The population in South Africa is more prone to sickle cell anemia (genotype "ss"). People with genotype "ss" survive only up to
14-15 years of age. People with "SS" are prone to malaria because the parasite resides inside their RBCs. People with genotype "Ss" are resistant to malaria because the parasite cannot reside inside their RBCs, and they can live a normal life (without sickle cell anemia).What kind of evolutionary force must be operative in South Africa?
<span>Sickle-cell anemia is a recessive disorder caused by the presence of two recessive alleles "s", so genotype is "ss". This disorder is characterized by sickle hemoglobin. In an area with malaria, heterozygous individuals "Ss" (with one dominant allele and one recessive allele) have an advantage. These individuals will have both normal and sickle hemoglobin. But pathogen that causes malaria affect only normal hemoglobin, so heterozygous individuals will have half of the hemoglobin resistant to the pathogen and those individuals are resistant to malaria.</span>
Stabilizing selection favors heterozygotes Ss, disruptive selection favors dominant (SS) and recessive (ss) homozygotes, while directional selection favors dominant (SS) or recessive (ss) homozygote. Since in this example, people with genotype Ss (heterozygotes) are in advantage, then this is an example of stabilizing selection.
a point mutation only mutates and changes that particular spot in the DNA strand while a frameshift changes the whole strand by moving the bases either one forward or backward
Explanation: Receptors. Receptors are groups of specialised cells. They detect a change in the environment stimulus. In the nervous system this leads to an electrical impulse being made in response to the stimulus.
