What are the major developments in classification systems over the past 2500 years?

During the early period, people were not able to similarize or differentiate between the characteristics of different organisms. In 1758 Carl  Linnaeus proposed a binomial nomenclature system. every single organism was given two names, i.e., genus and species. He then grouped genera into families- orders-classes-phyla-kingdoms. He also identified Animalia (animals) and Plantae (plants) kingdoms. 
Thomas Whittaker proposed a "five kingdom" system in which three kingdoms were added to the animals and plants: Monera (bacteria), Protista, and Fungi.
Carl Woese proposed a radical reorganization of the 5 kingdoms into 3 domains. 

Heatamount of salt . . .

the answer to the blank provided is “an autosomal gene that is required for the expression of genes on the x chromosome”.

testis-determining factor, abbreviated as td, which is more popularly known as sex-determining region y or sry protein, is a dna-binding protein or  gene-regulatory protein/transcription factor, encoded by the  sry gene. it is the gene responsible for the initiation of male gender determination in humans.