Mutations and Genetic Analysis Flashcards
What are the different kinds of chromosomal abnormalities?
Numerical
Structural
Mutational
When does first trimester begin and end?
First day of someone’s last period and lasts until the end of week 12 of an embryo’s life
What percentage of miscarriages during the first trimester are due to chromosomal abnormalities?
50%
What are the kinds of numerical abnormalities?
Trisomy (additional chromosomes)
Monosomy (less chromosomes)
What is trisomy?
Additional chromosomes
What is monosomy?
Less chromosomes
What are examples of trisomy?
Patau syndrome (additional 13)
Edwards syndrome (additional 18)
Downs syndrome (additional 21)
Klinefelter (boys have additional X)
Patau syndrome is an additional what chromosome?
13
Edwards syndrome is an additional what chromosome?
18
Downs syndrome is an additional what chromosome?
21
Klinefelter syndrome is an additional what chromosome?
Boys have an additional X chromosome
What is an example of a monosomy?
Turner’s syndrome (female missing all or part of X chromosome)
What chromosome is missing in turner’s syndrome?
Female missing all or part of X chromosome
What is disomy?
The condition of having a chromosome represented twice in a chromosomal complaint
What is aneuploudy?
The presence of an abnormal amount of chromosomes in a cell
What is nondisjunction?
Failure of chromosomes to seperate properly during cell division
What may the origin of nondysjunction be?
Paternal or maternal, with different kinds of trisomys having different likeliness of each
Most autosomal are maternal and sex monosomy sex linked is paternal and trisomy sex linked is even
What are examples of autosomal chromosomes aneuploidy syndromes?
Down syndrome (trisomy 21)
Patau syndrome (trisomy 13)
Edwards syndrome (trisomy 18)
What are the chances of inheriting trisomy 21 (down syndrome)?
1/650
What causes the chances of inheriting down syndrome to increase?
Increases with maternal age
What are some characteristics of down syndrome?
Facial dysmorphologies (birth defects that affect anatomy)
IQ less than 50
Alzheimer’s disease in later life
What is down syndrome normally due to?
Non-dysjunction of chromosome 21 which is usually maternal (95%)
Translocation (5%)
What is the occurance of trisomy 13 (patau syndrome)?
1/1000
What are some characteristics of patau syndrome?
Multiple dysmorphic features and mental retardnation
Very few survive beyond first year
What is patau syndrome normally caused by?
Nondysjunction of chromosome 13 (90%)
Translocation (10%)
What is the occurance of trisomy 18 (edwards syndrome)?
1/3000
What are some characteristics of edwards syndrome?
Severe developmental problems
Most die in first year
What is edwards syndrome normally caused by?
Nondysjunction (90%)
What are some sex chromosomes aneuploidy syndromes?
Turner’s syndrome (45, X)
Klinefelter syndrome (47, XXY)
What is the occurance of turner’s syndrome?
1/5000
What are some characteristics of Turner’s syndrome?
Females of short stature and infertile
Neck webbing and widely spaced nipples
Intelligence and lifespam normal
What is the occurance of Klinefelter syndrome?
1/1000
What are characteristics of Klinefelter syndrome?
Tall stature, long limbs
Males infertile, small testis
Mild learning difficulties
What can structural abnormalities be?
Balanced or unbalanced
What are examples of chromosomal structural abnormalities?
Translocation
Deletions
Insertions
Inversions
What are the two kinds of chromosomal translocation?
Reciprocal (involving breaks in two chromosomes with formation of two new deriviative chromosomes)
Robertsonian (fusion of two acrocentric chromosomes)
What is reciprocal translocation?
Breaks in two chromosomes with formation of two new derivative chromosomes
What is robertsonian translocation?
Fusion of two acrocentric chromosomes
What are acrocentric chromosomes?
Chromosomes in which the centromere is located quite near one end of the chromosome
What is balanced translocation?
Translocation where no genetic material is lost (reciprical translocation)
What is unbalanced translocation?
When someone inherits too much of one chromosome and not enough of another
What does robertsonian translocation result in the loss of?
The short arms of the two acrocentric chromosomes
Where may genetic mutations occur?
Germline or somatic
What does genetic mutation lead do?
Gene disruption
Disease associated
What do genetic mutations not have?
Phenotypic effect
What are different types of genetic mutations?
Non-coding
Coding
What are the different kinds of coding genetic mutations?
