This expression is more clearly seen after germband retraction. In the later stages of embryogenesis, the expression can be detected not only in the nervous system and the gonads, but also in the hindgut, the anal pads and the Malpighian tubules. In ovarioles, there is a high level of expression in nurse cells of the developing egg chamber, and transcripts are detectable starting from around stage 6 in oogenesis. Upon oocyte maturation, the transcripts are transported into the egg cell, and high transcript levels can be detected in the unfertilized egg. Effects of Mutation or Deletion Mutations in the twins locus causes mitotic abnormalities during early embryogenesis and late larval development in an allele-specific manner.
Homozygotes have small brains and die during late pupal stages.
These individuals probably survive to late developmental stages due to the presence of a maternally provided wild-type product. There is a range of mitotic abnormalities during metaphase and anaphase in third-instar larval neuroblasts. The abnormal metaphase figures are characterized by excessive chromosome condensation, low level of polyploidy, and in some cases, the presence of irregular chromatid condenstion. These abnormal phenotypes are probably not due to the absence of functional spindles, since anaphases can be easily found in these brains. However, most anaphases appear abnormal.