THINGS YOU SHOULD KNOW:
In “La Ciència al Teu Món” you can find the explanations, proposals, and the educational materials needed to learn about many different genetic and biological concepts in-depth. For now, we will highlight the most important concepts you’ll need to cover to order to make proper use of the analysis modules.
DNA, Genes and Genomes: DNA is the molecule that contains all the information needed for an organism to develop and function. Genes are segments of DNA, and all of these segments together on all the chromosomes, form the organism’s genome.
Mutations: A mutation is a change in the sequence or structure of the DNA. Mutations occur randomly, and any position in the genome can change or mutate – from the most important position to the most insignificant one.
Transposable Elements (TEs): Transposable Elements (or mobile elements) are capable of inducing mutations. They are DNA fragments with the ability to jump around the genome, changing their position (also known as transposition). Sometimes, while jumping, they can create copies of themselves.
Types of Mutation According to Their Effect. Mutations can affect individuals when:
- They have a negative or deleterious effect. A mutation can modify or disrupt the function of a nearby gene, which could lead to negative consequences for the individual, such as an illness.
- They are neutral. This occurs when a mutation has no effect on the function, structure or control of a gene; or any other control or regulation system in the genome.
- They have a beneficial or adaptive effect. A mutation might allow the individual to better adapt to the environment, allowing it to survive and reproduce.
Sadly, mutations do not introduce themselves to us by saying: “Hello, I am an adaptive mutation!” Instead, distinguishing and classifying mutations into one of three categories, (deleterious, neutral or adaptive), is one of the big problems facing scientists studying TEs.
Natural Selection and Mutation Frequency: Natural selection, one of the basic mechanisms of evolution, is a process that acts upon all populations. Just like mutation, natural selection is inevitable.
Due to natural selection, deleterious mutations either disappear rapidly (in evolutionary terms, of course) from a population, or remain only in a few individuals, keeping them at low frequencies.
Let’s take an extreme example. Let’s imagine a deleterious mutation that results in an individual becoming sterile and unable to produce any descendants. What happens to the mutation in the following generation? It won’t be passed on because the sterile individual will not produce another generation to carry that mutation. This results in the mutation being effectively eliminated by natural selection.
On the other hand, if a mutation is neutral, it will have no effect on the probability of an individual producing offspring. Whether or not an individual in the next generation carries the mutation is up to chance. Random forces tend to shape the population frequency of these kinds of mutations.
Finally, if a mutation is adaptive, it will likely be found at a very high frequency in a population. For example, if a mutation alters a fly’s wing beat in such a way that it becomes irresistible during mating, then this mutation will increase mating success, which should result in an increase the number of descendants; therefore, increasing the number of individuals carrying this mutation. These decedents will then, in turn, pass it on to their own descendants. In a short time, (in evolutionary terms, remember), most of the individuals in this population will go on to carry the cool wing beat gene. We should find this adaptive mutation at a high frequency in this fly population.
The way we estimate the frequency of a specific mutation is by counting how many individuals in a population have it in their genome.
Recombination:
Recombination is a natural process that occurs during cell division, where homologous chromosomes swap DNA fragments. Sometimes, recombination fails, and this exchange takes place amongst two similar rather than homologous sequences, such as two TEs. In general, these kinds of mistakes are not just deleterious to cells, but also for the TE sequences, which can be deleted in the process. This kind of improper recombination is most likely to occur in regions of high recombination frequency, and this results in TE sequences being deleted more frequently than they would in low recombination regions. Moreover, in low recombination regions, TEs can more easily copy and paste themselves throughout the genome, as the cellular mechanisms used to control mistakes are less strict in these areas.
Drosophila melanogaster: the main character
The fruit fly (Drosophila melanogaster) is one of the favorite model organisms of genetic researchers. You can learn a lot about this “research star” on the CSIC webpage: https://www.seresmodelicos.csic.es/mosca.html.
When studying the evolutionary genomics of Drosophila, it is very important to know a bit about its history. Fruit flies, along with humans, originally came from Africa – specifically modern-day Zambia. Nearly 16,000 years ago, this fly spread from the African continent and colonized the rest of the world. This is known as the “Out-of-Africa” event. During those 16,000 years, flies that were used to the tropical conditions of Africa had to adapt to the cold and arid conditions found in Europe.
1.2. TEST YOURSELF
Answer the following questions to test whether or not you are prepared for the next module. (You can try as many times as you wish):
