Archived | Laboratory Orientation and Testing of Body Fluids and Tissues for Forensic Analysts | Typing

The ability to draw inferences as to the origin of semen in a sexual assault case is obvious. The power to do this in traditional serology was limited, and depended mainly on ABO and PGM typing. The PGM₁ locus is expressed in semen and vaginal secretions, and the methodology and interpretation used in its typing are exactly the same as for blood.

ABO typing is somewhat different. Almost everyone has at least trace levels of antigen in their body secretions that correspond to their ABO blood type. However, about 80% of the population has very high levels of these antigens in body secretions. These persons are described as secretors. The remaining 20% of the population are described as non-secretors and have concentrations of the antigens that are too low for normal detection. The quantitative difference is genetically determined. The gene responsible has two alleles, a dominant form, Se, and a recessive one, se. Thus SeSe and Sese persons are secretors and sese persons are non-secretors.

The A, B, and H antigens are polysaccharides. They are found on RBC surfaces as lipo-polysaccharides and in secretions as glycoproteins. The biochemical genetics involves four genes as shown in the table below.

Biochemical Genetics
Gene	Expression	RBC genotype	Secretions genotype
Le, H and secretor	Dominant H allele in presence of dominant Se allele converts Le^a substance to mixture of H, Lea and Le^b substances	Depends on A and B alleles	Le^aand Le^b substances present together with A and/or B depending on A and B alleles
Le, ABO A allele together with H and Se	A blood group, Lewis a and b	A, H, Le(a-b+)	Le^a, Le^b , A, H
Le, ABO B allele together with H and Se	B blood group, Lewis a and b	B, H, Le(a-b+)	Le^a, Le^b , B, H
Le, ABO O (silent) allele together with H and Se	O blood group (No A or B blood group), Lewis a and b	H, Le(a-b+)	Le^a, Le^b , H
Le, H and sese	A, B or H depending on ABO gene	A. B. H depending on ABO gene, Le(a+b-)	Le^a only
Le, hh and Se	no ABH or Lewis	No ABO activity (Bombay phenotype)	Le^a only
lele, H and Se	ABO depending on ABO gene alleles, no Lewis	A, B, H (depending on ABO alleles), Le(a-b-)	A, B, H (depending on ABO alleles), no Lewis
lele, H and sese	A, B, or H depending on ABO gene	A, B, H depending on ABO gene, Le(a-b-)	No ABH, no Lewis
lele, hh and Se	No ABH or Lewis	No ABO activity (Bombay phenotype) Le (a-b-)	No ABH, no Lewis
Note: Secretors all have an Le allele, an H allele and an Se allele. For simplicity, AB heterozygotes are not listed in the Table – they will have A and B.

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Date Created: June 28, 2023