Background Early marriage is not uncommon in Ethiopia, particularly for adolescent girls in rural settings. Social norms are among the factors believed to perpetuate early marriage practices. This qualitative study explores social norms surrounding adolescent girls’ marriage practices in West Hararghe, Ethiopia. Methods This study used the qualitative inquiry method to explore social norms in rural Ethiopia. Focus group discussions were conducted with purposively sampled married and unmarried adolescent girls, adolescent boys, and parents. A total of 158 individuals participated in the study, comprising 95 adolescents and 63 parents. Data were collected using locally developed vignettes. A thematic framework analysis approach using the Social Norms Analysis Plot (SNAP) was employed to diagnose and understand social norms. Results Adolescent girls’ marriage was found to be mainly influenced by their peers who conform to prevailing social norms. Marrying one’s first suitor was considered an opportunity not to be missed and a symbol of good luck. Relatives, neighbors, and marriage brokers facilitate adolescent girls’ marriage in accordance with the local social norms. Girls usually accept the first marriage proposal regardless of their age, and they are highly expected to do so by their peers, parents, and influential others. Exceptions from the early marriage social norm include adolescent girls determined to continue their education and those having supportive teachers. Conclusions In this study context, social norms strongly encourage early marriage and are mainly perpetuated by peers of adolescent girls and influential adults. A strong determination to continue education on the part of girls, strong school performance, and supportive schoolteachers are important conditions for circumventing social norms on early marriage. As social norms evolve slowly, we recommend periodical assessment in order to develop locally appropriate interventions against early marriage.

Antisera to a DBA2 lymphoma (SL2) were raised in C57 black mice. The sera contained cell-dependent antibodies which lysed SL2 cells in conjunction with a monolayer of adherent peritoneal cells from unimmunised mice. The strongest lytic reaction was observed when the three components of the system, monolayer, target, and antiserum, were incubated together. The free antibody was not cytophilic for macrophages. It combined specifically with the target cell but precoated SL2 cells were not lysed effectively, probably because cells in the monolayer also accelerated the inactivation of antibody on the surface of the target cell.

This paper describes a technique for studying the effect of alkali on the denaturation of high molecular weight DNA from mammalian cells. The method has been used to measure the length of DNA that unwound and separated from its complementary strand under different denaturing conditions. The results provided an estimate of the minimum size of the DNA in the cell nucleus.

A method for labelling newly replicated DNA in tissues of a rat is described. Rats were infused with a mixture of bromodeoxyuridine and [3H]-thymidine. After the animal had been killed and the different tissues extracted, the heavy newly replicated DNA could be separated from the light parental DNA on a density gradient of CsCl.

1. Sedimentation in gradients of alkaline sucrose has been used to observe the production and rejoining of X-ray-produced strand breaks in the DNA of cells from rats and chickens. The DNA was estimated by a fluorimetric method which permitted the study of non-dividing cells whose DNA could not be labelled with radioactive precursors.

This paper describes a technique for quantitatively measuring both the number of interstrand cross-links and the number of strand breaks introduced into the DNA of cells by a drug. The method has been illustrated by studying the effect of nitrogen mustard on the DNA of a murine lymphoma cell (L5178Y). The results have been compared with measurements of the molecular weight of DNA in alkaline sucrose gradients.

The size of the replicating units of the DNA from the murine lymphoma cell L5178Y has been studied by direct measurement of the size of the growing DNA strands in sucrose gradients. Cells were pulse-labelled with [3H]thymidine and then irradiated with low doses of X-rays in order to introduce a small amount of fragmentation into the DNA, thus overcoming entanglement effects. Detailed analysis of the radioactivity profiles obtained on sedimentation of the resulting labelled DNA fragments in alkaline sucrose gradients has provided information about the size of the growing DNA strands. The results suggest that most of the replicating units have a single-strand molecular weight of about 2 · 108. Sometimes a much smaller population with molecular weight of about 4 · 107 is also observed. On completion of replication the newly-synthesized strands are linked end-to-end, so that the molecular weight of the DNA strands in the G2 phase of the cell cycle is greater than 109 (i.e., larger than can be estimated by the methods available at present).

Alkaline sucrose gradients have been used to study denatured DNA from a murine lymphoma cell. The results show that the sedimentation behaviour of DNA molecules of number-average molecular weight above 1 · 108 is dependent on the speed of centrifugation. This means that this method cannot be used to measure high molecular weights. The results also cast doubt on the recent claim that a structural subunit can be isolated from the DNA of a mammalian cell (J. T. Lett, E. S. Klucis and C. Sun, Biophys. J., 10 (1970) 277; M. M. Elkind, C. Kamper, Biophys. J. 10., (1970) 237.

X-irradiation introduces single-strand breaks into the DNA of cells. After irradiation, cells rejoin these strand breaks. In L5178Y cells, it was found that this process did not require DNA, RNA or protein synthesis.

The production of X-ray-induced double-strand breaks in the DNA of murine lymphoma cells (L5178Y) has been measured by determining the molecular weight of the DNA from X-irradiated cells. The cells were lysed on top of neutral sucrose gradients and the molecular weight of the released DNA was measured by rate sedimentation through the gradients. Several independent criteria have been used to test whether the sedimenting DNA was pure and unaggregated and to show that the sedimentation behaviour of the DNA provided a true measure of its molecular weight. These criteria were only fulfilled if the speed of centrifugation was less than 20 000 rev./min. Using these conditions, the results show that double-strand breaks are formed in the DNA of L5178Y cells as single events with an efficiency of 2900±400 eV per break, and that after X-ray doses of more than 20 krads these breaks are not rejoined on post-irradiation incubation. Under appropriate conditions DNA molecules of molecular weight up to 2·109 sediment freely and the molecular weight of DNA from unirradiated cells is at least 3·109 and probably greater.

The radical yield of cyclohexane, γ-irradiated at 77°K has been compared with the radiation chemical yields of the major products—dimer and trans-vinylene unsaturation. It was found that the radical—dose curve was not linear and consisted of a low dose linear region partially saturating to give a high dose linear region. The dimer-dose curve was found to follow the radical curve with the yield approximately half the radical yield over the whole dose range used whereas the unsaturation-dose curve remained linear over the dose range employed. The implications of these results have been discussed.

TSUKADA et al.1 have recently reported that, after denaturation, newly replicated DNA from regenerating rat liver cells apparently has a lower molecular weight than the main body of the chromosomal DNA. After pulse labelling with tritiated thymidine, they isolated the DNA by conventional methods, which extensively shear the DNA, thereby reducing its chain length, and then measured the molecular weight of the denatured DNA by sedimentation on an akaline sucrose gradient.

ESR spectroscopy has been used to study free radical formation and reactions in frozen aqueous solutions of DNA, thymidine and thymidylic acid, γ-irradiated at 77 °K. ESR spectra were recorded at 77 °K immediately after irradiation and after warming to higher temperatures. The effect of added cystamine was also investigated. Our results suggest that the paramagnetic species stabilized on DNA and the thymine compounds at 77 °K are anions. The well known thymine radical appeared either after warming the samples to 195 °K or after post γ-irradiation with ultraviolet light. Added cystamine reduced the thymine radical concentrations. Our results are consistent with the postulate that the thymine radical in irradiated DNA is not formed by the direct addition of a hydrogen atom to the thymine ring but is formed by proton transfer to the thymine anion.