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.
Many human diseases are caused by mutations in single genes
“Bad,” “neutral,” and “good” mutations.
Comparison of two pairs of rII mutations
Mutations causing defects in pattern formation in Drosophila
Variable penetrance of mitochondrial mutations
Point Mutations