Types of Influences on Phenotypes

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll look at different factors that affect phenotype. We'll examine how genetics and environmental factors can change how DNA is expressed, as well as modifications to the DNA by other molecules, such as epigenetic changes.

What Is a Phenotype?

Have you ever heard you have your mother's eyes? Or your father's nose? Do you share hair color, or skin color with your siblings? These characteristics are a product of genetic inheritance, or inheriting DNA from your parents. The DNA you inherit changes your traits, which we call your phenotype. Different combinations of genes produce different phenotypes.

However, it's not just the batch of DNA you inherit that controls your phenotype. There are other factors as well. Today, we're going to first look at the basics of how DNA controls your traits, then look at more complicated scenarios, like environmental influences.

Genetic Influences

Every trait, or characteristic, of your body is controlled by at least one gene. Genes come in different ''flavors'' (forms) called alleles. For example, there's an allele, or a version of a gene, for hair texture that gives you curly hair. There is also an allele for straight hair. You get one allele from each parent for any given trait. So, you might inherit an allele for curly hair from your mom, and an allele for straight hair from your dad. The combination of alleles you get determines your phenotype for that trait.

However, some phenotypes are more complicated. They use a pattern called epistasis, where one gene controls the expression of another in a pathway. For example, skin color in humans is determined by multiple genes in an epistatic pattern. There is one gene that is necessary to start any production of pigment in the skin. Many other genes control pigment production, but the first gene is like a master switch. If people inherit a mutant copy of that gene, no matter what other genes they have, they won't make any pigment and will be albino. Their phenotype is influenced by multiple genes, but one gene acts like a master switch for controlling the rest of the assembly line for pigment production.

Baldness acts as an epistatic gene which controls the production of any hair despite the genes inherited for color

Environmental Influences

By now, you probably understand that genotype controls our phenotype, and you would be completely correct. But, there are also environmental factors that can shape our phenotype. Let's take a look at two examples.


Although the sun can feel great on a cool day, too much sun is bad for your skin. The Sun's ultraviolet (UV) radiation can change the structure of your DNA, creating mutations. UV radiation makes parts of your DNA stick together, changing the message, the proteins made, and ultimately your phenotype. With too many changes to the DNA, a person can develop a tumor, or uncontrolled cell growth, and eventually cancer. This change in phenotype (healthy to cancerous) was inflicted by environmental factors like exposure to ultraviolet radiation.

Mutations in DNA can change the phenotype of an organism
UV light


The environment doesn't just cause structural changes in DNA. It can also cause changes in how DNA is expressed in the cell in a process called epigenetics. In epigenetics, certain environmental triggers cause the cell to add modifications to the DNA. One modification is called methylation. They attach a special compound called a methyl group that causes the cell to interact with that piece of DNA differently, causing changes in gene expression.

Methylation is one mechanism of epigenetics

Another way epigenetics happens is through modification of proteins that help coil up and store the DNA, called histones. These changes affect how easily DNA can be accessed to be read in the cell. Normally DNA is wound around the histones and must be unpacked to be expressed, like unpacking boxes from your closet in order to use the items stored in them. If the histones are changed, it affects how easily you can get to the DNA, just like if you changed the type of storage system in your closet, it might be harder or easier to get to your things.

There are also small pieces of a different molecule called RNA. Some RNA molecules, can cause interference with genes, preventing them from being expressed. These RNA molecules are different from the ones the cell uses to make protein.

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