H. LehmannR. CaseyA. LangR. StathopoulouK. ImaiS. TuchindaP. VinaiG. FlatzUniversity of CambridgeMahidol UniversityMedizinische Hochschule Hannover (MHH)2018-04-192018-04-191975-01-01British Journal of Haematology. Vol.31, (1975), 119-13113652141000710482-s2.0-84990439389https://repository.li.mahidol.ac.th/handle/20.500.14594/10823In Haemoglobin Tak two normal α‐chains are combined with two β‐chains elongated by 11 residues beyond the C‐terminus. Unlike in the α‐chain abnormal Hb Constant Spring, the elongation cannot result from a point mutation of a stop codon. It is probably due to an unequal crossing‐over near the 3′ end of the β‐chain structural gene. This could cause either a deletion of the normal stop codon or a shift in the reading frame. Oxygen dissociation of purified Hb Tak shows no cooperativity but in Hb A + Tak haemolysates there is no interaction between the two above 40% O 2 saturation. Heterozygotes for Hbs A and Tak show an imbalance of globin chain synthesis (α/non α= 1.5), the synthesis of β Tak resembles that of the β‐chain in β + thalassaemia. Copyright © 1975, Wiley Blackwell. All rights reservedMahidol UniversityMedicineArticleSCOPUS10.1111/j.1365-2141.1975.tb00905.x