The human body is a construction of different molecules, but it is proteins that determine many of the fundamental aspects of how each person physically looks. Proteins rely on another important element of development known as DNA, which acts as the hereditary material for almost all living things.
DNA, or deoxyribonucleic acid, is found in nearly every cell in the human body. Most of the DNA resides in the nucleus of a cell, known as nuclear DNA, and other smaller parts located in organelles, like the mitochondria of the cell known as mitochondrial DNA. It’s DNA that tells the cell what function it will play in the body. Each DNA molecule is made in the shape of what scientists refer to as a double helix. Within this structure are rungs represented by letters that make up the four-letter DNA alphabet. These letters include A for Adenine, C for Cytosine, T for Thymine and G for Guanine. Each rung is made up of two letters, with A always pairing with C and T always pairing with G. These DNA strand letters come together to create words and sentences known as genes.
A gene is comprised of a specific length of DNA, and acts as an instruction manual for making the different proteins in the body. One strand of DNA contains several different genes. Genes need a specific structure of letters in order to create normal proteins. However, it’s not uncommon for genes to change or mutate, which can lead to abnormal cell growth and function. Your unique combination of genes is called your genotype. Genes combine together to create traits.
Each person has a different combination of genetic traits that creates an individual’s look, and may also influence behavior and risks for disease. Traits that impact how a person looks are called physical traits, which include features like hair color, height, body shape and skin or eye color. Your unique combination of traits is called your phenotype.
Dominant Recessive Traits
How you look depends on the genes you inherited from your parents. You have two copies, called alleles, one from your mother and one from your father. Each gene, or trait, is either dominant or recessive. As the name suggests, dominant traits overpower the recessive ones. In terms of eye color, for example, brown eyes are dominant over blue eyes. That means that if you inherited a gene for brown eyes from your father and a gene for blue eyes from your mother, you will have brown eyes. The only way for you to have blue eyes is you inherited the gene for blue eyes from both parents.
Dominant recessive traits are ones that, while recessive, are more common. For example, it is more common to not have freckles than to have them. That means that it is more likely we will inherit the “no freckles” gene from each parent and, therefore, keep passing them on. Many people don’t know that the gene for having six fingers on each hand is dominant over the gene for five fingers. However, most people have five fingers. That means that the dominant gene for six fingers, while dominant, is simply not as common.