Mitochondrial and nuclear variants in a U.S. black population: origins of a hybrid population.

The maternal transmission of mitochondria in higher eukaryotes makes it possible to distinguish between reciprocal matings, since offspring possess the mitochondrial DNA variants received from the mother. This possibility can be extended to hybrid populations, the mitochondrial frequencies reflecting the relative maternal contributions from the parental populations. Nuclear variations reflect the relative genetic contributions of the parental populations, irrespective of parental sex. The U.S. Black population is a hybrid of West African and European populations. The African-European matings that contributed to the present Black population are traditionally considered to have been almost exclusively between African females and European males. We have studied nuclear and mitochondrial variants in a sample of U.S. Blacks, comparing them with published frequencies from African and Caucasian groups. Our results suggest that the mitochondria of present-day American Blacks are derived from Caucasians to an extent similar to nuclear genes. In contrast to traditional beliefs, the contribution from Caucasian females is of the same magnitude as that from Caucasian males.

New approach to the localisation of phaeochromocytoma: imaging with iodine-131-meta-iodobenzylguanidine.

Thirty eight patients with known or suspected phaeochromocytoma were studied by radioisotope imaging after intravenous administration of iodine-131-meta- iodobenzylguanidine (131I- mIBG ), a radiopharmaceutical which has affinity for chromaffin tumours. Seventeen positive results (including one false positive) and 21 negative results (including two false negatives) were obtained. Clinical accuracy was 92%. Urinary noradrenaline concentrations were raised in all patients with confirmed phaeochromocytoma. These findings show that 131I- mIBG is of value in localising and assessing the extent of chromaffin tumours.

Serum protein synthesis by somatic cell hybrids.

Serum protein synthesis by rodent hepatomaa x fibroblast, hepatom a x teratocarcinoma, and hepatoma x hepatoma somatic cell hybrids was analyzed by Laurell (rocket) and crossed immunoelectrophoresis. With the hepatoma x fibroblast hybrids, of the nine serum proteins investigated, only transferrin was synthesized by the hybrids (with the exception of one hybrid clone which made albumin). Rat hepatoma (MHC) x mouse teratocarcinoma hybrids did not synthesize transferrin, but one of three clones did produce albumin. Rat hepatopma (Faza) x mouse hepatoma (Hepa 1) hybrids synthesized reduced amounts of albumin and transferrin, compared with the parental hepatoma cell lines. From these studies transferrin synthesis appears to be under different controls from the other serum proteins examined.

Human transferrin C: the sequence and cystine bridges of the N-terminal region.

Human transferrin c (76,000 molecular weight) can be cleaved by cyanogen bromide and separated by gel filtration into 4 fractions, CNBr I, II, III, and IV. CNBr II, the smallest cystine containing fragment, can be separated further into 2 fragments of approximately 3,000 and 9,000 daltons by performic acid oxidation; the smaller fragment is the N-terminus of Tf C. The sequence of both fragments, their relationship to each other through cystine bridges, and their relationship within the whole transferrin molecule is given.

The impact of induced mutations on human populations.

The major impact of an increase in genetic damage will be expressed as an increase in autosomal dominant and X-linked traits as well as chromosomal disorders. The present incidence of dominant traits has been estimated at 1% of live births, but recent data from British Columbia indicate the true value in that population may be an order of magnitude lower. These estimates are important if one measures the damage in terms of doubling dose. Neither the average mutation rate nor the number of loci capable of mutating to dominant detrimental form is known. Mutations that cause sterility or early embryonic loss are detrimental in the Darwinian sense but have little impact on society. Mutations that are more fit biologically may be a heavy burden to society if the affected persons require medical or institutional care. Since exposure to some mutagens is unavoidable, these factors must ultimately be included in a cost-benefit analysis.