ABO Gene and Fecundity

ABO B allele is the lowest frequency allele at ABO gene so possible causes of its rarity including that of de-selection of phenotypes of ABO B including lower fecundity is addressed. Although fecundity is only one aspect of selection though an important one, other phenotypes of ABO B may play a role in its frequency in human populations. If ABO B evidences lower fecundity, higher longevity could be a linked phenotype since research supports lower fecundity having a trade-off of higher longevity. A phenotype of lower fecundity and higher longevity could be caused by an allele of a gene in linkage disequilibrium with ABO B. Research on dopamine beta hydroxylase (DBH) and its linkage with ABO supports this. Linkage disequilibrium of ABO B gene with dopamine beta hydroxylase (DBH) low activity gene having higher longevity would be an example of balancing selection supporting ABO B’s survival albeit at a lower frequency than the other ABO alleles. In ob-gyn patients, ABO blood types as a proxy for ABO alleles were compared as to number of pregnancies. The survey was of patients from one physician’s practice in the southeast USA Patients having more than three children were studied since that is above the average fecundity in the USA and thus focuses on higher fecundity to compare as to ABO blood group. The distribution in this population of ABO blood groups was ABO O .44, ABO A .42, ABO B .09, ABO AB .05. Thirteen patients had both known ABO blood type and were of greater than three parity. ABO O type was present in five of these patients, ABO A in seven patients and ABO AB in one patient. Though the study is quite limited by the small number of subjects, the lower fecundity of ABO B was suggested and raised the question of what counterbalancing linked genetic mechanisms like DBH low activity may be supporting survival of ABO B allele. The answer to this question increases knowledge of what phenotypes ABO gene and genes in linkage disequilibrium to it codes for.