Gene transfer in Drosophila melanogaster: genetic transformations induced by the DNA of transformed stocks

'Hertwig Effect' in plants: induced parthenogenesis through the use of irradiated pollen

Studies of four combinations of Nicotiana involving four species, N. langsdorffii (N. l.), N. alata (N. a.), N. glutinosa (N. g.) and N. tabacum (N. t.), have shown that parthenogenetic haploid and diploid maternal individuals may arise with the use of male gametes (pollen) treated with high doses of ionising radiation in plants, similar to that found in animals ("Hertwig Effect'). At lower doses (10-20 Kr) rapidly diminishing numbers of seedlings were produced and many of these died soon after germination or before reaching maturity. In the intraspecific combination N. l. × N. l., viable seeds were produced only at the lower doses of 10 and 15 Kr. In the interspecific combination N. l. × N. a., at lower doses, all plants that came to bloom showed variable hybrid morphology. There were no plants resembling the female parent. In the combination N.t. × N.a., at lower doses there were rare surviving plants which were maternal dihaploid (1 plant out of 4 at 15 Kr) or tetraploid N. tabacum (all 5 plants at 20 Kr). All surviving plants at higher doses (50 and 100 Kr) were maternal tetraploids. In the combination N.t.×N.g., plants produced at lower than 20 Kr were almost all either aneuploid or triploid hybrids. Dihaploid, maternal N. tabacum plants appeared at 20 Kr and higher doses. After 50 Kr the large proportion of plants produced were maternal dihaploid or tetraploid N. tabacum.

Genetic transformation in chicken by the use of irradiated male gametes

Genetic transformation for egg and feather colour hs been obtained in the whole animal, chicken, by the use of irradiated male gametes. In this technique recipient females are first inseminated with irradiated semen from the donor and 24 h later are reinseminated with unirradiated, normal semen of the recipient strain. The transformed progeny are identical to the female strain but for one or a few genes derived from the irradiated semen. The expression of the transferred gene is irregular and may occur either in the first generation, after insemination with irradiated semen, or may occur in the following backcross generation. It is suggested that integration of a normally recessive, transferred gene at non-homologous sites in the recipient chromosomes might affect not only its regularity of expression but also its dominance relationship with the original maternal gene, "releasing" it from the dominance of the latter. The technique potentially offers a rapid method of improving an already established strain of an animal.

Recombination of recessive upsilon+ transformants in Drosophila melanogaster

Recessive transformants (col) obtained fromv(vermilion) embryos treated withv+DNA are shown to map at 1−0·02, a position not distinguishable from that ofsu(s) (suppressor-of-sable) and in agreement with observations indicating phenotypic allelism ofcolwithsu(s) mutants. Recombination in they–col–gtsegment of theXchromosome, over a total map length of O·3 units, was studied among the progeny ofcolv1/y1gtE6cvv1fandy1colgtE6cvv1f/v1females. The data from both crosses exhibit the following features: (1) recovery of reciprocal recombinants betweeny1andcol; (2) recovery of reciprocal recombinants betweencolandgtE6and (3) striking negative interference in they–col–gtsegment. These results allow three alternative interpretations: (1) that recombination in they–col–gtsegment results from conventional crossing-over, with high coincidence of crossovers in the two subsegments; (2) that it results from symmetrical gene conversion at thecolsite (coltocol+, andcol+tocol), which may be accompanied by single cross-overs in either of the adjacent regions; (3) thatcolbehaves like a transposable element, formally symbolizedsu(s)+·col, and that recombination insu(s)+·col/su(s)+(i.e.col/col+) heterozygotes results from transposition of thecolelement from homolog to homolog, accompanied sometimes by crossing-over, either in they–colsubsegment or in thecol-gtsubsegment.