9781422272312

of genes is often a crapshoot, which can be scary to those who are concerned about some types of diseases. For example, the unique physical and mental characteristics of people with Down syndrome are caused when a person has one extra copy of the twenty-first chromosome on their DNA strand. Other conditions, such as sickle cell anemia, are also caused by just one variation in a person’s genetic code. A person’s whole life and health could be heavily affected by their DNA.

The DNA molecule is tightly coiled and packaged inside of the chromosomes. All of a person’s hereditary information, called the genome, is encoded in DNA. The human genome contains about 3 billion nucleotides and about 20,000 genes, which are contained in twenty-three pairs of chromosomes.

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Nicotine and Genetics: The Hereditary Predisposition