Were More Boys Or Girls Born To

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Were More Boys Or Girls Born To Atomic-Bomb Survivors? Essay, Research Paper Were more boys or girls born to atomic-bomb survivors? Normally, somewhat more pregnancies terminate in boys than girls in all populations, and this normal preponderance of male births has not been demonstrated to be significantly altered when the parents (one or both) were exposed to atomic radiation. However, when the genetic studies began, it was believed that a person’s gender was simply determined. Individuals inheriting an X chromosome from their father and one from their mother were destined to be females; whereas those individuals who inherited a Y chromosome from their father and an X from their mother would be males. Thus, females would have two X chromosomes and males only one. These

notions suggested, in turn, that when mutations induced in the X chromosome by ionizing radiation are incompatible with survival (are lethal), their expression would be manifested differently in the two genders and would depend, partly, upon whether the X chromosome was inherited from the mother or the father. More specifically, since a father was thought to transmit his X chromosome exclusively to his daughters, if a lethal mutation were present on the X chromosome in the father’s sperm, it would find expression only in his daughters. Whereas, since mothers transmit their X chromosomes equally to their sons and daughters, a lethal mutation might find expression in either sex. If the mutation were dominant, i.e., expressed itself if only one copy was present, the two sexes

would be affected equally often; however, if the mutation was recessive (normally requiring two copies for expression), since the male has only one X chromosome, it would invariably manifest itself in males, but in females, manifestation of the new mutant would occur only if the second X chromosome fortuitously carried a functionally similar gene. It follows that since the likelihood of a mutation would increase as dose increased, if the father were exposed, more female embryos would be lost, and at birth, the frequency of males would be greater than would be true if the father were not exposed. If, on the other hand, the mother were exposed, more male embryos would be lost, and at birth, the frequency of males would decrease. If both parents were exposed, the resulting

proportion of male births, would be related to the individual parental doses and the frequency of dominant versus recessive lethal mutations. As can be seen, this theory of sex determination made fairly specific predictions that could be compared with the actual observations that were accumulating. When the data from the initial study were examined, it appeared that the frequency of male births was, in fact, declining with dose when the mother was exposed, and increasing, albeit modestly, with increasing paternal dose. The rate of change with dose was not, however, statistically significant, although in the direction predicted by theory. It was for this reason that when the clinical phase of the studies ended, data on the sex ratio continued to be collected on the supposition

that the rate of change might become statistically significant with further information. To this end, observations on the frequency of male births were continued through 1966, when information was available on 140,542 births of which 73,994 were to parents one or both of whom were exposed. However, when these additional observations were analyzed, the results did not support the earlier findings; indeed, the modest changes seen were opposite to those predicted by theory. Today, the earlier arguments regarding sex determination are known to have been overly simplistic. First, they did not take into account the occurrence of X chromosome aneuploids (errors in X-chromosome number), such as the Klinefelter and Turner syndromes, which might confuse the determination of the gender of