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The Basics of Genetics Before talking about genetics, it is important to define a few critical terms. First of all, genetics as a science consists of the study of heredity and the ways that genes affect a person’s physical and emotional makeup. There are many elements that make up this science, each of which has to be fully understood before grasping their impact on nicotine and smoking risks. Genes are “the units of heredity and are the instructions that make up the body’s blueprint. They code for the proteins that determine virtually all of a person’s characteristics,” explains an online course from the University of Miami Health System. “Most genes come in pairs and are made of strands of genetic material called deoxyribonucleic acid, or DNA .” Humans have access to around 35,000 genes, each of which is combined in unique ways for each person. Another substance, called “ribonucleic acid” ( RNA ), carries instructions from DNA to the cells that control how they grow. The ways that DNA and RNA work in a living body are sometimes referred to as the “genetic code.” A very complex series of gene combinations make a person who they are as an individual. Think of DNA as a computer program—each strand gives a person’s body the instructions necessary for operating and developing. And while most of a person’s DNA code will be shared with others—particularly members of their family—small variations in the DNA can cause major changes in a person. Variations on genes are referred to as alleles . A change in just one allele can impact much about a person. Eye-color alleles, for instance, are single genes that dictate the color and tone of a person’s eyes. The same is true of hair-color alleles. Just a change of a few genes, and a person’s hair is blonde instead of brown. However, a person does not have access to an unlimited amount of genetic code. Instead, they are made up only of what their parents

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Understanding Genetics