Genetic testing

  • Created by: MazzaW
  • Created on: 29-11-19 14:12


Banding and pairing alike chromosomes. Done in lithium heparin sample (14 days turnaround time)

Can show: aneuploidies, balanced/unbalanced translocations, large deletions/duplications

Good for:

  • Down's (trisomy 21/unbalanced Robertsonian translocation in 2%): 47 **/XY +21
  • Edward's (trisomy 18): 47 **/XY +18
  • Patau's (trisomy 13): 47 **/XY +13
  • Klinefelter's: 47 **Y
  • Turner's: 45 X
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Fluorescent in situ hybridisation

Attaches fluorescent tracers to specific DNA sequences

Can detect: aneuploidies, specific deletions and duplications, specific mutations

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Chromosomal microarray. 

Can detect abnormal numbers of genes (should have 2)

Useful for: aneuploidies, unbalanced translocations, deletions/duplications

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Quantitative fluorescent PCR

Rapid screen for common trisomies and sex chromosomes in neonates.

Done in 1-2mL EDTA sample with 48hr turnaround time. If abnormal, should be followed up with karyotyping.

Should have 2 peaks (for 2 different alleles) - in trisomies, have 3 peaks or increased size of 1 peak.

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Whole exome sequencing

If pt likely to have a single gene defect but normal CMA and no abnormality seen on sequencing likely genes, can do whole exome sequencing.

Includes all exons, ultraconserved regions, regulatory regions, ncRNAs, enhancers, splice donor + acceptor regions.

Will show ALL abnormalities, including normal variants (normally 30,000 per exome):

  • filter out common variants and variants unlikely to have an effect
  • select only the variants in relevant disease genes
  • look at parental genotypes/phenotypes and select variants with relevant inheritance (e.g. de novo, recessive)
  • try and work out which gene is the cause- clinical input required
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