Strands of DNA are arranged into different structures, the largest of which are chromosomes. Humans have 23 pairs of chromosomes. One set of chromosomes is inherited from the mother and the other from the father. Certain genetic conditions are caused by extra or missing chromosomes. An example of such a condition is Trisomy 21, more commonly known as Down Syndrome, where a person has three copies of chromosome 21 instead of two.
What are chromosomes?
