Microevolution over time leads to speciation or the appearance of novel structure, sometimes classified as macroevolution. One in every 3,000 babies is born with NF1, and this holds true for all populations worldwide (Riccardi 1992). A mutation occurs in one of the cells that changes the texture of the cell membrane from a relatively smooth surface to a highly ruffled one. The smooth cells were well-adapted to ingesting tiny bacteria but poorly suited to encapsulating the larger bacteria. The situation changed, however, as the Industrial Revolution took off. The fact is, though, that every genetic adaptation that has helped our ancestors survive since the dawn of life is directly due to a beneficial mutationa changes in the DNA that provided some sort of advantage to a given population at a particular moment in time. Its also possible that the mutability of the NF1 gene confers certain advantages to humans as well. This occurred approximately 66 million years ago. Genetic drift can This causes episodes of extreme pain and can cause serious problems in the oxygen-deprived tissues. This helped to camouflage the moths as they rested on a tree, making it harder for moth-eating birds to find and snack on them. Returning again to the example of our primordial cell population, lets imagine that, after the volcanic fissure opened up in the ocean floor, wiping out the majority of the parent population, two surviving populations developed in the waters on opposite sides of the fissure. The devastating effects of sickle cell anemia made its high frequency a pressing mystery. Approximately half of these cases are due to spontaneous mutationsthat is, the person is the first in their family to have the disorder. Negative frequency-dependent selection serves to increase the populations genetic variance by selecting for rare phenotypes, whereas positive frequency-dependent selection usually decreases genetic variance by selecting for common phenotypes. In the United States, its estimated that 72,000 people live with the disease, with one in approximately 1,200 Hispanic-American babies and one in every 500 African-American babies inheriting the condition (World Health Organization 1996). WebYou should recall the major evolutionary forces that can alter population gene pools include: 1. mutations 2. emigration/immigration (gene flow) 3. random genetic drift 4. natural selection Let us now consider each of these evolutionary agents as it applies to population genetics. Another example involves the introduction of the Harlequin ladybeetle, Harmonia axyridis, native to East Asia, to other parts of the world as a natural form of pest control. While some populations are fairly stable, others experience more flux. He saw how insome of the populations one of the alleles went extinct, arising from nothing generationnumber 0 2 generationnumber 20 vialnumber 107 Even strains specifically developed to be flightless (to curtail the. In addition to natural selection, there are other evolutionary forces that could be in play: genetic drift, gene flow, mutation, nonrandom mating, and environmental variances. Genetic drift is the unpredictable fluctuation in allele frequencies from one generation to the next because of a population's finite size 1.
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