Point (only that codon is affected)
Frameshift (codons from that point are affected)
What do point mutations affect?
Only that codon
What do frameshift mutations affect?
Codons from that point
What are examples of point mutations?
Silent (mutation with no change to coded amino acid)
Missense (single nucleotide change results in different amino acid)
Nonsense (single nucleotide change results in stop codon)
What is a silent mutation?
Mutation with no change to coded amino acid
What is a missense mutation?
Single nucleotide change results in different amino acid
What is a nonsense mutation?
Single nucleotide change results in stop codon
What are examples of frameshift mutations?
Deletion (part of sequence lost)
Insertion (insertion of additional nucleotide)
What is a deletion mutation?
Part of sequence is lost
What is an insertion mutation?
Insertion of additional nucleotides
What are the two types of point mutations in relation to purines and pyrimidines?
Transitions (swapping purine for purine (A and G) or pyrimidine for pyrimidine (C and T))
Transversions (swapping purines to pyrimidines and vice versa)
What are transition mutations?
Swapping a purine for a purine or a pyrimidine for a pyrimidine
What are transversion mutations?
Swapping a purine for a pyrimidine and vice versa
What are the purines?
Adesine and guanine
What are the pyrimidines?
Cytosine and thymine
What does the nomenclature of a mutation describe?
Its location in the genome
How is a mutation named?
Describes number from the translation start site (c.10 is 10 nucleotides further into an exon, and c.10+2 is 2 nucleotides into the intron after the exon)
What is an example of naming a point mutation?
c.586C>T (a substitution of a C nucleotide for a T nucleotide at nucleotide 586 within gene)
What is an example of naming a deletion?
c485_488del (a deletion of four nucleotides within a gene, from position c.485 up to and including nucleotide 488)
What is an example of naming a duplication mutation?
c.482_484dup (a duplication of three nucleotides within a gene, from position c.482 up to and including nucleotide c.484)
What is an example of naming an insertion mutation?
c300insATC (an insertion of three nucleotides within a gene, A, T and C, occuring directly after position c.300)
Mutations can be detected by using what?
Polymerase chain reaction (PCR)
Gel electrophoresis
Restriction fragment length polymorphisms (RFLP) analysis
Amplifications refractory mutation system (ARMS)
DNA sequencing
What do we need for polymerase chain reaction (PCR)?
Sequencing information
Oligonucleotide primers
DNA
Nucleotides
DNA polymerase
What is the process of polymerase chain reaction (PCR)?
1) Denaturing (heated to seperate strands)
2) Annealing (cooled to enable DNA primers to attach)
3) Extending (heated and new strand of DNA made by DNA polymerase)
4) Repeated 20 to 40 times, doubling the amount of DNA each time
What does gel electrophoresis do and how?
Seperates DNA fragments by size
It does this by applying an electric field, and because DNA is negatively charged it moves through the agrose gel mix
What are the advantages of PCR?
Speed
Ease of use
Sensitive
Robust
What can PCR be used for?
DNA cloning
DNA sequencing
In vitro mutagenesis
Gene identification
Gene expression studies
Forensic medicine
Typing genetic markers
Detection of mutations
How does amplification refractory mutation system (ARMS) work?
1) Uses constitutive primer which may be a normal primer or a mutant primer
2) If the DNA is that which is expected the normal primer will cause amplification and the mutant primer will not because the bases will not pair
What are the advantages of ARMS?
Cheap
Labelling not required
What are the disadvantages of ARMS?
Need sequence information
Limited amplification size
Limited amount of product
Infidelity of DNA replication
Electrophoresis required
Primer design critical
What is restriction endonucleases?
Enzymes from bacterial cells that degrade the DNA of invading viruses
Recognise specific DNA sequences, usually 4 to 8 base pairs and always cut DNA at the same site
What are advantages of restriction endonucleases?
Simple
Cheap
Non-radioactive
What are disadvantages of restriction endonucleases?
Requires gel electrophoresis
Not always feasible
What is DNA sequencing?
A chain termination method that uses dideoxynucleotides
What are advantages of DNA sequencing?
Gold standard for mutation detection
Automation and high throughput
Fast (18 billion base paires in 4 days, 6 human genomes)
What are disadvantages of DNA sequencing?
Poor quality sequence read
Expensive equipment
What should you consider when deciding what detection method you should use?
Direct test
Quick and easy
Cheap
Sensitivity
Specificity
