CO2 Sensitivity in Drosophila (sigma factor)

Maternal Effects and Cytoplasmic Inheritance
Maternal effects
Cytoplasmic Inheritance Involving Dispensable Hereditary Units
Kappa particles in Paramecium
CO2 Sensitivity in Drosophila (sigma factor)
Organellar genetics 
Plastid inheritance : variegation in plants
Male sterility in plants
Chloroplast genetics Non-chromosomal genes in Chlamydomonas
Mitochondrial genetics
Paternal inheritance of cpDNA and mtDNA
Most Drosophila flies, can be subjected to a contact with pure CO2 for long hours, without injury. L'Heritier and Teisser (1958), however, discovered a true breeding strain of Drosophila which was sensitive to CO2. The sensitive flies, when exposed briefly to CO2 for a short period, become unconscious in a characteristic way, with their legs becoming paralysed. When reciprocal crosses were made between CO2 sensitive and normal strains, it could be shown that the trait was inherited only from female parent. In other words, while sensitive mothers always give sensitive progeny, sensitive fathers only rarely give sensitive progeny if the mother is normal. In rare transmission through male also, sensitivity is quickly lost after first generation. It has also been shown that if an extract obtained by crushing sensitive flies, is injected into the body of wild (normal) flies, sensitivity can be induced. It was also shown that this sensitivity can be attributed to a virus like particle called sigma found in cytoplasm of the cells of a sensitive fly.

Sigma factor is transmitted through egg cytoplasm and its reproduction depends on initial supply and on suitable temperature of 20°C, because it is heat labile at high temperature. It does not need a specific gene and may be found associated with different genotypes. A sensitive fly retains its sensitive trait, even when all its chromosomes are replaced by those of normal fly, suggesting that sigma factor or particle is located in cytoplasm and has properties of non-chromosomal genes or plasma genes. Some physical characteristics of sigma are also known. It seems to be a particle of 0.07 micron in diameter, and contains DNA responsible for its hereditary nature.