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In recent years, ancient DNA has been used to understand aspects of Neanderthal biology. Both mitochondrial (mtDNA) and nuclear DNA have been extracted from fossils and sequenced. These sequences have provided information about the appearance, speech capability and population structure of Neanderthals as well as their phylogenetic relationship with anatomically modern humans.
Neanderthal DNA bears on several debates concerning the origins of modern humans. What was the relationship between Neanderthals and anatomically modern Homo sapiens? Did Neanderthals and anatomically modern humans interbreed? Did Neanderthals contribute to the modern genome? How much? Scientists answer these questions by comparing Neanderthal DNA and mtDNA to that of modern humans.
DNA consists of phosphates, sugars and bases arranged in a chain. There are four different bases: adenine, thymine, guanine and cytosine. DNA is wound together in a double stranded molecule with adenine paired with thymine and cytosine paired with guanine across the two sides of the strand. When DNA is replicated, the chemical bonds that bind together the two sides are broken and new nucleotides are joined to the unwound strand, generating strands with the same sequences as the original. Mutations arise when an error in the copying occurs and a different base is substituted.
Different combinations of bases code for different amino acids, which are the building blocks of proteins. Sometimes more than one combination of bases leads to the same amino acid. For example, both AAA and AAG code for lysine. Therefore, a DNA change that led to a G at the third position rather than an A wouldn’t affect the code for lysine. This is known as a silent change. However, if the third position had changed to a C, making the set AAC, that would change the amino acid to asparagine. This change that could affect the protein is called nonsynonymous.