Natural Selection in Human Populations

• Natural Selection and Disease• The CCR5 gene• Gene is transcribed and translated to a surface

protein of T-helper cells. • Related to HIV (human immunodeficiency virus• Virus acquired from chimpanzees ca. 1930• Does no harm in chimpanzees.• Related to AIDS (acquired immune deficiency

syndrome)

Prevalence of HIV infection, ages 15-45

Increase over time in HIV prevalence in adults

Life cycle of HIV

Azidothymidine (AZT)treatment

Fast acquisition of resistance toAZT

• Some people are resistance to HIV

• CCR5 – delta 32 allele

• Sickle cell anemia and malaria

• Global incidence of malaria: 300-500 cases/year

• 1-3 million deaths/year

• Hemoglobin

• HbA HbS

• HbA/HbS = heterozygote advantage

HbA/HbS

sickle cell trait

HbS/HbS

sickle cell anemia

Frequency of HbS

Prevalence ofmalaria

Relationship between HbS and malarial impact