification refractory mutation system)
- DNA sequencing
PCR and ARMS are almost the same thing
what is PCR?
- amplifying DNA (making lots of copies)
- DNA is first denatured , then annealed at low temp. and then extension happens
- oligonucleotide primers used and DNA polymerase
what is gel electrophoresis?
- separates DNA fragments by size and charge after electric field applied
- separation happens through agarose gel matrix
- DNA fragments travel (-ve)
what are main advantages of gel electrophoresis?
- speed
- easy of use (e.g. DNA cloning/ sequencing)
- sensitive (small numbers can be picked up)
- robust (resilient)
give examples where PCR can be used
- DNA cloning and sequencing
- in vitro mutagenesis
- gene identification and expression studies
- forensic medicine
- typing genetic markers
- detection of mutations
what is ARMS? (amplification refractory mutation syndrome)
Includes constitutive primers to be used with normal primers to create amplification of DNA
what is a wild-type allele ARMS process?
- constitutive primer is complementary to normal primer (amplification)
- mutant primer isn’t complementary to constitutive primer (NO amplification)
what is a mutant allele ARMS process?
- constitutive primer isn’t complementary to normal primer ( NO amplification)
- constitutive primer is complementary to mutant primer (amplification)
what are advantages to ARMS?
- cheap
- labelling not required
- electrophoresis required
- primer design is critical (specific primer needs to be made depending on nature of the mutation)
what are disadvantages to ARMS?
- needs sequence information
- limited amplification size
- limited amounts of product
- infidelity of DNA replication (could give rise to mutation)
what are restriction endonucleases?
- enzymes from bacterial cells
- protective mechanism
- degrade DNA of invading viruses
- recognise specific DNA sequences
- usually 4-8 base pairs
- always cut DNA at the same site
what is RFLP?
looking at how far DNA will travel;
- normal: gives rise to restriction site so molecule will move
- mutant: restriction site isn’t there, so fragment will not cut and not move
- heterozygote: normal copy will cut whereas the mutant copy will remain the same
what condition can RFLP diagnose?
sickle cell anaemia
what are advantages of RFLP?
- cheap
- simple
- non-radioactive (safe)
what are disadvantages of RFLP?
- requires gel electrophoresis
- not always feasible
what is DNA sequencing?
- chain termination method (Sanger)
- uses dideoxynucleotides which terminates chains
- allows us to look at changes in the whole DNA fragment
- primer used to remove parts of DNA chain
what are advantages of DNA sequencing?
- gold standard for mutation detections
- automation and high throughput
- next generation sequencing
- wide range
What are disadvantages of DNA sequencing
- extensive equipment
- poor quality sequence read (deterioration occurs after 700-900 bases)
what are the main points to consider when choosing a method for detecting mutations?
- direct test
- quick and easy
- cheap
- sensitivity
- specificity
