PubMed · 4714971
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H Lehmann. 1973. Recent developments in globin structure.. https://doi.org/10.1136/jcp.26.5.389-b
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In fungi, most mitotic recombination and at least some meiotic recombination appear to stem from a process of double-strand break repair. During this repair, recombination occurs by conversion caused by the process of double-strand gap filling, by conversion related to heteroduplex formation where homologous molecules interact by complementary base pairing, and by crossing-over which is probably an occasional byproduct of the repair process. From a review of the genetic and biochemical data and the published models of the process of recombination, the following view emerges: broken ends may be acted upon by nucleases and helicases to produce a recombinagenic end which may have both 3' and 5' single-stranded tails. These postulated split-ends may then act independently to find regions of homology with which to react. Invasion by both ends forms two splice-junctions which prime DNA synthesis towards each other to replace lost information, using the homologous sequences as templates. This process would lead to a structure which consists of a double Holliday junction which may be resolved endonucleolytically, sometimes giving a crossover, or by another means such as the action of topoisomerase, to dissolve the structure without a crossover having been formed.
The sex gene SRY has recently been characterized after years of research during which the candidate genes HY and ZFY were excluded. SRY does have all the characteristics expected of the sex gene: it is located on chromosome Y of all mammals, including man; it is specifically expressed in male gonads during early embryonic development mutations and deletions have been found in 46,XY women with gonadal dysgenesis; the Sry gene is present in the vast majority of XX men and finally, transgenic experiments in the mouse have shown that Sry reverses the sex of XX mice. All this demonstrates that SRY is truly the sex gene, but some abnormalities of sex determination in humans remain shrouded in mystery. There are 46,XX men who do not carry the sex gene, and some 46,XX SRY positive true hermaphrodites in whose gonads ovarian and testicular tissues coexist. Finally, SRY is apparently normal in the majority of pure gonadal dysgenesis.
The purpose of this study was to examine the effect of extremely low frequency (ELF) magnetic fields on the induction of genetic damage. In general, mutational studies involving ELF magnetic fields have proven negative. However, studies examining sister-chromatid exchange and chromosome aberrations have yielded conflicting results. In this study, we have examined whether 60-Hz magnetic fields are capable of inducing mutation or mitotic recombination in the yeast Saccharomyces cerevisiae. In addition we determined whether magnetic fields were capable of altering the genetic response of S. cerevisiae to UV (254 nm). We measured the frequencies of induced mutation, gene conversion and reciprocal mitotic crossing-over for exposures to magnetic fields alone (1 mT) or in combination with various UV exposures (2-50 J/m2). These experiments were performed using a repair-proficient strain (RAD+), as well as a strain of yeast (rad3) which is incapable of excising UV-induced thymine dimers. Magnetic field exposures did not induce mutation, gene conversion or reciprocal mitotic crossing-over in either of these strains, nor did the fields influence the frequencies of UV-induced genetic events.