Mutation The principal evolutionary mechanism in bacteria. For all organisms: the only source of new genetic information. Mutation: any heritable change.

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?