DEOXYRIBONUCLEIC ACID REPLICATION IN MEIOSIS OF CHLAMYDOMONAS REINHARDI .I. ISOTOPIC TRANSFER EXPERIMENTS WITH A STRAIN PRODUCING 8 ZOOSPORES

DNA replication in meiosis of Chlamydomonas reinhardi has been studied by 15N density-labeling experiments coupled with cytological observations. It has been shown that (1) during zygotic maturation, there is neither chromosomal DNA replication nor meiotic division; (2) during zygo-spore germination, meiosis occurs, and the first meiotic division is preceded by a single chromosomal DNA replication; (3) the replication of chromosomal DNA associated with meiosis is semiconservative; (4) only hybrid chromosomal DNA molecules are detected at the end of zygote germination, when eight zoospores emerge from each zygote, indicating that only one DNA replication occurs in the entire period between the mating of gametes and the germination of zygotes; (5) a DNA component (M-band DNA) replicates extensively and appears in large quantity during zygote maturation.