Cytochrome-c is a protein and is a gene product. It functions as a key enzyme in oxidation reactions and seems to occur in practically every living organism. There are 20 different amino acids. Cytochrome-c consists of a chain of 112 amino acids, 19 of which occur in exactly the same sequential order positions in all organisms tested. Differences in the identity and positions of the remaining 93 amino acids are considered to be the result of mutational substitution during the course of evolution. The amino-acid constitution of human cytochrome-c differs from that of many but not all other species. There are no differences in the cytochrome-c taken from humans and from chimpanzees, and only one difference between human cytochrome-c (the amino acid isoleucine in position 66) and that from the Rhesus monkey (threonine in that position). The numbers of differences in the cytochrome-c of various species compared with that of humans are: cow, pig and sheep (10), horse (12), hen and turkey (13), rattlesnake (14), dogfish (23), fly (25), wheat (35), yeast (44), etc.1 Information of this nature is used to construct phylogenetic trees of assumed genetic relationship. This is presented as evidence for evolution on a molecular level and, among other things, it is concluded that man and the chimpanzee have a relatively recent common ancestor
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