Pre-Meiotic DNA Synthesis and Recombination in CHLAMYDOMONAS REINHARDI.

The time of the pre-meiotic S-period was determined by (32)P incorporation in synchronously germinating zygospores of Chlamydomonas reinhardi at six and one-half to seven hours after the beginning of germination. Phenethyl alcohol treatment caused death of zygospores at a period one hour before the S-period, and also during meiotic prophase. Recombination between arg-1 and arg-2 was increased by treatment with phenethyl alcohol or mitomycin C at a time between the first sensitive period to phenethyl alcohol and the S-period. Actinomycin D caused an increase in recombination at the time of this sensitive period. FUdR, nalidixic acid and hydroxurea all cause a decrease in recombination when applied during S-period, and have no effect earlier. These results are explained by postulating (1) that the units of delayed premeiotic replication are whole replicons, and (2) that the amount of recombination is proportional to the number of replicons in which synthesis is delayed. It is suggested that the control of DNA replication controls the distribution of recombination events.