Even your talents and personality are at least partially determined by the genetic code that you carry in every cell of your body. Each cell contains almost 200 meters of DNA strands which are organized and packaged into chromosomes. The human nucleus contains 46 chromosomes. Each chromosome is a partner in a pair, so that there are 23 pairs of homologs. The remaining pair of chromosomes are known as the sex chromosomes.
Females posess two X chromosomes which look exactly alike and code for the same traits.
Males posess an X chromosome and a Y chromosome which look different and code for male traits. When the cell is not dividing, the chromosomes unwind. When a cell needs to make a particular protein, the portion of the chromosome which codes for that protein unwinds completely, so that the cell has access to the protein's DNA code. Those portions of the chromosome not in use remain tightly coiled and folded. Just before the cell divides by mitosis, each chromosome unwinds completely and a copy of the DNA molecule is made.