Coalescent Theory Explained


Coalescent theory is a model of gene divergence distribution within genealogy. It is used to estimate population genetic parameters. This may include migration rates, population size, or recombination rates within a natural population. It is done by tracking a specific sample backwards from the current moment to a place in history where the two lineages of that sample coalesce.

The coalescent theory will then estimate the expectation of this time period and the variances that may be encountered during the process. This allows researchers to determine if there is a probability that there is a sharing of parental DNA.

What Are the Applications of Coalescent Theory?

One of the most useful applications of coalescent theory is to use it for disease gene mapping. Although this process is still being developed, by researching lineage and DNA strands, it becomes possible determine how genetic malformations began and the conditions that may have contributed to their development. This information can then lead us toward more effective treatment options because we understand the diseased gene’s presence more completely.

It also allows us to strengthen the breeds of plants and animals more effectively. We can focus on specific genetic traits that we want while eliminating traits that we do not want. Horse breeding is a classic example of this. If there is a horse with a specific coat pattern or gait that is wished to be duplicated, then that horse will bear some offspring that will have these traits and some that will not. The offspring with those traits will be allowed to breed and the offspring that does not will not be allowed to breed. Over the course of several generations, the traits will be passed along genetically more often than not.

It can also be used to document regional variations in heterozygosity. Heterozygosity occurs when there are two different alleles of a gene contained within the cells at a gene locus. Coalescent theory allows us to explain variations that are found based on genetic models and sequences. Chromosomes tend to cluster in accordance to certain power and distribution laws, allowing us to recognize and then explain recombination events when they occur.

What Does Coalescent Theory Mean for Species Evolution?

In most theories of evolution, the process is some variation of the “survival of the fittest.” Changes that create variation within a species are naturally replicated in the same ways that we approach modern horse breeding. Nature naturally selects the best traits and then replicates them when those traits give a species a certain advantage.

Coalescent theory supports a different point of view, which is referred to a “neutral evolution.” In the neutral theory of evolution, changes at the molecular level occur because of genetic drift. Mutant alleles can cause changes that are either positive or negative and those genetic traits will continue to persist within a species, whether they are beneficial or not. Then the theories of natural selection take place after the neutral evolution occurs, eliminating the mutations that may be negative so that the species still has the opportunity to survive.

Assumptions Made by the Coalescent Theory

In order for the coalescent theory to work, there are a few assumptions that must be made. The largest assumption is an elimination of changes to the alleles that may occur through chance events. The theory must assume that there is no random genetic flow or drift that occurs out of or into population centers.

It must also assume that natural selection is not currently working within the given population and that alleles are not recombining to form newer or more complex alleles.

Then, if all of these assumptions can be held as truth, a common ancestor can be found for two distinct species. Using the example of horse breeding, most modern horse breeds can be traced back to the Arabian breed, even though today they are two distinct breeds with very different conformation standards.

Coalescent theory takes this comparison to a different level. It could be used to determine the common ancestor between chimpanzees and humans, for example, or a common ancestor between trees and grass.

As we learn more about genetics and how information passes along from generation to generation, we will be able to make the calculations in the coalescent theory become more accurate. This will produce better simulations of ancestry that can help us understand more about who we are because we know where we came from in the past.

Think about it like this: maybe we all have a little stardust in our genes.