[
Methods Cell Biol,
1995]
DNA transformation assays in a whole organism provide experimental links between molecular structure and phenotype. Experiments with transgenic Caenorhabditis elegans start in general with the injection of DNA into the adult gonad. Effects on phenotype or gene expression patterns can be analyzed either in F1 progeny derived from the injected animals or in derived transgenic lines. Microinjection of C. elegans was first carried out by Kimble et al. (1982). Stinchcomb et al. (1985) then showed that injected DNA could be maintained for several generations in transgenic lines. The first selective methods for producing and maintaining transgenic lines were reported in 1986 (Fire, 1986). These methods have been considerably improved since then (Mello et al., 1991) , so that assays involving DNA transformation are now a standard part of the experimental repertoire for C. elegans.
[
Trends in Ecology & Evolution,
1998]
Sexual reproduction is perhaps the greatest of all evolutionary puzzles. It's a puzzle because sexually reproducing species pay the cost of spending half their resources (over and above what is needed for vegetative growth) in producing males, whereas parthogenetic species utilize all their resources meant for reproduction in producing only females (or hermaphrodites) like themselves. This twofold cost of sexual reproduction is sometimes referred to as the twofold cost of producing males. Three advantages of sexual reproduction that might offset this cost have been proposed. Genetic recombination and cross fertilization permit sexually reproducing species to (1) bring together, in the same individual, mutations arising in different individuals; (2) generate genetic variability and thus adapt to changing environments; and (3) shuffle their genes in every generation and thus keep parasites at bay. While evolutionary biologists are busy testing their favourite ideas for offsetting the twofold cost of producing males, recent work by Craig LaMunyon and Samuel Ward shows that a nematode, Caenorhabditis briggsae, appears to have found a way of gaining the benefits of sexual reproduction without paying the cost of producing males.