Genetic testing techniques- Seminar 2 Flashcards
(31 cards)
Cytogenetic methods- tests
Cytogenetic method- G banding technique
Molecular cytogenetic methods
FISH
Comparative genomic hybridisation (CGH)
Molecular- genetic methods
Array CGH
Sanger sequencing
Next gen sequencing
When to use cytogenic analysis?
- Multiple congenital anomalies
- Intellectual disability w/ or w/o dysmorphic features
- Ambiguous genitalia
- Impaired growth and puberty
- Infertility, miscarriages
Advantages of cytogenetic analysis
- Gives info on all 23 pairs of chromosomes in a single array
- Used for diagnosis of balanced chromosomal rearrangements
Disadvantages of cytogenetic analysis?
- Takes 10-14 days due to cell cultivation
- Can’t detect submicroscopic rearrangements- microdeletions/duplications
- Can’t be used to detect single-gene disorders
Cytogenetic/chromosomal analysis definition
Chromosomal analysis or karyotyping refers to the analysis of metaphase chromosomes
- it detects numerical and structural chromosomal abberations
What are banding techniques in cytogenetics used for?
To produce a UNIQUE visible karyotype by staining condensed chromosomes
G- banding (giemsa)
Metaphase chromosomes are treated with trypsin to partially digest the proteins and then stained with GIEMSA STAIN
- can observe light and dark bands
Giemsa stain
Regions of DNA rich in A & T- DARK COLOUR
Regions of G & C- LIGHT COLOUR
FISH- Fluorescent in Situ Hybridisation
Combines molecular and cytogenetic testing
- is based on the ability of a portion of a ss DNA to anneal with its complementary target sequence on a metaphase chromosome
Result of FISH is based on…
the number of signals detected when scanning the slide with a fluorescence microscope
Advantages of FISH
Short turnaround time
Can detect microdeletions and duplications
Limitations of FISH
Only specific regions can be studied and detected
Applications of FISH
Detects
- abnormalities of chromosomal structure
- marker chromosomes
- mosaicism
CGH- Comparative genome hybridization method
used to analyse the whole genome for the loss or gain of genetic material in a single experiment
Limitations of CGH array
Can’t identify balanced rearrangements- translocations and inversions
-no diagnosis of single gene disorders
Applications of array CGH
detects chromosomal rearrangments
-cancer genetics
CGH
CGH ARRAY
Molecular cytogenetic
molecular genetic- uses DNA microarray/chip
stages of dna analysis
dna
extraction
amplication
analysis
sources of dna
- EDTA
- fresh, frozen tissue sample
- chorionic villus biopsies
- cultured amniocytes
- buccal swabs
PCR - what is it used for
replicating a short specific DNA sequence very quickly
can be used for sequencing, cloning, analysis
PCR stages
denaturation of ds dna,
annealing of oligonucleotide primers,
synthesis of dna by thermastable dna polymerase
PCR CYCLE
heating and cooking repeated 20 -40 times for 2hrs
