Genotype vs. Phenotype

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By aaron

In biology, 2 terms that are often confused are the terms "genotype" and "phenotype". Let's look at what each of these terms means and how they are different.

The genotype of an organism is the actual genetic code contained in the organism's DNA. The phenotype, on the other hand, is the collection of outward characteristics and traits of an organism, including physical structure, flower or eye color, biochemical characteristics, and even behavior. For example, I have blond hair. Somewhere in my genome is the code to create blond hair. That gene is part of my genotype, while the blond hair itself is part of my phenotype.

The distinction is important, because genotype is not the only factor that determines an organism's phenotype. Phenotype can also be influenced by environmental conditions. A good example of this is the way plants grow differently depending on the environment. For example, if you have a tree sapling and keep it in a dark location, it grows very long and thin, because it is trying to find a source of light. But if you take that same tree and move it outside in full sun, the trunk starts to grow thicker and stronger. It is the same tree with the same genotype (Author's note: I misspoke here. See the comments.), but the phenotype has changed based on its new environment.

Other organisms like animals and humans also adapt to environmental conditions. For instance, if you have ever noticed yourself eating more in the winter than you do in the summer time, that is your body-- your phenotype-- adapting to the different energy demands of each environment. You have the same genotype, but your phenotype has changed based on the environment. The ability of an organism to change its phenotype in response to its environment is called phenotypic plasticity.

In addition to environmental conditions, the phenotype of an organism can also be influenced by what are known as epigenetic factors. Epigenetics is a complex subject, and a full discussion of it is outside the scope of this lecture, but the basic idea is that a particular genetic code can be expressed differently depending on structural changes to the DNA while leaving the actual DNA sequence unchanged. For example, by attaching certain molecules to the DNA strand, a cell can turn genes on or off to affect whether or not that gene is expressed. Importantly, these changes can then be inherited by other cells descending from that cell. If you have ever wondered how one cell can give rise to a complex human being, that's how it happens. A very general type of cell called a stem cell turns into a more specific type of cell, such as a muscle cell. That muscle cell then contains epigenetic factors that dictate how the genome is expressed, so that when it divides, it continues to form new muscle cells. Different genes within the genome are being turned on or off the affect the phenotype of that cell. So even though the cells in my brain have the exact same genome as the cells in my liver, they have very different phenotypes because of epigenetic factors.

So, to recap, the genotype of an organism is the actual genetic sequence contained by the organism's DNA, while the phenotype of an organism is its collection of outward traits and characteristics that are the result of the genotype as well as other environmental and epigenetic factors. #science #biology #genetics #cell biology #microbiology #DNA

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