What Are Genes?
Distinct stretches of DNA called genes help determine how your body develops over time. Some refer to DNA, or your genetic code, as a blueprint that helps you grow into the unique and distinct individual that you are. Your genes influence everything from how you look, to how you act, and how susceptible you are to disease.
How Exactly Are Genes Related to DNA?
In each and every cell in your body, you'll find a copy of your DNA—half donated from your mother and half donated from your father. And it's there to help guide your body's development and maintenance, ultimately helping to determine your traits like height, eye color, and temperament.
In total the human genome is estimated to contain between 20,000 and 25,000 protein-coding genes. While the terms 'DNA' and 'genes' may sometimes be used interchangeably, they are in fact not exactly the same. A scientist will tell you that a gene is a functional unit of DNA. More simply stated, a gene is a precise stretch of DNA that helps to determine some trait or aspect of your being. It's a unit of hereditary information that's been passed down to you from your ancestors.
What Are Genes Made of?
Simply put, genes are made of a specific length of nucleotides, the repeating units found in DNA. Nucleotides consist of three components: a five-carbon sugar, at least one phosphate group, and a nitrogen-containing base (adenine, cytosine, guanine, and thymine—abbreviated as A, C ,G, and T).
Hydrogen bonds between the nitrogenous bases enable two strands of DNA to form the distinct double helix structure. If you think of DNA as a twisted ladder or a spiral staircase, the base pairs would form the rungs or steps. A single human protein-encoding gene could be as short as just a few hundred base pairs or as long as over two million base pairs.
In popular culture, we often discuss genes as if each gene corresponded to a specific trait. You may have heard of the warrior gene, a particular piece of genetic code that has been linked to more impulsive behavior, for example. But with very few exceptions, a single gene does not offer a program for a single physical feature or disease state. There's no single 'blue-eyed gene' or 'tall gene.' It's not that simple.
Genes contain the biological instructions to help the body build specific molecules. Those molecules, generally proteins, are the building blocks that help construct and maintain your cells, your organs, and your body as a whole. Multiple genes work together, in ways that scientists are still trying to more fully understand, to build and maintain your body and minds. Research has shown that even the simplest traits are affected by many different genes—and a single gene can be involved in the development of multiple traits or features.
Gene Variants or Alleles
Genes have different variations, which are known as alleles. Humans inherit alleles in pairs: you inherit one allele from your mom and one allele from your dad. Each allele pair represents a genotype, which can be described as homozygous or heterozygous. If the pairs of alleles are the same, the genotype is homozygous. If the alleles in the pair are different, the genotype is heterozygous. It is the particular combination of alleles in a genotype that contributes to an organism's distinct, observable characteristics, or phenotype.