Other Methods of Evolution Other Methods of Evolution - Artificial Selection | Gene Flow | Genetic Drift Other Methods of Evolution Artificial Selection | Gene Flow | Genetic Drift

Other Methods of Evolution Learning Objectives Describe the process of artificial selection Explain how gene flow, and genetic drift can change a gene pool  After this lesson you will be able to describe the process of artificial selection. You should also be able to explain how gene flow, and genetic drift can change a gene pool.

Non-Random Mating (artificial selection) Natural selection – the process by which organisms with favorable variations survive and produce more offspring than less well–adapted organisms Non-random mating– the selective breeding of organisms in order to increase the frequency of favorable traits Produces changes in gene pool due to direct involvement of humans Has been used for many years In natural selection, the gene pool of a population changes over time based on a culmination of natural and random events. Artificial selection, also known as selective breeding, produces changes in a gene pool due to the direct involvement of humans. In artificial selection, humans choose to breed organisms that have desirable traits in the hopes of magnifying those traits in future generations. Artificial selection has been used for many years.

Non-Random Mating (artificial selection) Gregor Mendel used non-random mating in experiments with pea plants Selects organisms with alleles for desired traits Plant with fast growth allele bred with plant with large fruit allele Some offspring would have both favorable traits Hybridization – the breeding of different varieties of organisms Gregor Mendel used artificial selection in his experiments with pea plants. The process of artificial selection begins by selecting organisms that have the allele for the desired traits. For example, a plant that has the allele for fast growth could be bred with a plant that has the allele for large fruit. At least some of the offspring would have both favorable traits. Further breeding would ensure that the favorable traits become mainstream in the plant population. This process of breeding organisms of different varieties is called hybridization.

Artificial Selection Human use Drawbacks Dog breeding Agriculture Growing crops Raising cattle Drawbacks Lowers genetic diversity of population Some traits may be lost from population Population more susceptible to change Disease puts entire population at risk Humans have used artificial selection in a variety of ways. Dog breeding has resulted in many different types of dogs that now look and behave very differently from the wolf from which they evolved. Artificial selection is also used in agriculture, from growing crops of plump tomatoes to raising cattle with lean muscle. There are some drawbacks to artificial selection. The process of artificial selection lowers the genetic diversity of a population. Some traits not being selected for may be completely lost from the population. Lower genetic diversity also makes the population more susceptible to change. For example, if a disease enters the population, the entire population is at risk. In the wild, a similar disease would place just a portion of the population at risk because of genetic variation.

Artificial Selection Examples in agriculture Cows selected for milk production Livestock selected for size Creation of new varieties of food Artificial selection is used extensively in agriculture. Cows are artificially selected for milk production. Livestock, such as cows, pigs, and chickens, are artificially selected for size. A large pig will provide more food than a small pig. Artificial selection is used in crops to select for strong, disease-resistant plants that produce large amounts of food. Artificial selection is also used to create new varieties of food. The wild mustard plant was selected for a variety of different traits in order to produce broccoli, cabbage, kale, cauliflower, Brussels sprouts, and kohlrabi. For example, large leaves were artificially selected for in order to create kale. Selection for terminal buds resulted in cabbage, while selection for lateral buds resulted in Brussels sprouts. Artificial selection of the wild mustard plant has resulted in a variety of new crops.

Gene Flow Gene flow – the transfer of alleles from one population to another Results Introduces new alleles into populations Increases variation in gene pool Variation fuels natural selection and evolution Examples Migration Seed transfer Gene flow is the transfer of alleles from one population to another. This often happens because of migration, when organisms from one population move to another population. Gene flow can also occur from seed transfer. Imagine two plant populations, the first having a unique allele. If an animal carries a seed containing this unique allele to the second plant population and it begins to grow, the second population has gained this allele. Gene flow introduces new alleles into populations, thereby increasing variation in a gene pool. In turn, the variation fuels natural selection and evolution.

Genetic Drift Genetic drift – the process by which changes in allele frequencies occur as a result of random events Random events cause allele frequencies to fluctuate unpredictably Affects small populations the most Allele frequency dependent on total alleles in population Genetic drift is the process by which changes in allele frequencies occur because of random events. Consider flipping a coin. There are equal chances of getting heads or tails, but that does not mean that half of the flips will be heads and half will be tails. Random chance allows the results to differ from theoretical probability. The same holds true for allele frequencies in populations. Random events cause allele frequencies to fluctuate unpredictably from one generation to the next. Genetic drift affects small populations the most because allele frequency is dependent on the total alleles present in a population.

Genetic Drift Situations that increase effect of genetic drift Bottleneck effect – a genetic drift as a result of an environmental change that reduces the original population to one that has a drastically different gene pool Chance determined which allele frequencies survive There are two situations that increase the effect of genetic drift. A drastic change in environment, such as a natural disaster, may significantly reduce the size of a population. The surviving population may have a gene pool that is much different from the starting population. This is referred to as the bottleneck effect. A bottle is filled with blue, red, and yellow marbles. If the bottle is turned upside down, only a few marbles come out at a time because of the narrow size of the bottle’s neck. The marbles that do come out are selected by chance. Whereas the starting population included blue, red, and yellow marbles, the new population includes a majority of blue marbles and only one yellow marble. The red marble variation disappeared entirely. This is analogous to the limited population that survives a drastic environmental change, such as a fire. Instead of selection pressures allowing organisms with certain traits to reproduce more, chance determined which organisms (and therefore allele frequencies) survive.

Genetic Drift Situations that increase effect of genetic drift Isolated population composed of random individuals Founder effect – a genetic drift as a result of a portion of a population becoming isolated and having a drastically different gene pool from the original population Some alleles overrepresented Some alleles not present The other situation that may increase genetic drift involves allopatric speciation. In allopatric speciation, part of a population is geographically isolated from the parent population. The isolated population will be composed of individuals chosen at random from the parent population. This creates the founder effect, in which the allele frequencies present in the new population may be drastically different from those in the parent population. Some alleles may be overrepresented, while others may not be present at all.

Other Methods of Evolution Learning Objectives Describe the process of artificial selection Explain how gene flow, and genetic drift can change a gene pool  You should now be able to describe the process of artificial selection. You should also be able to explain how gene flow, and genetic drift can change a gene pool.