Aspects of the distribution of HbS in the United States.

Frequencies of HbS obtained by several screening clinics are analyzed for age, sex, and location effects. All seem to be present in some form, though age and sex effects may be conditional on location. An attempt is made to elaborate the common observation of increasing frequency with age. This is shown to be the result of differences in fertility favoring the normal. A simulation which includes 25% admixture was done. The results indicate a genetically relevant New World experience for the population to be about 9--12 generations with the heterozygote having fitness of 0.96--0.99.