Practice question

Lack of Sex-lethal protein in Drosophila abolishes female splicing program. In XX embryos without Sxl, its own transcript retains male exon 3 containing early stop codon producing no functional protein, transformer transcript splices to truncated male form, and doublesex splices to DsxM isoform promoting male differentiation, pigmentation and sex combs. Additionally dosage compensation defaults to male mode causing hypertranscription of X chromosomes via MSL complex, often lethal for hyperdiploid XX individuals. Consequently chromosomally female flies develop morphologically as males, proving Sxl as necessary master female switch.