Phenotype

In genetics, a phenotype is the set of things we can see and observe in a living thing, like its shape, size, color, and how it behaves. These observable traits include everything from the physical look of an organism to how it grows, its body processes, and even actions like a peacock's display.

An organism's phenotype comes from two main sources: its genes, which are like instructions inside it, and the world around it. The environment can change how these genes show up, leading to different traits. For example, Labrador Retriever coloring shows up as yellow, black, or brown, depending on both genes and conditions.

The idea of separating what is inside an organism (its genes) from what we see (its phenotype) was suggested by Wilhelm Johannsen in 1911. This helps us understand the difference between what is passed down through generations and what we can actually observe in living things.

Definition

The term phenotype describes all the things we can see or measure in a living thing, like its shape, how it grows, and even its actions. This includes both the body’s form and its behaviors. For example, human blood groups are part of a person’s phenotype.

The idea of a phenotype comes from how genes work together with the environment. What we see in an organism isn’t just from its genes, but also from the world around it. This mix shapes everything from physical looks to how a creature behaves.

Phenotypic variation

Phenotypic variation is very important for evolution by natural selection. Not all changes in what an organism looks like or how it acts come from differences in their genes. Living things can change based on their environment. This means that the whole organism, not just its genes, works with the world around it to shape what traits it shows.

The way genes and what an organism looks like or does work together is often shown as a simple idea: genes plus environment equals what we see. But really, it's more complicated because the organism itself plays a big part in how genes and the environment work together. Sometimes, what an organism looks like can change a lot depending on where it lives. For example, a plant called Hieracium umbellatum grows differently on rocky cliffs compared to sandy dunes along the coast of Sweden. Even with the same genes, the plant changes its shape and leaves based on its surroundings.

Sometimes, small random changes happen in how an organism develops. In Drosophila flies, for instance, the number of tiny parts in their eyes can differ between the two eyes of the same fly.

The idea of what an organism shows can also include things that affect others around it. For example, a beaver builds dams, changing its environment, which shows the effects of its genes. This is part of what scientists call the "extended phenotype."

Genes and phenotypes

Phenotypes develop from the interaction between genes and the environment around them. For example, an albino appearance can happen when a change occurs in a gene linked to melanin creation. Even then, things like UV radiation can affect how much melanin is made.

How much certain genes are active can change what traits an organism shows. If a gene that makes an enzyme is very active, the organism might show one trait; if it’s not very active, it might show another. Many things, like what an organism eats or stresses it faces, can change how genes act and affect its traits.

Phenome and phenomics

Not to be confused with Phoneme or Phonology.

A phenotype includes all the things we can see in a living thing, like its shape or how it behaves. The word phenome is sometimes used to talk about a group of these traits all together. Studying this group is called phenomics. This helps scientists understand how genes affect these traits and can explain things like health or how well a living thing can survive.

Phenomics is useful in farming too. It can help find genes that make plants strong against dry or hot weather. In the future, phenomics might help doctors choose the best medicine for each person based on their own traits.

Large-scale phenotyping and genetic screens

See also: Genetic screen and Essential gene

Scientists use special tests to study how changes in genes affect an organism's traits. These tests help us learn what genes do. Many of these studies use tiny living things like bacteria, such as E. coli and others, because it's easier to change their genes.

Recently, scientists have also used these tests with animals, like mice, to study behaviors and other traits that are not fully understood. For example, they looked at how changes in genes affect learning, memory, daily rhythms, vision, how animals handle stress, and reactions to certain substances.

These experiments involve mice whose families were treated with a chemical that causes changes in their DNA. The mice are then watched closely to see any changes in their behavior. These changes help scientists find new genes and understand how they work.

These studies have shown that changes in a specific gene can affect vision and even lead to problems in the eyes of mice. Interestingly, the same change in a similar gene can cause vision problems in people, showing how studying animals can help us understand and possibly treat human health issues.

Evolutionary origin of phenotype

The RNA world is an idea about how life might have started on Earth. It suggests that tiny molecules called RNA came before cells existed. These RNA molecules could make copies of themselves.

The shape of the very first RNA molecule that could help make more RNA would have been the first phenotype. The order of building blocks in that RNA molecule would have been the original genotype.