Genetic variations within and between populations

[Tosh5457]

This paper asserts these two different conclusions:

Thus the answer to the question “How often is a pair of individuals from one population genetically more dissimilar than two individuals chosen from two different populations?” depends on the number of polymorphisms used to define that dissimilarity and the populations being compared. The answer, can be read from Figure 2. Given 10 loci, three distinct populations, and the full spectrum of polymorphisms (Figure 2E), the answer is 0.3, or nearly one-third of the time. With 100 loci, the answer is ∼20% of the time and even using 1000 loci, 10%. However, if genetic similarity is measured over many thousands of loci, the answer becomes “never” when individuals are sampled from geographically separated populations.

The fact that, given enough genetic data, individuals can be correctly assigned to their populations of origin is compatible with the observation that most human genetic variation is found within populations, not between them.

How don't they contradict each other? What exactly is "variation between populations" and "variation within populations"?

 

[Ygggdrasil]

There are likely a small number of sites that differ between populations that can be reliably used to distinguish those populations. However, there are a larger number of sites that differ within a population.

 

[Tosh5457]

There are likely a small number of sites that differ between populations that can be reliably used to distinguish those populations. However, there are a larger number of sites that differ within a population.

I don't understand, can you explain it in another way?

 

[aroc91]

I don't understand, can you explain it in another way?

Overall variation may be too high to distinguish populations from each other, but that doesn't mean there can't be specific genes that are still unique to their respective populations.

 

[LudusRex]

I can provide an explanation for the apparent contradiction in the two conclusions presented in this paper. The concept of genetic variation within and between populations is a complex one and requires a thorough understanding of population genetics.

Firstly, it is important to understand that genetic variation refers to the differences in DNA sequences among individuals within a population. These variations can be caused by mutations, genetic recombination, and natural selection. On the other hand, genetic variation between populations refers to the differences in gene frequencies among different populations.

The paper presents two different conclusions because they are looking at genetic variation from two different perspectives. The first conclusion, which states that individuals from different populations can be genetically more dissimilar than two individuals from the same population, is based on a smaller number of loci (specific regions of DNA) being used to define genetic dissimilarity. In this case, it is possible to find significant genetic differences between individuals from different populations due to the limited number of loci being analyzed.

However, as the number of loci used increases, the second conclusion becomes more relevant. This conclusion states that when individuals are sampled from geographically separated populations and a large number of loci are analyzed, the genetic differences between these populations become negligible. This is because the majority of genetic variation is found within populations, rather than between them. In other words, the genetic differences between populations are relatively small compared to the genetic differences within populations.

To understand this concept better, imagine a large jar filled with different colored marbles. Each marble represents a different individual within a population, and the different colors represent genetic variations. If we randomly select two marbles from the jar, the chances of them being different colors (representing genetic differences) are quite high. However, if we increase the number of marbles in the jar and continue to randomly select two, the chances of them being the same color (representing genetic similarities) also increase.

In summary, the two conclusions presented in the paper do not contradict each other. They simply highlight the importance of considering the number of loci being analyzed and the populations being compared when studying genetic variation. It is essential to use a large number of loci and consider the genetic variations within and between populations to get a complete understanding of human genetic diversity.