D. E. Lea
Articles written in Journal of Genetics
Volume 39 Issue 2 January 1940 pp 181-188
It is known experimentally that the efficiency of production of sex-linked lethal mutations in
Volume 43 Issue 1-2 January 1942 pp 189-210
1. Neutrons produce qualitatively the same types of chromosome aberrations as X-rays, but more of all types of aberration are produced, per ionization, by neutrons.
2. The ratios of the dose of X-rays to the dose of neutrons both measured in roentgens, required to produce equal numbers of aberrations are 2-4 for chromatid breaks, 3-6 for isochromatid rejoins, 4-5 for chromosome breaks, and from 10 to 5, at the doses used, for interchanges.
3. Many of the interchanges produced by neutrons are caused by single ‘hits’, that is by single ionization paths.
4. Neutrons and X-rays do not differ in any effects that they may have on the rejoining process.
5. The results are attributed to the greater number of primary breaks, and their different distribution, when they are produced by the denser ionization paths of neutron radiation.
6. It must be inferred that more than one ionization is needed to break a
Volume 44 Issue 2-3 December 1942 pp 216-245
Volume 45 Issue 2 October 1943 pp 186-196
1. The coefficients of chromatid breakage (compare Table 4) are highest with Ag
2. This is interpreted to mean that only the densely ionizing ‘tails’ of the electron tracks are effective in chromosome breakage, and that the ‘tails’ have a higher efficiency only where they traverse the chromatid; for the track of an Al
3. The probability of survival of chromatid breaks is the same in the pollen-tube nucleus as in the pollen-grain nucleus.
4. The two chromatids of a chromosome are in contact 24 hr. before metaphase in the pollen-grain nucleus. They are slightly separated 15 hr. before metaphase in the pollen-tube nucleus.
5. The probability of interchange in the pollen-tube nucleus is reduced by the different method of packing of the chromosomes in a long cylindrical nucleus as compared with the spherical one of the pollen grain.
Volume 47 Issue 1 July 1945 pp 1-9
The rate of X-ray induction of dominant lethals in the sperm of the Oregon-R stock of
The rate of depression of the sex ratio of females to males, founded on our own and other data, is about 2·5% per 1000 r.
Volume 47 Issue 1 July 1945 pp 10-24
The suggestion is put forward that radiation-induced recessive lethals, or a large proportion of them, are due to chromosome breaks. About one-third of all the chromosome breaks primarily induced by the radiation are lethals. If the break restitutes, a lethal unaccompanied by chromosomal aberration (type A lethal) results. If the break takes part in chromosome interchange a type C lethal, which is associated with chromosomal structural change, results. Arguments are given against the alternative position-effect explanation of type C lethals.
A quantitative theory of dominant lethals is developed on the basis that the dominant lethals are a mixture of single breaks which fail either to restitute or to interchange but instead undergo sister-union, and of non-viable chromosomal structural changes involving two or more breaks. The experimental curve of variation with dose of the yield of dominant lethals is successfully fitted, and also the curve of the yield of viable structural changes.
It is shown that the recessive lethal and the dominant lethal theories are consistent in that they require the same postulated number of primarily produced chromosome breaks per unit dose (namely, 0·75 breaks per sperm per 1000 r.). Experiments on the distortion of the sex ratio in the progeny of irradiated males with ring-shaped or rod-shaped
Volume 47 Issue 1 July 1945 pp 25-40
Volume 47 Issue 1 July 1945 pp 41-50
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 in
Volume 47 Issue 2 January 1946 pp 113-136
Volume 47 Issue 2 January 1946 pp 137-149
Volume 48 Issue 1 April 1947 pp 1-10
A theory is given of the process of chromosomal structural rearrangement following irradiation. The theory applies to nuclei in which the union of breakage ends is at random, and assumes that the number of breaks primarily produced is proportional to the dose.
Formulae and tables are given enabling the proportion of nuclei undergoing eucentric and dyscentric types of rearrangement respectively to be calculated as a function of the dose, the cases of nuclei with 1, 2, 3, 4, 5, or many chromosome, arms in the set being separately considered. The five-arm calculation is compared with published experimental results of the irradiation of the spermatozoa of
Volume 49 Issue 3 December 1949 pp 264-285
Statistical calculations are made of the distribution numbers of mutants in a culture of bacteria in which the number of mutants increases on account both of new mutations and of division of old mutants. In this way the largely qualitative conclusions of Luria and Delbruck are extended and placed on a firm quantitative basis. The results of these calculations, which enable the mutation rate to be inferred from experiments with parallel cultures, are presented in the form of tables. Statistically efficient methods of using these tables are discussed.
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