How do variations lead to adaptations

Paul Williams, switches hats for this program. As the developer of Wisconsin Fast Plants, he has firsthand experience observing variation and how it provides the raw material for change in populations over time. Robert Murray and Dr. Georgia Dunston , of the National Human Genome Center, introduce us to the role of genes as a source of variation. We hear of one example that applies to humans—PTC tasting—and we are presented later with a scenario in which the ability to taste PTC is an advantage that leads to change in a population.

The role of genes is emphasized as mutation is introduced as one cause of new variation in populations. As a contrast to natural selection, Dr. Williams describes how he developed Fast Plants through artificial selection. And Bottle Biology returns as Dr. Williams features a bottle system for studying the fundamentals of evolution. What distinguishes living things from dead and nonliving things? No single characteristic is enough to define what is meant by "life.

How can we make sense of the living world? During this session, a systematic approach to biological classification is introduced as a starting point for understanding the nature of the remarkable diversity of life on Earth. One characteristic of all life forms is a life cycle — from reproduction in one generation to reproduction in the next.

This session introduces life cycles by focusing on continuity of life in the Animal Kingdom. In addition to considering what aspects of life cycles can be observed directly, the underlying role of DNA as the hereditary material is explored. What is a plant? Tibetans thrive at altitudes where oxygen levels are up to 40 percent lower than at sea level. Most people can survive at high altitudes for a short time because their bodies raise their levels of hemoglobin, a protein that transports oxygen in the blood.

However, continuously high levels of hemoglobin are dangerous, so increased hemoglobin levels are not a good solution to high-altitude survival in the long term. Tibetans seemed to have evolved genetic mutations that allow them to use oxygen far more efficently without the need for extra hemoglobin.

Organisms can also exhibit behavioral adaptation. One example of behavioral adaptation is how emperor penguins in Antarctica crowd together to share their warmth in the middle of winter. Scientists who studied adaptation prior to the development of evolutionary theory included Georges Louis Leclerc Comte de Buffon.

He was a French mathematician who believed that organisms changed over time by adapting to the environments of their geographical locations. Another French thinker, Jean Baptiste Lamarck, proposed that animals could adapt, pass on their adaptations to their offspring, and therefore evolve. The example he gave stated the ancestors of giraffes might have adapted to a shortage of food from short trees by stretching their necks to reach higher branches. Lamarck theorized that behaviors aquired in a giraffe's lifetime would affect its offspring.

Natural selection, then, provides a more compelling mechanism for adaptation and evolution than Lamarck's theories. An adaptation is passed from generation to generation. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

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They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource. Also, many genetic changes have no impact on the function of a gene or protein and are not helpful or harmful.

In addition, the environment in which a population of organisms lives is integral to the selection of traits. Some differences introduced by variants may help an organism survive in one setting but not in another—for example, resistance to a certain bacteria is only advantageous if that bacteria is found in a particular location and harms those who live there. So why do some harmful traits, like genetic diseases, persist in populations instead of being removed by natural selection? There are several possible explanations, but in many cases, the answer is not clear.

For some conditions, such as the neurological condition Huntington disease , signs and symptoms occur later in life, typically after a person has children, so the gene variant can be passed on despite being harmful. For other harmful traits, a phenomenon called reduced penetrance , in which some individuals with a disease-associated variant do not show signs and symptoms of the condition, can also allow harmful genetic variations to be passed to future generations.

For some conditions, having one altered copy of a gene in each cell is advantageous, while having two altered copies causes disease. The best-studied example of this phenomenon is sickle cell disease : Having two altered copies of the HBB gene in each cell results in the disease, but having only one copy provides some resistance to malaria.

This disease resistance helps explain why the variants that cause sickle cell disease are still found in many populations, especially in areas where malaria is prevalent.

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