Dimethylnitrosamine and diethylnitrosamine, two potent carcinogens, are nonmutagenic when tested directly in microorganisms. Likewise l-naphthylamine and 2-naphthylamine are also nonmutagenic but the N-hydroxy derivatives are mutagenic in microorganisms. Apparently these compounds require metabolism to breakdown products which are then the proximately active agents, and microorganisms lack the ...

Gene conversion and conversion-associated reciprocal recombination have been studied in various Saccharomyces cerevisiae hybrids. In a sample of 11,023 unselected meiotic tetrads, 907 conversions were observed at the arg4, thr3, his1, and SUP6 loci. Of these conversions, 445 (or 49.1%) were associated with reciprocal recombination of bracketing markers no more than 20-centimorgans apart. For co...

ONVENTIONAL recombination theory has held that genetic recombination occurs after DNA replication, when each chromosome is composed of two chromatids; that crossing over involves a full-chromatid interaction between nonsister chromatids, and yields reciprocal products from breakage reunion events; and that either no crossing over occurs between sister chromatids, or if it occurs it is unrelated...

rather novel mechanism for crossing over based on BELLING’S ideas A (1933)-was suggested by LINDEGREN and LINDEGREN (1937) and its implications were thoroughly discussed by SCHWARTZ ( 1954). It was proposed that crossing over of the usual type (between nonsister strands) takes place between only two of the four chromatids, presumably the newly synthesized ones. In order to explain the occurrenc...

During the first division of meiosis, segregation of homologous chromosomes reduces the chromosome number by half. In most species, sister chromatid cohesion and reciprocal recombination (crossing-over) between homologous chromosomes are essential to provide tension to signal proper chromosome segregation during the first meiotic division. Crossovers are not distributed uniformly throughout the...