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Evolution describes the slow changes species go through to better survive in their environment. Small changes are always occurring naturally when an organism reproduces. When an animal has a baby, that baby is a combination of its mother's and father's genes, and probably also has some small changes that neither parent has. When a bacterium divides in two, the two resulting bacteria can have small genetic changes called mutations. These changes are always occurring between generations in a species.
What is Evolution
Here I will describe evolution in bacteria. When it comes to talking about evolution, bacteria are the easiest organism to understand. Bacteria reproduce by division (binary fission), where they make a single copy of their genome then each new cell takes one copy of the genome. When a bacterium divides small changes called mutations are introduced into the new bacterial DNA. These mutations can (but don't always) change how the bacterium behaves.
Mutations sometimes affect how the bacterium behaves. Let's imagine three mutations that can affect the bacteria in a population. The first type of mutation we call a neutral mutation. Neutral mutation: A mutation that does not affect the fitness of the organism. During evolution this type of mutation has little to no effect on the species. Some mutations don't have any effect on the organism, these mutations are called silent. The second type of mutation is called a deleterious mutation. Deleterious mutation: A mutation that affects the organism in a bad way. This type of mutation makes an organism less fit to survive. The third type of mutation is called a beneficial mutation. Beneficial mutation: A mutation that affects the organism in a good way. This type of mutation makes an organism more fit to survive.
Examples of the three types of mutations in bacteria. Neutral mutation:Deleterious mutation:Beneficial mutation: Color changeSilent mutationLoses ability to moveLoses ability to eat a certain foodCan't sense dangerCan't find foodCome up with your own:________________Moves fasterCan eat a new foodDetects dangerCan find foodCome up with your own:________________
So what happens to bacteria with each type of mutation?Let's make a prediction about what will happen in the scenario below: In the above picture there are four strains of bacteria, and four types of food. Each bacteria can eat some of the types of food. Let's see what happens when put the bacteria on the food. Make a prediction then click "next" to find out.
So what happens to bacteria with each type of mutation? Even though we started with the same number of each bacteria, the strain with the deleterious mutation can only grow on two of the foods so now there are fewer of that mutant (13% of the population). The strain with the beneficial mutation is now out-growing all the other strains (45% of the population).
So what happens to bacteria with each type of mutation? If we took these bacteria and gave them fresh food, the strain with the beneficial mutation would start with more bacteria and still grow better. It would grow to be about 75% of the population. The strain with the deleterious mutation would be out-grown by the more fit strain. In only a few generations almost all of the bacteria will carry the beneficial mutation, even the original strain could be over-taken by the more fit mutant. This is a very simple example, and reality is not this simple. However, it gives you an idea of how a simple mutation can lead to a species evolving into a stronger species. These little changes (mutations) to genes can easily spread if they help the organism survive.
About the site: I developed as a companion website to Everything a cell does is a direct result of the genetics of that cell, whether it is a single-cell organism or part of a much larger organism. Thus, understanding the cells requires an understanding of the basis of all of their behaviors. About the author: I am a microbiologist studying microbial pathogenesis and the host immune response. My studies have included work in many pathogens including Rabies and Influenza viruses, Mycobacterium tuberculosis, Francisella tularensis, and Salmonella enterica. I currently live just outside of Philadelphia, PA, where I work as a postdoctoral fellow researching antigen processing and presentation during rabies infection. My email is always open for suggestions, corrections, or any other comments. Please feel free to contact me: