Question

Which piece of evidence does not support the theory of recent (ca. 200,000 years ago) African origin of humans?
a. Mitochondrial DNA sequences coalesce to Africa populations about 125,000 years ago. b. Linkage disequilibrium of nuclear genes gets progressively lower as one measures populations farther from Africa. c. Haplotype diversity of nuclear genes is greatest in Africa d. Fossils of modern humans older than 60,000 years are found only in Africa. e. Non-African populations show reduced heterozygosity compared to African populations.

Answer 1

Correct Answer is:

b. Linkage disequilibrium of nuclear genes gets progressively lower as one measures populations farther from Africa.

There is obvious genetic differentiation among human populations, but levels of population structure are generally low. In an analysis of the same Human Genome Diversity Project (HGDP) dataset, it was found that the among-population component represents only 9% of total human genetic diversity. Population structure is more pronounced for genetic variation in the mitochondrial genome. Because of its asexual and effectively haploid mode of inheritance, the mitochondrial genome has a lower effective population size and, therefore, should experience higher rates of genetic divergence between populations as a result of drift . Accordingly, large geographical regions such as Europe and East Asia are highly enriched for a small fraction of mitochondrial haplotype diversity, reflecting the history of repeated bottlenecks as human populations migrated out of Africa. The geographically structured distribution of mitochondrial genetic variation may also have been shaped by local adaptation to environmental conditions such as climate. Therefore, the significant but generally weak statistical associations between nuclear and mitochondrial polymorphisms that are prevalent throughout the human genome are consistent with our understanding of human population genetics and demographic history.