EK 1A2 Natural selection acts on phenotypic variations in populations

ENVIRONMENTS CHANGE AND ACT AS SELECTIVE MECHANISM ON POPULATIONS.  In polluted areas where soot built up on tree trunks (i.e. the Industrial Revolution), the dark-colored form of the peppered moth became more common. In unpolluted areas, light-colored forms remained predominant.  Experiments suggested that predation by birds was the cause; light-colored moths stand out on dark trunks, and vice versa.

 In the last 40 years, pollution has decreased in many areas (the Clean Air Act) and the frequency of light- colored moths has rebounded.  Recent research has questioned whether bird predation is the agent of selection. Regardless, the observation that the dark-colored form has increased during times of pollution and then declined as pollution abates indicates that natural selection has acted on moth coloration.

BLACK PEPPERED MOTH  djLc djLc  Ir9g Ir9g

ADAPTATION AND CAMOUFLAGE  nts.html nts.html

SOME PHENOTYPIC VARIATIONS SIGNIFICANTLY INCREASE OR DECREASE FITNESS OF THE ORGANISM AND THE POPULATION.  Sickle cell anemia and malaria  The best documented example of heterozygote advantage is sickle cell anemia which is a recessive allele. The heterozygous people for sickle cell anemia are much less susceptible to malaria. When the parasite that causes malaria is introduced into a person’s blood stream via mosquito bite enters a red blood cell, it causes extremely low oxygen tension and this causes the RBC to sickling of the cell.

 Such cells are quickly filtered out by the spleen, thus eliminating the parasite.  The reason the person with the homozygous recessive genotype for sickle cell gets the disease is because there are so many sickled cells, the spleen cannot filter all of them out.  ion.html ion.html

DEFINE ARTIFICIAL SELECTION AND DESCRIBE AN EXAMPLE  Artificial selection is when the breeder selects for the desired characteristics. An example is pure bred animals or plants