What is the significance of the 23rd chromosome pair in humans?

The 23rd chromosome pair plays a crucial role in determining the sex of an individual. In humans, this pair consists of either two X chromosomes, which results in a female (XX), or one X and one Y chromosome, which results in a male (XY). This distinction is essential for sexual differentiation and the development of primary and secondary sexual characteristics during growth.

The other choices do not accurately describe the significance of the 23rd chromosome pair. For instance, the age of an individual is not determined by chromosomes, but rather by biological processes and the passage of time. Blood type is determined by genes located on different chromosomes, specifically the ABO and Rh blood group genes, and not by the sex chromosomes. Genes involved in immunity are spread across various chromosomes, not confined to the 23rd pair. Thus, the defining function of the 23rd chromosome pair is its role in determining sex.