Molecular aspects of blood grouping

Question 1

Describe the immucor bioarray beadchip method

Answer 1

1. coloured bead each labelled w/ diff probe
2. isolate genomic DNA from blood & PCR
3. ds DNA -> ssDNA by exonuclease
4. perform elongation rxn in bead chip array: ssDNA, thermo sequenase, Fl-labelled dCTP, unlabbeleld dNTP
5. ssDNA binds to probe. If there’s a mismatch at the 3’ end of probe = no extension (bc polymerase not have proofreading ability)

Question 2

When might you choose GENOTYPING over phenotyping by serology (8-9)

Answer 2

• pt has a recent transfusion: phenotype may be MF
• Chronic transfusion e.g. B-thal or sickle cell
• phenotype the father to determine RHD zygosity in baby (e.g. if dad homo = baby is hetero, if dad hetero = baby has 50% chance of being hetero)
• foetal testing from cell-free foetal DNA in mum’s plasma
• discriminate b/w weak vs partial D Ag expression
• predict extended phenotype of patient’s RBC
• typing for Ag w/ no reagents e.g. Dombrock
• Screen for rare Ag
• can detect partial Ag expression

Question 3

When might you choose SEROTYPING over genotyping

Answer 3

• formation of hybrid genes due to recombination of chromo.

Question 4

if mum was weak D or partial D do they need prophylactic anti-D?

Answer 4

• Weak: no bc considered D pos since express the D Ag (though at small [ ])
• Partial: yes bc considered D neg since express diff D Ag to normal (so normal D Ag considered foreign = make Aby)