Genes, proteins, and traits

All organisms inherit traits, or observable characteristics, from their parents. Inherited traits can include:

physical features, such as hair and eye coloration; behaviors, such as feeding and mating patterns; and the risk of getting certain diseases, such as heart disease.

Information about inherited traits is found in genes. Genes are pieces of hereditary material that are passed from parents to offspring.

Genes are part of structures called chromosomes, which in eukaryotes are found in the nucleus. A cell typically contains multiple chromosomes, each of which consists of a single, long DNA molecule. Each chromosome also includes proteins called histones that help to organize the DNA. Chromosomes are typically arranged loosely in the nucleus. However, as a cell gets ready to divide after replicating its DNA, its chromosomes coil up and condense into the characteristic “X” shape that we often see depicted in diagrams (including in the one shown below).

DNA is a type of nucleic acid made up of monomers, or subunits, called nucleotides. Four different nucleotides (often called bases) compose DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). The nucleotides in a DNA molecule are connected in a specific order.

The genes that make up an organism’s hereditary material are actually specific stretches of nucleotides within the DNA molecule of a chromosome. Each chromosome in the cell contains many genes.

The cell uses the information found in genes to build other molecules, primarily proteins. Proteins are molecules that perform many different functions in a cell. For example, proteins are involved in defense, storage, transport, cellular communication, movement, and maintaining cell structure.

Proteins are made up of monomers called amino acids. These monomers are connected in long chains to form polymers called polypeptides. Each protein is made up of one or more polypeptides, which are folded and coiled into a specific three-dimensional (3D) structure. This 3D structure determines the protein's function.

So, how does the cell turn the information in genes into proteins? Specifically, the order of nucleotides in a gene determines the order of amino acids in one or more proteins. This means that variation in the order of nucleotides in a gene can produce variation in the order of amino acids in a protein, which can affect the protein’s function.

An organism has many different genes, and so can produce many different proteins. These proteins carry out a variety of functions that, in turn, affect the organism’s traits.

Leopards and some of the cats known as black panthers are the same species (Panthera pardus), but they differ in their coat color trait. Leopards have a golden coat with black markings, while black panthers have a black coat.

In these cats, the coat color trait is influenced by the MC1R gene, which encodes the MC1R protein. The MC1R protein is a receptor located on the surface of cells responsible for producing melanin—the pigment that gives color to animals’ skin and hair. When the MC1R receptor is activated, it triggers cells to produce eumelanin, which is a dark form of melanin. The more eumelanin produced, the darker the skin or hair color.

Leopards and black panthers have different variations in the MC1R gene, and therefore different versions of the MC1R protein. In black panthers, the MC1R protein is highly active, resulting in a higher production of eumelanin and a darker coat. In leopards, the MC1R protein is less active, resulting in the golden coat color trait.

In summary, an organism’s genes determine the structure and function of its proteins. These proteins in turn carry out functions in the cell that influence an organism’s traits.

In fact, it is the variation in genes among different organisms that leads to the vast diversity of life on Earth, as each unique genetic makeup leads to distinct physical and behavioral characteristics.