The example of the sickle-cell allele demonstrates a key aspect of evolution through natural selection, in that
A. adaptation and fitness are in relation to the individual organism, not the general population.
B. human populations in the tropics are the most susceptible to random changes caused by natural selection.
C. natural selection increases the variety in a population upon which subsequent natural selective processes can act.
D. adaptation and fitness are in relation to specific environments; traits are not universally adaptive or maladaptive.
E. although natural selection usually acts upon the phenotype, it can sometimes act upon the genotype.
Question 2
Which of the following statements about the HbS allele is NOT true?
A. It is found in higher gene frequencies in regions where malaria is endemic.
B. It causes sickle-cell anemia in homozygous individuals.
C. In areas where malaria has been reduced through drainage and insecticides, its frequency declines.
D. Heterozygous individuals have an increased immunity to malaria.
E. Homozygous individuals usually develop fatal cases of dysentery.
Antineoplastic agents and the cell cycle
A Gaze-Direction Cell
Surface molecules involved in the interaction between an antigen-presenting cell and a CD4+ T cell.
Normal white blood cell and a white blood cell undergoing apoptosis
Gametes from trihybrid organisms with different allele configurations
Genetic therapy for mice with sickle cell disease