What type of chromosome determines sex characteristics in an organism?

The correct choice here is the sex chromosome, as these are the specific chromosomes that play a direct role in determining the sex of an organism and the associated characteristics. In many species, including humans, there are two main types of sex chromosomes: X and Y. The combination of these chromosomes typically dictates an organism's sex. For example, having two X chromosomes typically results in a female, while having one X and one Y chromosome typically results in a male. Beyond just determining the sex, these chromosomes also carry genes that can influence secondary sex characteristics, such as the development of different body structures and functions related to reproduction.

Autosomes, on the other hand, are chromosomes that are not directly involved in determining sex; they carry the majority of an organism’s genetic material and traits unrelated to sex. Somatic chromosomes refer broadly to non-germline cells that make up the body of an organism and can include autosomes but do not specifically indicate their role in sex determination. Lastly, the centromere is a part of a chromosome that plays a role in cell division by ensuring proper segregation of chromosomes but does not influence an organism's sex characteristics.