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Genetic diversity within and between natural populations of Rattus norvegicus.

The levels of gene diversity for 17 polymorphic loci in natural populations of wild rats were examined for three separate locations in North and South America. The level of gene diversity in the total sample for the RT1.A locus, the dominant class I histocompatibility locus in the major histocompatibility (RT1) complex of the rat, was 0.807. The degree of gene diversity for nonalloantigenic loci scattered throughout the rat genome was 0.215, a level comparable to, if not slightly higher than, that for other mammalian species. The large and consistent levels of diversity for individuals within each population suggest that significant deviations from random mating have occurred within each group. Conclusions from analyzing genetic distance and the index of genetic differentiation between the three populations are consistent with these populations' geographic isolation and small effective population size. Assuming that the separation of the North and South American groups has existed for approximately 300 years, the effective size of these populations is estimated to be approximately 1,500 individuals. Apparent differences in the distribution of the number and frequency of alleles in the major histocompatibility complexes of mice and rats and the level of genetic differentiation among separate rat populations may be due to the effects of genetic drift in small populations.

Daily physiological iron requirements in children.

Median daily iron absorption was determined in iron-replete males and females between 2 and 19 years of age from the upper and lower socioeconomic strata of the Venezuelan population. A comparison was made with iron absorption of well-nourished children, on the basis of hematological and anthropometric reference values from the U.S. The median absorption level, which was calculated from the increase in total body iron due to growth and the daily losses through exfoliation and menstruation, was also used to estimate the requirements of 95% of the population. When the requirements were expressed in terms of body weight, no significant difference in iron absorption was observed between the three Venezuelan and one U.S. groups, ranging from about 30 to 38 micrograms/kg/day in both sexes between 4 and 16 years of age. However, when the requirements were expressed without division by the weight factor, the requirements of the better nourished groups were somewhat higher than those of the Venezuelan lower socioeconomic population with, in addition, a threefold variation over the 5 to 16 year age range. These findings suggest that the total iron requirements of children at a certain age may be most adequately expressed in terms of the optimal body weight for that age.

Comparison of the haplotypes of the major histocompatibility complex in the rat. V. A serological, genetic and numerical study of the RT1.A region antigens.

The classification of the RT1.A phenotypes of a large number of inbred and congenic strains of rats, including those prototypic for all of the known RT1.A phenotypes, was done by examining the reactivity of a variety of unabsorbed antisera with cells of the different strains. The data were analysed by the techniques of numerical taxonomy without reference to the previous classification by the classical serological methods. The most effective way of analysing the data was the use of the Jaccard correlation coefficient and the average linkage method of statistical analysis. Four conclusions were drawn from this study. First, the RT2 antigens must be matched in the donor and recipient pair used to raise the anti-RT1 (MHC) antiserum or spurious typing results can occur due to the presence of anti-RT2 antibodies. Second, using anti-RT1 antisera raised in RT2 compatible pairs of rats, the classification of inbred and congenic strains into the RT1.A phenotypes on the basis of classical serological studies was confirmed. Third, two groups of closely related RT1.A phenotypes were found (a, f, d and b, m). Fourth, the AUG and PVG strains, both of which carry the the RT1.Ac phenotype, are quite distantly related on the basis of this taxonomic analysis and the RT1.Ag and RT1.An phenotypes are the most distantly related compared to all of the other rat strains and to each other. These data provide further evidence that the RT1 polymorphism of the rat is very limited, especially in respect of man and mouse.