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Paper Topic:

biology

p 3 BIOLOGY 1 . Stands of aspen trees often are a series of genetically identical individuals , with each succeeding tree growing from the severed shoot of another tree . Using what you`ve learned of genetics in this chapter would you expect one aspen tree in a stand to differ greatly from another in its phenotype ? Would you expect each to look exactly like the next in terms of phenotype ? Evaluate It is expected that each aspen tree would look exactly like the next in terms of phenotype . This form of plant propagation through

an asexual method has been used in particular plant species to preserve specific traits that are either desirable or helpful . These traits may include resistance to diseases and insects , flower or leaf color and flavor Positioning a stand of an aspen tree onto a severed shoot of another tree is a form of grafting which is generally used in breeding a variety of shrub or tree . The twig or scion of an aspen tree is inserted into a nick that is situated on the stump of another aspen tree which serves as the stock . The principle behind this is to connect the cambiums of the scion and the stock so that there will be a continuous transmission of water and other nutrients from the roots of the stock to the growing twig . It is expected that the phenotype of the grafted twig will be identical to the twig 's source . In the genetic level , the twig contains its specific genetic constitution in its DNA Hence , the twig is programmed to grow into the expected phenotypic features of its source , regardless of transferring to a stock tree by grafting . The stock tree only serves as a source of water and nutrients that could provide nourishment to the twig at a faster rate , thus making the grafted twig develop at an earlier time without affecting the original phenotypic features because the genotype of the twig has already been established at an earlier time during its development Some plant scientists employ the grafting technique in determining what environmental factors can affect the phenotype of a grafted twig . It has been established that the phenotype of a grafted twig is the product of the genotype as it is influenced by its environment . 2 . The text notes that an alternate allele of the hemoglobin gene can cause sickle-cell anemia when a person is homozygous for this allele but that a person who is heterozygous for the allele actually can derive a benefit from it--protection from malaria . In the United States , 8 percent of African Americans are carriers for the sickle-cell allele while in central Africa the figure is 20 percent . What could account for this difference ? Assess Sickle-cell disease originated from at least four sites in Africa and in the Mediterranean region . Knowing this fact , sickle-cell anemia is thus present in all countries of Africa and in all the rest of the areas around the globe where Africans must have migrated to . In...

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