A chromosome is a thread-like structure made up of DNA and proteins. It is found in the nucleus of cells in plants and animals, including humans. Each chromosome consists of a single molecule of DNA tightly coiled around proteins called histones, which support its structure. The term "chromosome" comes from the Greek words for color (chroma) and body (soma) because they are strongly stained by certain dyes used in research.
- Chromosomes are not visible in the cells nucleus, even under a microscope, when the cell is not dividing. However, during cell division, the DNA that makes up chromosomes becomes more tightly packed and is then visible under a microscope.
- Humans have 23 pairs of chromosomes, for a total of 46. Of these, 22 pairs are autosomes (non-sex chromosomes) and look the same in both males and females. The remaining pair is the sex chromosomes, which determine the individual's biological sex. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
- Each chromosome has two short arms (p arms), two long arms (q arms), and a centromere that holds the arms together at the center. The location of the centromere on each chromosome gives it its characteristic shape and can be used to help describe the location of specific genes.
- The unique structure of chromosomes allows DNA to be accurately copied during cell division, ensuring the proper functioning of organisms.
