Molecular Markers for Phylogenetic Studies and Germplasm Conservation

Molecular Markers for Phylogenetic Studies and Germplasm Conservation

DOI: 10.4018/978-1-7998-4312-2.ch005
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Abstract

Application of molecular markers in phylogenetic studies has become increasingly important in recent times. Availability of fast DNA sequencing techniques and robust statistical analysis methods provided new momentum to this field. Different nuclear encoded genes (16S rRNA, 5S rRNA, 28S rRNA), mitochondrial encoded genes (cytochrome oxidase, mitochondrial 12S, cytochrome b, control region), and few chloroplast encoded genes (rbcL, matK, rpi16) have been used as molecular markers. This method allows researchers to obtain new evidence concerning their phylogeny and biodiversity. Measurement of genetic diversity is important for development of strategies for effective germplasm management. The DNA-based technologies can overcome all the limitations of traditional methods used for the estimation of genetic diversity. This chapter deals with historical developments of molecular phylogeny, use of molecular markers in phylogeny, and evolution of phylogenetic tree building methods.
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Phylogenetics And Molecular Cloak

Studies on amino acid sequence of hemoglobin in different animal species by Zuckerkandl and Pauling (1965) has provided remarkable information. They observed that hemoglobin molecule of human and mouse differ by only 16 amino acids, between human and horse by 18 amino acids, between horse and mouse by 22 amino acids, while between human and shark by 79 amino acids. These observations imply that there has been a constant rate of substitution of amino acids over time. To explain this phenomenon, Zuckerkandl and Pauling (1965) proposed the molecular clock hypothesis. According to the hypothesis, the difference in amino acids between different organisms correlates with the evolutionary time scale. The difference in amino acids between mammals are less compared to that between the mammals and fish (shark). Apparently, a biomolecule has been acting like a molecular clock. Greater will be the distance between two organisms, if the differ by more number of amino acids and vice versa. Thus the distance between them can be estimated in the evolutionary timescale. Using this hypothesis it has been estimated that humans and apes diverged about five million years ago. However, validity of the hypothesis has been questioned as changes in biomolecules can occur at different rates.

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