Mutation
The principal evolutionary mechanism in bacteria.
For all organisms: the only source of new genetic information.
Mutation: any heritable change in the structure or amount of genetic material.
Different levels of mutation
DNA: mistakes made during DNA replication
Spontaneous (random)
Only mutations occurring during meiosis can affect the next generation.
Effects of a mutationDepends on how it affects the functioning of the protein.
Is a mutation harmful or beneficial?Determined by the environment.
Hemoglobin: 2 alpha chains, 2 beta chains
Gene for the alpha chain in chromosome 16Gene for the beta chain in chromosome 11
Natural Selection in Humans: Alternative hemoglobins and malaria
Hemoglobin A considered normalHbA/HbA
Hemoglobin S is an alternative formHbS/HbS
Phenotype: Sickle-cell anemia—destruction of red blood cells.fatal without medical intervention.
HbA/HbS
Phenotype: Sickle cell traitDebilitating only in situations of low oxygen availability
Frequency of HbS allele Frequency of malaria
Estimated malarial cases: 2006-2008: 243,000,000Estimated malarial deaths: 2006-2008: 863,000
Base substitution
Hemoglobinmolecules stackwhen O2 is lowCells deform
Beta-chain Affected
146 aa
6th aafrom end ofbeta chain
• Heterozygotic individuals (HbA/HbS ) do not experience sickle cell anemia.
• The environment of the rbc with HbA/HbS is not conducive to survival of the malaria parasite.
• Without medical intervention, natural selection operates against two groups:– 1. HbA/HbA: individuals die from malaria.– 2. HbS/HbS: individuals die from sickle cell anemia.– HbA/HbS is favored, therefore can the HbS allele be
eliminated?