This gradual favoring of advantageous traits within a population is called natural selection, and it directly affects the population's gene pool. A gene pool is the collection of alleles found in all the individuals of a population.

A normal distribution shows an arrangement of data in which most of the values fall in the middle of the data set, represented by the mean. The curve that results is bell-shaped and symmetrical. The frequency is highest near the mean value and decreases toward each extreme end of the range. This means that for a population showing normal distribution, the alleles for the mean phenotype are more advantageous than the alleles associated with either extreme phenotype.

When organisms move between populations and bring their genes with them, that's gene flow! This helps increase genetic diversity!

Sometimes changes in gene frequencies happen by chance - that's genetic drift. In small populations, these random changes can have a big effect on which traits become common or rare.

The northern elephant seal suffered from the bottleneck effect. This is genetic drift resulting from an event that drastically reduces the size of a population. Through genetic drift, some alleles can be completely lost from the gene pool and others can be fixed in the population, resulting in lower genetic diversity.

Ever wonder why peacocks have those amazing tail feathers? That's sexual selection at work. When animals choose mates based on certain traits, those traits become more common in the population.

Allele frequency can also be expressed as a percentage by multiplying the frequency by 100. The frequencies of all the different alleles in a population should equal 1.0, or 100 percent.

Allele frequency is used to track genetic variation in populations and detect changes in alleles. Imagine that periodic fires blacken the ground in the habitat shown in the Field Mice Alleles diagram. The black mice may be better camouflaged, providing more protection against predators. If they survive and reproduce more effectively than brown mice, the frequency of the b allele may increase over time relative to the B allele frequency.