by Susanne Kassube
* Note: to read Genorme (part1) click here.
Planet earth is currently home to seven billion people [1]. In comparison, the approximately 60,000 orangutans remaining in the wild represent an exceedingly small number [2, 3]. Despite this 140,000-fold difference in current population size, analysis of the orangutan genome yields a surprising discovery: orangutans are much more genetically diverse than humans. If you compare the genome sequences of two randomly chosen orangutans, you will find twice as many differences than if you compare the genome sequences of two randomly chosen humans [4]. Even within orangutans, diversity is higher among the smaller Sumatran population, which consists of less than 7,000* individuals than it is among humans! The striking differences in orangutan genome sequence diversity provide important clues about primate evolutionary history.
*The most recent survey, however, indicates 14,000 individuals.
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Figure: DNA
Each DNA molecule consists of two strands that form a double helix. The specific order of the four letters A, G, C and T in each strand encodes the information contained in the genetic material.
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Genetic information is stored in the form of DNA. The alphabet of the genetic code consists of the four letters A, G, C, and T, which are abbreviations for the chemical names adenine, guanine, cytosine, and thymine. The specific order of the four letters encodes the genetic information and serves as a template for the production of the molecules that are required to build every single cell in the body and to keep it functioning. Every time a cell divides, its DNA is copied so that each new daughter cell receives a complete set of instructions on how to build the molecules of the cell. In a similar way, instructions are passed on from parents to their offspring, and DNA is accordingly known as "hereditary material". Since DNA is passed down from generation to generation, it provides a record of our evolutionary history. New DNA sequencing techniques have enabled us to sequence whole genomes (the entire genetic sequence of an organism) and facilitate their detailed analysis. Comparisons of DNA sequences between species and within individuals of the same species have, in recent years, provided surprising new insights into the evolutionary history of the great ape family that had previously been difficult to obtain via other methods.
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Figure: SNPs
A single nucleotide polymorphism or SNP is the change of a single letter in the genome. While the first individual maintains the original T, the second individual carries a C at the same location in its genome. In the human genome, SNPs occur on average at every 300th letter. In the orangutan genome, SNPs occur twice as frequently, as they are found at every 149th letter.
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