Population Genetics

Population genetics is the statistical study of the natural differences found within a group of the same organisms. Instead of examining the genes of individuals, it looks at the dominant (the trait that first appears or is visibly expressed in the organism) and recessive (the trait that is present at the gene level but is masked and does not show itself in the organism) genes found within an entire population. Population genetics seeks to understand the factors that control which genes are expressed. It also creates mathematical models to try to predict which differences will be expressed and with what frequency.

In the life sciences, a population consists of all the individuals of the same species (all of the same kinds of organisms, like all the tigers) that live in a particular habitat at the same time. Scientists know that in any population, whether it be tigers or people, the individuals that make it up are all different. They may all be tigers, but each has individual and very recognizable traits.

Although some might think that all animals of the same species look exactly alike, it is known that once someone becomes familiar with a certain group of the same species, he or she can usually tell one from another. At first all black labrador retrievers look alike. After a closer look, it can be seen that there are very obvious and easily recognizable differences among them. It is known that it is mostly the individual's genetic inheritance that accounts for these minor differences. This means that the unique combination of dominant and recessive genes that the individual has inherited is responsible for all of its individual traits (color, size, abilities, and tendencies, to name only a few).

WHAT IS POPULATION GENETICS?

Population genetics is a tool used to study the genetic basis of evolution (the process by which gradual genetic change occurs over time to a group of living things), and it is helpful in allowing scientists to understand the relative importance of the many factors that influence evolution. It studies a given population's gene pool (which is the total of all of the genes available to a generation). Knowing what the gene pool consists of enables scientists to establish a sort of genetic base out of which future offspring will be composed. This assumes that over time, the population is made up of individuals that breed only with others of their species that live in the same habitat.

HARDY-WEINBERG LAW

Once the gene pool is established, scientists are able to use Mendel's laws of inheritance (concerning patterns of dominant and recessive genes) and predict what differences there will be among individuals in that population. Scientists are able to establish what are called gene frequencies, or percentages at which certain genes will be expressed. Scientists also have been able to establish a law that actually measures what changes will take place. Called the Hardy-Weinberg law, since it was proposed independently in 1906 by the English mathematician Godfrey H. Hardy (1877–1947), and the German physician Wilhelm Weinberg (1862–1937), this is a mathematical formula that has become the basis of population genetics. Using this formula (which only works perfectly when certain ideal conditions are met), scientists are able to describe a steady state called genetic equilibrium. In this state, gene frequencies stay the same and nothing changes unless some outside force intervenes.

Naturally, the real world, especially that involving human beings, is not perfect and there are many factors always at work that make conditions less than ideal. Chance events happen all the time. Reproduction does not always work and individuals leave populations while others may wander in. These are only a few potential variables. However, the Hardy-Weinberg formula is still useful and helps in being able to arrive at some relative frequencies, so it is still applies in some way to the real world.

WHY STUDY POPLUATION GENETICS?

By studying what makes individuals in the same population different, science is able to learn more about evolutionary change. Population genetics can also draw very useful conclusions. For example, when populations of interbreeding individuals are very small, they are highly susceptible to extinction by any number of chance events. This is because their interbreeding has not given them much genetic variation (differences). When something in their habitat changes, they may be unable to adapt quickly enough. Population genetics, therefore, is a valuable, if not always statistically perfect, tool for life scientists.

[See alsoDominant and Recessive Traits; Evolution; Genetics; Population ]