Other Evolutionary Mechanisms Genetic Equilibrium Vs Evolution In

Other Evolutionary Mechanisms

Genetic Equilibrium Vs. Evolution In genetic terms, evolution is any change in the relative frequency of alleles in a population. The situation when the allele frequencies remain the same is called genetic equilibrium. If the frequencies do not change, the population will not evolve.

Maintaining Genetic Equilibrium If there are no changes to DNA, and the allele frequency stays the same, the population is at genetic equilibrium which means no evolution has occurred. No C alleles allowed! This can be measured by looking at the Gene Pool of a population.

Maintaining a Species • In order to maintain a species (no new alleles in gene pool), certain criteria must be met. • There must be: – A large population – No change in DNA – No natural selection – No immigration or emigration – Random mating • These 5 conditions are referred to as the Hardy-Weinberg Principle.

• If the five Hardy Weinberg conditions are MET, then the population is in equilibrium (not changing) • If any ONE of them is affected, then the population will evolve

Population Size Effects In small populations, there are less options for mating, therefore any evolutionary changes occur more rapidly In large populations there are more alleles available, so one change does not make a big difference to the population These changes are due solely to chance factors. The smaller the population, the more susceptible it is to such random changes and loss in genetic variation.

If evolution DOES occur, it may be through: 1. Genetic drift – Bottleneck Effect – Founder Effect 2. 3. 4. Gene Flow Mutations Genetic Recombination

Genetic Drift is the random change in allele frequencies that occurs in small populations. Some individuals, just by chance, leave behind a few more descendents than others. This is different than natural selection because it is not survival of the fittest

Genetic Drift drift can cause populations to lose genetic variation and it does not usually create new adaptations. There are two types of genetic drift: – Bottleneck Effect – Founder Effect

The Bottleneck Effect Environmental events may reduce population sizes dramatically ex: earthquakes, floods, fires, and over hunting by humans Those that survive the disaster may not accurately represent the original population Alleles may be overrepresented among survivors, some may be eliminated completely.

The Founder Effect Occasionally a small group of individuals within a population may migrate and become isolated from the original population. This smaller group is the ‘founding’ population The result for this new founding population is often high frequencies of specific genetic traits inherited from the founding ancestor Certain alleles may go missing all together as a consequence, resulting in a loss of genetic diversity.

The Founder Effect The Mainland Population Island

The Founder Effect The Mainland A few individuals colonize a new isolated area

The Founder Effect There may be a higher frequency of one allele in the founder population just by chance This allele did not have been very common in the original population

The Founder Effect Island The island population grows

…after a few generations One allele may be lost completely if individuals fail to leave offspring carrying it. Island

…after a few generations Mutations may occur creating new alleles Island

…after a few more generations The new allele becomes more common Island

The 2 populations now look very different! The Mainland Island

The Fugates of Kentucky Stemming from one French immigrant, Martin Fugate, who moved to Kentucky in 1820, a gene for methemoglobinemia was introduced. The Fugates and their descendents suffer from a rare hereditary blood disorder where there is excessive methemoglobin in the blood. Because their circulating blood is less oxygenated, they appear various shades of blue, depending on how seriously they are affected.

Maria Concepcion Soto • • In the Lake Maracaibo region of northwest Venezuela, there is an extraordinarily high frequency of a disorder known as Huntington's disease. All of the Lake Maracaibo region Huntington's disease victims trace their ancestry to a woman named Maria Concepción Soto who moved into the area in the 19 th century. She had an unusually large number of descendants and was therefore the "founder" of what is now a population of about 20, 000 people with a high risk of having this unpleasant genetically inherited trait Approximately 150 people in the area during the 1990's had this rare fatal condition and many others were at high risk for developing it. NOTE: Huntington's disease is not unique to the Lake Maracaibo region. It occurs throughout the world at relatively low rates. About 200, 000 people in the United States (. 07% of the population) have it.

Amish Example of Founder Effect • Amish people of Lancaster County, Pennsylvania have a high incidence of Microcephaly. • From 1960 -2000, 61 babies were born (to 23 Amish families) that had this extremely rare fatal genetic disorder. • All of these families are descendants of a single Amish couple nine generations ago.

Remember…. If evolution DOES occur, it may be through: 1. Genetic drift – – 2. 3. 4. Bottleneck Effect Founder Effect Gene Flow Mutations Genetic Recombination

Gene Flow flow is when alleles are transferred from one population to another. This happens when there is migration. If alleles are carried to a population where those alleles previously did not exist, gene flow can be a very important source of genetic variation.

Gene Flow By moving alleles around, it can make distant populations genetically similar to one another, thus reducing the chance of speciation. Example: The allele for brown coloration moves from one population to another and eventually both populations will have brown alleles.

Remember…. If evolution DOES occur, it may be through: 1. Genetic drift – – 2. 3. 4. Bottleneck Effect Founder Effect Gene Flow Mutations Genetic Recombination

Mutations Mutations are random changes in DNA. Mutations can be beneficial, neutral, or harmful for an organism, but mutations do not “try” to supply what the organism “needs. ” To pass a mutation on to the next generation, it must occur to a reproductive cell (gamete).

Remember…. If evolution DOES occur, it may be through: 1. Genetic drift – – 2. 3. 4. Bottleneck Effect Founder Effect Gene Flow Mutations Genetic Recombination

Genetic Recombination Sexually reproducing organisms can create new combinations of alleles. Crossing-over that occurs in meiosis can recombine or “shuffle” alleles in sex cells.

Genetic Recombination When egg and sperm meet, the offspring inherits a combination of genes that is totally unique. Gametes carries versions of genes from previous generations plus any mutations that occurred during meiosis

Effect of Genetic Recombination Differences among individuals add to the diversity and variation within the population. Diversity means that alleles are changing over time, which means that evolution is occurring.

In Summary… Changes to a population over time = EVOLUTION No changes to a population = genetic equilibrium = NO EVOLUTION The four ways that changes CAN be made to a population are explained above!