What is the best definition of a virus

A virus is a microscopic infectious organism that has the ability to recreate/replicate itself with nothing but the cells that are living in another organism. Viruses have the ability to infect anything, from plants to animals to humans. You have much more of a chance of this being fatal (to any of these life forms) if you have heart problems or vitamin deficiency.

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.