Pearson - The Biology Place
Question: How do we use the Hardy-Weinberg model to predict genotype and allele frequencies? What does the model tell us about the genetic structure of a. Understanding the deep connection between allele frequency and evolution can Genetics: A Fundamental Relationship Between Genotype Frequencies and. In technical terms, this is known as allele frequency. The genotype of a specific organism consists of a set of genetic instructions for building.
This mathematical abstraction allows key questions in evolutionary genetics to be addressed. This population genetic state is represented by a point in genotype frequency space, where each dimension corresponds to the frequency of a particular genotype. As genotype frequencies change over time, evolving populations explore genotype frequency space Rice However, not every possibility can be realized.
Populations are constrained to a restricted set of genotype frequencies. Trivially, genotype frequencies must sum to one. Mendelian segregation and patterns of mating further restrict the set of possible genotype frequencies.
For example, in a randomly mating population it is unlikely that every individual will be the same heterozygous genotype. Natural selection also influences patterns of genetic variation, as high-fitness genotypes are found at higher frequencies than neutral expectations. Today, evolution is typically defined as a change in the genetic makeup of a population over generations—a definition that encompasses both the large-scale evolution Darwin envisioned and the smaller-scale processes we'll discuss in this article.
Natural selection is the mechanism that Darwin proposed to explain how evolution takes place and why organisms are typically adapted, well-suited, to their environments and roles. The basic idea of natural selection is that organisms with heritable traits that help them survive and reproduce—in a certain environment—will leave more offspring than organisms without those traits.
Allele frequency & the gene pool
Because the traits are heritable, they will be passed on to the offspring, who will also have a survival and reproduction advantage. Over generations, differential survival and reproduction will lead to a progressive increase in the frequency of the helpful traits in the population, making the population as a group better-suited to its environment. Natural selection is not the only mechanism of evolution. Populations can also change in their genetic composition due to random events, migration, and other factors.
However, natural selection is the one mechanism of evolution that consistently produces adaptation, a close fit between a group of organisms and its environment.
Darwin did not, however, know how traits were inherited. But the algae that drift lower don't have much yellow light--the water absorbs the yellow and lets more bluish light through so the deeper algae need red protein to do well at greater depths.
If you were to sample the algae at the surface, the healthiest ones would be green, while the healthiest algae under the surface would be red. But the algae all breed with each other, so the percentage of green-protein and red-protein genes would be pretty stable from generation to generation.
The stability of the allele frequency is described by the Hardy-Weinberg principle. Change Now imagine there is a year of heavy storms.
The algae in the pond overflow the banks and spread to neighboring ponds. One of the neighboring ponds is very shallow, and the other is much deeper. In the shallow pond, the red-protein gene is not helpful, so more pure green-protein algae are successful.
That will tend to drive the red-protein gene out of the gene pool--that is, it will reduce the allele frequency of the red-protein gene. The opposite may happen in the deep pond. In deep waters, the green-protein is of no help.