Notes

What does it mean when someone says "It must be in your genes"? Genes make up everything that is you, from physical characteristics, like your hair color, to your chemical makeup, like how efficient your metabolism is. These characteristics that make you, you, are called traits, which is defined as a genetic characteristic of an individual. A gene is defined as a segment of DNA that contains the information for making proteins. They allow the nucleus to run the cell's activities and carry hereditary traits.

Chromosomes carry many genes, and the number of genes in a cell is far greater than the number of chromosomes. Each gene is located in a specific place on a chromosome called a locus. Genes are responsible for inherited traits and are units of coded DNA that pass physical, chemical, and behavioral characteristics from parents to offspring.

In many cases, one trait is determined by several genes. Skin pigmentation, for example, is influenced by many genes. In other instances, a single gene can determine a trait like freckles or earlobe shape. It is even possible for a single gene to influence more than one trait. The mutated gene for phenylketonuria (PKU) interferes with the conversion of the amino acid phenylalanine into tyrosine. This single mutated gene can result in mental disabilities, thin hair, and decreased skin pigmentation.

The relationship between DNA, genes, and chromosomes can be confusing, so it may help to think of DNA as a book. A book is a collection of words and the nucleotides represent words in the DNA book; these words can be arranged in many different ways to create sentences. Similarly, nucleotides can be sequenced in many different ways to create genes that represent sentences in the DNA book. Sentences in a book are collected to form chapters, and each chapter contains many different sentences. Chromosomes represent chapters in the DNA book.