Many mutations in the bithorax gene are known, such as postbithorax, contrabithorax and bithoriaxoid. Each mutation has a different effect on development of the reduced wing-like T3 appendage, the haltere. None of these mutations occurs in the coding sequence of bithorax, instead, where are these mutations and how do they effect development?
◦ These mutations alter the slice sites for bithorax and affect the splicing of the bithorax mRNA. Their different effects on development are cause by affects on alternative splicing.
◦ Each mutant alters a different codon within the bitorax gene, which affects the DNA-binding behavior of the bithorax protein.
◦ These mutations each effect silent sites and effect the stability of the bithorax mRNA.
◦ Bithorax is inhibited by zygotic genes from the mother and these mutations affect maternal genes.
◦ These mutations each effect a different enhancer(s) near the bithorax gene and the resulting misexpression of bithorax in each mutant causes patterning defects in the haltere.
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