Electronic Theses and Dissertations

Identifier

387

Date

2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biology

Committee Chair

Tit-Yee Wong

Committee Member

Charles Williams

Committee Member

Carlos Estrano

Committee Member

Donald D Ourth

Abstract

The mitochondrial Cistronic Stop Signal Ratios (CSSR) is defined as a series of 12 numerals representing the ratio of TAA, TAG, AGG, and AGA nucleotide trimmers. Primate mitochondria use these nucleotide trimmers as stop codons and many of these trimmers are also found on the 2nd and 3rd reading frames of a cistron. We showed that the average value of the CSSR of all the 13 protein coding genes in mitochondria (genomic CSSR) could be used to define the phylogenetic relationship between the primates. However, the genic CSSR of most human mitochondria are essentially identical, except for the CSSR of the ND5 gene. Attempts were made to see if the CSSR profiles of the human mitochondrial ND5 gene could be used to shade some light on the evolution of humans. The hierarchical correlation of the CSSR of 315 hominoid ND5 genes was analyzed. Using the CSSR of gorilla ND5 as out-group, and assuming the human-gorilla split about 7 million years before the present (yr BP), a phylogenic tree of the ND5 gene was constructed. Result suggested that human ND5 gene began to change about 600,000 yr BP. Present day humans can be classified into 5 major branches with a total of 35 different CSSR clades. Members belonging to the same clade are often concentrated at certain geographical locations of the world. However, these clades also have their members scattered in various parts of Africa. The CSSR value of the Neanderthals ND5 gene is closely correlated to one of the major branch of the ND5 genes. The rate of ND5 gene diversification was diphasic. The CSSR of ND5 gene diversified logarithmically till 170,000 yr BP. The rate of ND5 gene diversification accelerated after 130,000 yr BP. Such acceleration rate of ND5 gene diversification cannot be explained by the 'molecular clock' theory. However, horizontal gene transfer, possibly through interbreeding with other hominoids, could explain the increase in diversification of the ND5 gene in humans. The timeline of human ND5 gene evolution generated by CSSR analysis generally agrees with most of the archaeological and molecular data of human evolution. We also suggested the early humans migrated in and out of Africa frequently. This explains the diversity of CSSR profiles in the African continent. Our independent assessment and our results would resolve many inconsistencies in human anthropology.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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