<i>Bicaudal</i>, a genetic factor which affects the polarity of the embryo in <i>Drosophila melanogaster</i>

Abstract

Abstract An inherited disturbance in egg polarity has been observed in Drosophila melanogaster. The bicaudal abnormal embryos develop the terminal segments of a second larval abdomen in mirror‐image symmetry to the terminal segments of the normal abdomen. The two abdomens may be symmetrical with four or five segments at each end of the egg or have more abdominal segments at the normal posterior end than at the reversed end. The reversed posterior ends appear to have normal spiracles, hindgut and Malpighian tubules. The bicaudal embryos and two other specific lethal types associated with them are produced in very low frequency. The production of these lethals is associated with an unmarked second chromosome, which has been carried in three separate inbred lines in combination with a Curly, Lobe, speck balancer chromosome. Flies homozygous for the chromosome and flies heterozygous for this chromosome and a second chromosome containing a deficiency at the vestigial locus can produce the syndrome. Reciprocal crosses, of flies of a genotype which can produce the syndrome with flies which do not, have shown that the maternal genotype is the controlling factor in the production of the abnormalities.