SIMULATION OF NATURAL SELECTION
Plastic or paper bag containing 100 beads of two colours additional beads as needed. AIM
To prove that both allele and genotype frequencies in a population would not remain constant if natural selection occurs. Natural selection is the process whereby organisms better adapted to their environment tend to survive and produce more offspring. INTRODUCTION
Natural selection, the differential survival and reproduction of individuals was first proposed by Darwin as the mechanism of for evolution. Although other factors have since been found to be involved in evolution, selection is still considered an important mechanism. Natural selection is based on the observation that individuals with certain heritable traits are more likely to survive and reproduce than those lacking those advantageous traits. Thus, the population of those organisms with these advantageous traits will increase in the next generation. In this experiment we are considering the sickle-cell disease which is caused by a mutant allele (Hb-) which in the homozygous condition in the past was often fatal to people at quite young ages. The mutation causes the formation of abnormal, sickle-shaped red blood cells that clog vessels, cause organ damage, and are inefficient transporters of oxygen. Individuals who are heterozygous (Hb-Hb+) have the sickle-cell trait (a mild form of the disease), which is not fatal. Scientists were surprised to find a high frequency of the Hb- allele in populations in Africa until they determined that heterozygous individuals have a selective advantage in resisting malaria. Although the homozygous condition may be lethal, the heterozygotes are under both a positive and a negative selection force. In malaria countries in tropical Africa, the heterozygotes are at an advantage compared to either homozygote. HYPOTHESIS
The hypothesis here states that both allele and genotype frequencies in a population remain constant as far as a few...
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