Chromosomal structure refers to the organization of DNA within a chromosome, which is a thread-like structure found in the nucleus of eukaryotic cells. Each chromosome is made up of DNA tightly coiled around proteins called histones, forming a complex known as chromatin. This structure allows for efficient packaging of genetic material, ensuring that DNA can fit within the cell nucleus. In humans, there are 23 pairs of chromosomes, totaling 46. Each chromosome contains many genes, which are segments of DNA that code for specific proteins. The arrangement and number of chromosomes are crucial for proper cell function and inheritance, as seen in genetic disorders like Down syndrome, which is caused by an extra copy of chromosome 21.