How does microevolution work

When a small number of parents produce just a few offspring, allele frequencies in the offspring may differ, just by chance, from allele frequencies in the parents. This is like tossing a coin. If you toss a coin just a few times, you may, by chance, get more or less than the expected 50 percent heads and 50 percent tails. Due to such chance variations in small populations, allele frequencies drift over time.

There are two special conditions under which genetic drift occurs. They are called the bottleneck effect and founder effect. Mutation creates new genetic variation in a gene pool.

It is how all new alleles first arise. In sexually reproducing species, the mutations that matter for evolution are those that occur in gametes. Only these mutations can be passed to offspring. For any given gene, the chance of a mutation occurring in a given gamete is very low. Thus, mutations alone do not have much effect on allele frequencies.

However, mutations provide the genetic variation needed for other forces of evolution to act. Gene flow occurs when individuals move into or out of a population. If the rate of migration is high, this can have a significant effect on allele frequencies. Allele frequencies may change in the population the migrants leave as well as in the population the migrants enter.

An example of gene flow occurred during the Vietnam War in the s and s. Many young American servicemen had children with Vietnamese women. Most of the servicemen returned to the United States after the war.

However, they left copies of their genes behind in their offspring. In this way, they changed the allele frequencies in the Vietnamese gene pool. Do you think the gene pool of the U. Why or why not? Natural selection occurs when there are differences in fitness among members of a population. As a result, some individuals pass more genes to the next generation than do other members of the population. This causes allele frequencies to change over time. The example of sickle cell anemia, which is shown in the following table and described below, shows how natural selection can keep even a harmful allele in a gene pool.

The allele S for sickle cell anemia is a harmful, autosomal recessive allele. It is caused by a mutation in the normal allele A for hemoglobin the oxygen-carrying protein on red blood cells. Malaria is a deadly tropical disease that is common in many African populations.

Heterozygotes AS with the sickle cell allele are resistant to malaria. Therefore, they are more likely to survive and reproduce. This keeps the S allele in the gene pool. Microevolution is defined as changes in the frequency of a gene in a population. These are subtle changes that can occur in very short periods of time, and may not be visible to a casual observer.

Mathematically, we can determine whether microevolution is occuring by assessing whether a population is in Hardy-Weinberg Equilibrium. The five "forces" that can cause shifts in gene frequency microevolution are:. Detecting microevolutionary change. Subscribe to our newsletter. Email Facebook Twitter. Or you can go back to the Evolution cover page. Possible consequences of genes of major effect: transient changes in the G-matrix. Genetica 33— Google Scholar. Antonovics, J. Turner, Heavy metal tolerance in plants.

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