Chromosomes are thread-like structures found in the nucleus of almost every cell in our body. They are made up of DNA, which is tightly coiled around proteins called histones. The DNA molecule is packaged into nucleosomes, which then coil up tightly to create chromatin loops. The chromatin loops are then wrapped around each other to make a full chromosome. Each chromosome has two short arms (p arms), two longer arms (q arms), and a centromere holding it all together at the center. The DNA making up each of our chromosomes contains thousands of genes.

Chromosomes are not visible in the cell’s nucleus 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 (46 in total), with one set coming from each parent. Of these 23 pairs, one pair are sex chromosomes, which 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 of our chromosomes are sections of DNA called telomeres, which protect the ends of the chromosomes during DNA replication by forming a cap. Without the unique structure of chromosomes, DNA molecules would be too long to fit inside cells. Chromosomes give our cells the actual instructions to make us into a unique person.