CHAPTER 20: HUMAN EVOLUTION Understanding “Mitochondrial Eve” and the Out of Africa hypothesis

Learning goals To understand early human evolution. The “out of Africa” theory and the evidence that supports it. To understand how mitochondrial DNA analysis has provided evidence to support the “out of Africa” theory of human evolution. Required reading: Chapter 20: human evolution

Learning objectives Understand the differences between mitochondrial DNA and nuclear DNA. Understand how mitochondrial DNA is inherited Understand the methodology of mitochondrial DNA analysis and how it is used to trace ancestry. Discuss complementary ancestry-tracing methods (e.g. Y- chromosome analysis) Understand how data obtained from mitochondrial DNA analysis has provided support for the “out of Africa theory” of human evolution

Nuclear DNA vs Mitochondrial DNA Nuclear DNA undergoes homologous recombination Maternal and Paternal DNA are mixed Mitochondrial DNA does NOT undergo recombination Paternal chromosome Maternal chromosome Offspring inherit mixed chromosomes Circular Mitochondrial chromosome

Mothers pass mitochondrial DNA directly to offspring Sperm only contributes paternal DNA

Activity: “Mitochondrial Eve” and the inheritance of mtDNA

MtDNA can be used to trace human ancestry through maternal lines

Finding “Mitochondrial Eve” Wilson et al (1987) collected mtDNA samples from people all over the world How did they trace these DNA sequences back to a single origin?

Find the most likely ancestral sequence Imagine you found the following DNA sequences from mitochondria samples from several individuals. Can you reconstruct the likely ancestral sequence? AAGCCGTT AATCCCTA CATCGGTA AAGCCGTA AATCCCAA CATCCGTA AATCCGTA Think to yourself and then discuss with your neighbor

Through sequence analysis scientists can trace a mitochondria’s history AATCCGTA CATCCGT A AAGCCGTA AATCCCTA CATCGGTAAAGCCGT T AATCCCA A

Ancestry can be traced along paternal line using Y Chromosome analysis

Activity: Think-pair-share mitochondrial DNA has a high mutation rate relative to nuclear DNA. This quality of mitoDNA is important for tracing ancestry in a relative new species such as modern humans. Based on this information can you predict the relative amount of mutations in mitochondrial DNA from the following human populations? How can the amount of mutation in mitochondrial DNA be used to support the “out of Africa” theory? A. North America B. South America C. Africa D. Australia E. Europe F. Asia

Early humans originated from one geographical region