If an autosome is present in only one copy at conception, that individual will not develop to term. Yet human males have only one copy of the X chromosome and they do develop normally. Why is there a difference?

An autosome requires two copies so as to maintain the chromosome number in the human species where one is from the father and other from the mother.

While the x chromosome is a type of sex chromosome which determines our sex. The x chromosome encodes feminine characters while the y encodes masculine characters.

It only changes the body by a little bit and so a single copy is enough.The basic anatomy and morphology of a male and female is more or less same with subtle changes such as broader hips of women and the hoarse voice of men.While the autosomes determine other important features such as blood group type immunity, eye colour etc.Thus two copies of it are required

The difference lies in the genetic mechanism of sex determination. In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). Essential genes on the X chromosome are typically present in two copies in females, providing redundancy in case of mutations. In males, although they have only one copy of the X chromosome, they also have a Y chromosome which carries genes necessary for male development. This genetic compensation allows males to develop normally despite having only one copy of the X chromosome.