Agents of Change

In a nutshell, everything not operating under Hardy-Weinberg.

• Natural selection is the increase or decrease in allele frequency due to its survival benefit for the organism. Natural selection is discussed thoroughly in the next section.
  
  
• Mutations are random changes in an organisms genetic code that may lead to the formation of a new allele. Most mutations, however, are harmful.
  
  
• Gene flow is the addition or reduction of alleles when individuals enter and leave the population.
  
  
• Genetic drift is the random increase or decrease of the occurrence of an allele in a population. Genetic drift is the most evident in small populations. The founder effect is a type of genetic drift that occurs when the organisms in the founding group have different allele frequencies from the population they left. The resulting offspring will reflect the genetic makeup of the founders. A population bottleneck is another type of genetic drift that occurs when the population undergoes a dramatic decrease in size. This may lead to the removal of some alleles from the gene pool if all the carriers of that allele were wiped out.
  
  
• Nonrandom mating occurs when individuals choose mates based on certain traits. Sexual selection is when females choose males based on their appearance or their competence in some other area. Nonrandom mating also occurs when individuals choose mates from only nearby individuals. Inbreeding is when individuals mate with relatives.