At various times it has been proposed that the size of the gene can be estimated from experiments on the yield of mutations obtained with known doses of X-rays. The assumptions involved in calculations of this sort are discussed, and some of the objections which have been raised against them answered. It is pointed out that similar assumptions, applied to experiments on the inactivation of enzymes and viruses, lead to estimates of the sizes of these bodies correct to a factor of two in diameter. The estimate arrived at for the size of the gene inDrosophila is 4–8 mμ diameter. The length of the euchromatic region of theX-chromosome thread in the sperm is deduced to be 10–20 μ.
Volume 100, 2021
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