Were more boys Essay

This essay has a total of 827 words and 4 pages.


were more boys





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
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