A chromosome is a thread-like structure located inside the nucleus of animal and plant cells. It is made up of protein and a single molecule of deoxyribonucleic acid (DNA) . DNA is tightly coiled many times around proteins called histones that support its structure. The unique structure of chromosomes keeps DNA tightly wrapped around spool-like proteins, called histones. Without such packaging, DNA molecules would be too long to fit inside cells. Each chromosome has two short arms called p arms and two long arms called q arms, and a centromere holding it all together at the center. The location of the centromere on each chromosome gives the chromosome its characteristic shape and can be used to help describe the location of specific genes. Humans have 23 pairs of chromosomes, one set comes from the mother and one set comes from the father. Of these 23 pairs, one pair are sex chromosomes, so they differ depending on whether you are male or female (XX for female or XY for male). The other 22 pairs are autosomes (non-sex chromosomes) and look the same for both males and females. At the ends of each chromosome are sections of DNA called telomeres, which protect the ends of the chromosomes during DNA replication by forming a cap.