Final answer:
The X and Y chromosomes are referred to as sex chromosomes, distinguishing them from autosomes, which constitute the remaining 22 pairs of chromosomes that determine most inherited traits. The Y chromosome, much smaller than the X, contains the SRY gene which is crucial for male development.
Step-by-step explanation:
X and Y chromosomes are called sex chromosomes to distinguish them from the other pairs of chromosomes, which are called autosomes.
Humans have 22 pairs of autosomes and one pair of sex chromosomes. The autosomes are involved in determining most of a person's inherited traits, while the sex chromosomes largely determine an individual's sex and related traits.
In humans, females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). Although the Y chromosome allows for pairing during meiosis due to a small region of similarity with the X chromosome, it is much shorter and contains far fewer genes.
While most genes on the X chromosome are unrelated to sex, there is one gene on the Y chromosome, the SRY gene, which triggers the development of male characteristics. Females, having two X chromosomes, have one that is often inactivated to form what is known as a Barr body, to ensure a balance in gene expression between the sexes.