A Genetic Test for Dose-Response

    X-Ray irradiation of a female Drosophila may induce recessive lethal mutations on one of the two X chromosomes in reproductive cells in her germ line. When mated to an un-irradiated male, some of her daughters will be heterozygous for the X' chromosome with the recessive lethal (X'X). When these X'X daughters are back-crossed to the un-irradiated hemizygous males (XY), half of the male embryos will inherit the unmutated maternal X and half will inherit the lethal X' . The latter males die in early development, thus X'X females will have only half  the expected proportion of male offspring.


X
Y
X'
X' X
X' Y
X
X X X Y


    The dose-response curve of X-ray exposure versus rate of induced mutation is linear, which suggests that there is no lower limit (threshold) of radiation exposure that does not produce some mutagenic effect. Chronic low-level exposure to radiation in other species (including humans) has been implicated in a variety of medical conditions, including cancer.


All text material 2014 by Steven M. Carr