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QUANTITATIVE PCR DATA FALSIFY THE CHROMOSOMAL ENDOREDUPLICATION HYPOTHESIS FOR VOLVOX CARTERI (VOLVOCALES, CHLOROPHYTA)
Author(s) -
Kobl Iris,
Kirk David L.,
Schmitt Rüdiger
Publication year - 1998
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1046/j.1529-8817.1998.340981.x
Subject(s) - biology , endoreduplication , genetics , dna replication , cell division , gene , genome , pre replication complex , origin of replication , microbiology and biotechnology , cell , ploidy
Two conflicting hypotheses for chromosome replication in the Volvocaceae, one postulating multiple rounds of replication prior to cell division (endoreduplication) and the other claiming a canonical sequence of one round of nuclear DNA replication preceding each cell division, have been tested experimentally. Competitive PCR of the single‐copy actin gene (target) of Volvox carteri f. nagariensis Iyengar and a shortened gene version (competitor) containing the same primer binding sites were used to assess the genome equivalents present in a given number of cells. Determining the molar ratio of the PCR products generated from target DNA (extracted from a known number of cells) and defined numbers of competitor molecules revealed that Volvox embryos between the one‐ and 16‐cell stages possess an average of between one and two—but never more than two—copies of the actin gene. This led us to conclude that the number of genome equivalents per nucleus in dividing Volvox embryos varies only between one and two and that, unlike the case predicted by endoreduplication, the nuclear genome undergoes only one round of replication prior to each cell division.