Hemoglobins A and A2 in New World primates: comparative variation and its evolutionary implications

A frameshift addition causes silencing of the delta-globin gene in an old world monkey, an anubis (Papio doguera)

A delta-globin gene of an anubis, Papio doguera, was cloned, and the nucleotide sequence of a region of about 2,000 bp including the gene was determined. In comparison with that of pSP3, a delta-globin clone from the gene library of a normal Japanese, the anubis delta-globin gene showed one base addition in the second exon at the codon for amino acid 55, generating a termination codon at the new 59th codon. The other differences found in the region analyzed were not considered to affect expression of the delta-globin gene. Therefore, it was concluded that this frameshift addition was at least one of the causes of silencing of the delta-globin gene in the anubis. In addition, from the sequence divergence in the delta-globin gene, the period of this silencing was estimated to be at most 4 million years, and the divergence of anubis occurred at most 30 million years ago.

Delta thalassemia: a non-deletion defect

Hematological and gene mapping studies of two Southern Italian children doubly heterozygous for delta 0-thalassemia and delta 0 beta 0-thalassemia have been carried out. No HbA2 was detectable by electrophoresis of total hemoglobin in these patients. Restriction enzyme analysis of the globin gene cluster with delta, gamma, epsilon and RIH cloned probes showed all the expected normal bands, in addition to the abnormal fragments related to a previously described type of delta 0 beta 0-thalassemic deletion, demonstrating an apparently intact globin gene cluster on the thalassemic chromosome. The relevance of this finding to models for coordinated expression of non alpha globin genes is discussed.

Silent delta-globin gene in Old World monkeys

The delta polypeptide chain is present in the adult hemoglobin of all higher primates except Old World monkeys. Because Old World monkeys have evolved from higher primate ancestors, it can be concluded that the ability to synthesize this polypeptide has been lost relatively recently. It is shown here that the gene for delta globin exists in two of these species, the rhesus monkey (Macaca mulatta) and the baboon (Papio papio). Restriction endonuclease fragments of monkey genomic DNA bearing the delta- and beta-globin genes were detected after hybridization of human globin cDNA probes to filter-bound primate DNAs according to the Southern method. A restriction map prepared for rhesus DNA was identical in overall organization to the map of the human region. This indicates that large deletions or additions of DNA are not responsible for the Old World monkeys' lack of delta globin.

Variation in hemoglobin A2

The structure, properties and function of, and some biosynthetic and genetic aspects of, Hb A2 are described. The structural variants of Hb A2 are reviewed and their geographical distribution presented. Hb A2, Hb A2-Flatbush and Hb A2-Babinga are characteristic of negro populations and may have originated in Western or Central Africa. Hb A2-Sphakia is characteristic of Canadian Amerindian and Hb A2-Indonesia of Indonesian/Malay populations. Hb A2-NYU has only been found sporadically and most frequently in persons of Eastern European origin. The other three variants of Hb A2 have only been reported in a single person or in single families. Some conditions which are associated with changes in Hb A2 levels are reviewed.

A study of baboon hemoglobin

Electrophoretic analysis of hemoglobin types of 409 baboons of various species, mostly from Senegal, corresponds with the findings of other authors. Baboon hemoglobin is homogeneous as a whole, but differs electrophoretically from that of other monkey species. However, a difference in the electrophoretic mobility of the nonhemoglobin fraction of Papio anubis and Papio cynocephalus suggests a possibly different amino-acid sequence. This information may be useful for the classification in doubtful cases.

On some principles governing molecular evolution

THE FOLLOWING FIVE PRINCIPLES WERE DEDUCED FROM THE ACCUMULATED EVIDENCE ON MOLECULAR EVOLUTION AND THEORETICAL CONSIDERATIONS OF THE POPULATION DYNAMICS OF MUTANT SUBSTITUTIONS: (i) for each protein, the rate of evolution in terms of amino acid substitutions is approximately constant/site per year for various lines, as long as the function and tertiary structure of the molecule remain essentially unaltered. (ii) Functionally less important molecules or parts of a molecule evolve (in terms of mutant substitutions) faster than more important ones. (iii) Those mutant substitutions that disrupt less the existing structure and function of a molecule (conservative substitutions) occur more frequently in evolution than more disruptive ones. (iv) Gene duplication must always precede the emergence of a gene having a new function. (v) Selective elimination of definitely deleterious mutants and random fixation of selectively neutral or very slightly deleterious mutants occur far more frequently in evolution than positive Darwinian selection of definitely advantageous mutants.

Silent hemoglobin alpha genes in apes: potential source of thalassemia

Small quantities of unusual hemoglobins were found in 1 of 37 chimpanzees and 2 of 6 gorillas. In each genus these hemoglobins contain unique alpha chains that differ from the ordinary by eight to nine scattered amino acid changes. The unusual chains arise from a hitherto undetected hemoglobin (3)alpha locus. No (3)alpha products are found in most apes; accordingly, (3)alpha is considered synthetically inactive in all but a few reversion mutants. Indirect evidence that the inactive (3)alpha locus is juxtaposed to an active alpha locus together with the supposition that (3)alpha exists in man provides a setting wherein thalassemia might be produced by nonhomologous recombination between two loci.