Evening star., 1950-08-16
Genetic Changes Likely
In Atomic Bomb BIust
Theories Revised of Effect
Of Reduction on Heredity
By Thomos r. Henry

Recent experiments have forced con-
siderable revision Of theories on human
heredity as to the effects of radiation.
such as would be received In the neigh
borhood Of an atomic bomb blast.
The Atomic Energy Commission has
revised the sections dealing with this in
its recent report on the effects of
atomic weapons.
Tests with mice, for example, have
shown that immediate effects on the
next generation can be greatly reduced
II exposed individuals do not beget off,
spring for three months or more after
exposure. 1t is probable that the same
applies to human beings, although very
little actually is known about human
heredity. 1t may, or may not, follow
the same laws as in lower animals. There
is q high probability, however, that it
Is quite similar.
Affected Two Ways.
There are two ways, it is explained,
In which heredity is affected by radia-
ton. The units Of heredity are sub
microscopic particles known as genes.
They are arranged in bundles, the
chromosomes, and the particular ar
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extent the way in which the individual
genes function.
Gamma rays, or x-rays, may break
up or alter the arrangement of a
chromosome. In this case the effect
often Is seen in the next generation.
1t is known as dominant" Generally
the changes are for the worse. They
may result in death of the embryos or
Of
fective individuals. In extremely rare
cases they are for the better. These
chromosome breakups occur infre-
quently in nature.
But, the mouse experiments show,
apparently the chromosomes have a
tendency to rearrange themselves into
normal patterns so that there is very
little effect on heredity after a few
months.
The other effect is much more subtle
and difficult to follow. 1t is a direct
effect Of the radiation on the individual
genes. This generally results in what is
known as a recessive. Before any effects
become apparent it is necessary that
both parents should have the same type
OF defective gene, probably due to a
chemical change. The receSsive is hand
ed down from generation to generation
without showing any effect until two
such parents come together. There may
be no change for many generations The
effects Of an atomic bomb blast might
appear after more than a century.
OF Recessive Type.
The mouse experiments indicate that
delaying .parenthood would have no
hof he
of such recessives.
1t has been generally accepted that
the vast majority of gene changes are
OF the recessive type. But, according to
the revised report Of the Atomic Energy
Commission, dominants whose influence
will be apparent in the next generation
are considerably more likely than has
been supposed. This happens if the in
jured gene happens to be in the so-called
"sex chromoSome" which male offspring
receive only from their mothers.
"1n the face of a large number of
gaps in our knowledge" says the COM
missions report, ''it is hard to arrive at
meaningful practical recommendations.
An important point has emerged from
our experimental work. There is large
body of data which indicate that any
dose of radiation, no matter how small.
increases the probability of genetic
changes. Until recently the risk would
have been thought to apply mainly to
distant descendants. But new informa-
ton on the frequency of partial domi-
nants indicates that the risk may not
be negligible even to the first genera
tion."
The great bulk of information on
heredity has come from studies on fruit
flies, where effects may be traced
through several generations in few
months. But, the report reveals, recent
experiments have shown that the like
lihood of chromosome breaks is consid-
erably greater in mice than in fruit flies,
and the same should almost certainly
apply to man.