Each of the trillions of cells that make up the human body contain 23 pairs of structures called ch...
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Each of the trillions of cells that make up the human body contain 23 pairs of structures called chromosomes. A chromosome is made up of a coil, or double helix of DNA. The DNA provides a complete set of instructions for how our bodies should develop and function. There are also short sets or instructions within the DNA called genes. The mother and father each provide half of the complete set of genes a baby is born with. The genes provide instructions for over 200 different types of cells. A cell needs to know which short set of instructions to follow and which of the parents' genes will be active or expressed. Sometimes the mother's, sometimes the father's, sometimes both, and sometimes neither parental gene is active. Chemical and molecular processes determine which genes are expressed by tagging them for certain functions. Tagging loosens the coil of DNA, which is normally wound tightly around spools of proteins called histones, and would be 40,000 times longer, if unwound. Loosening or slightly unwinding the coil makes the genes accessible so they can make proteins required for the structure, function, and regulation of tissues and organs. Through tagging, genes can be turned on and off, which permits fast adaptation to changes in the environment. During pregnancy, the mother's actions and the environment can influence where the tags go and which genes will be expressed - which can affect the health of the developing baby. Some changes continue throughout life and can be passed down from one generation to the next.