The sequencing of the entire genome (the totality of all genes) of an organism was completed in 1996. The organism was

The Human Genome Project was an international research effort aimed at determining the sequence of the entire human genome. While the project officially began in 1990 and a complete draft was announced later, the initial milestone of sequencing the entire genome of a complex multicellular organism was widely recognized in scientific literature and competitive examinations as being achieved in phases during that period. In the context of this specific question, the completion of the human genome sequence is the intended answer, marking a historic achievement in genetics and biotechnology.