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Evidence for Evolution. Comparative Studies in Biochemistry DNA All living organisms possess the same four nitrogen base pairs (A, T, C, G) implies a common ancestor More closely related species would share a greater proportion of their genome
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Comparative Studies in Biochemistry DNA • All living organisms possess the same four nitrogen base pairs (A, T, C, G) implies a common ancestor • More closely related species would share a greater proportion of their genome • E.g chimpanzees share approx 98% of human genome (comparisons of ‘junk DNA’ reveal similar tends) E.g Endogenous retroviruses (ERV’s) • An RNA viral sequence that has become part of an organisms genome by a process of reverse transcription. (virus inserts itself into cells chromosome) • Make up approx 8% of human genome • Endogenous: will be inherited (virus must infect a chromosomes which will be inherited) • Offspring will therefore have a copy of the virus in the same place of the same chromosome in every cell. • Humans have 16 ERV’s which are also found in chimpanzees
Mitochondrial DNA (mtDNA) • mtDNA are circular molecules • Only inherited from mother • 5-10 per mitochondria, containing 37 genes (13 for cellular respiraction, other 24 for tRNA synthesis) • Animals have approx 500-1000 copies of mtDNA/cell • Human mtDNA consists of approx 16500 base pairs • Has a higher rate of mutation compared with nuclear DNA • mtDNA varies between individuals and represents the closeness of the organisms. • E.g. siblings are very similar • E.g if tracing back similarities in mtDNA a pedigree can be created
Protein Sequences • Comparing the type and sequence of amino acids in similar proteins from diff species • Ubiquitous proteins: proteins which appear to be present in all species which are responsible for tasks required for all life. (carry out same function regardless of species) • Similarities between ubiquitous proteins indicate close ancestry common ancestor E.gCytochrome C • Involved in cellular respiration • Human cytochrome C contains 104 amino acids. (37 of these amino acids have been found to be in the same position in all organisms) • Out of 104, the more which are similar the closer the species to each other. (e.g chimpanzees& gorillas are exactly the same as humans) • Table 16.3 e.g Alpha/Beta/Delta chains in haemoglobin - Alpha/Beta chains are identical in humans and chimps, gorillas differ by one amino acid - Delta chains differ by one in chimps and gorillas
Comparative Studies in Anatomy Embryology • Similarities between embryos of various species indicate a common ancestor (e.g. vertebrates) • E.g • embryonic gill pouches/arches • presence of a well developed tail, • Similar brain development, • two chambered heart
Homologous Structures - bones are arranged in a similar way despite their different function e.g forelimb of vertebrates
Vestigial Organs • structures of reduced size that appear to have no function • they are a waste of energy and resources and therefore natural selection caused their reduction in size • approx 90 in humans • E.g Humans • Nictitating membrane • Act as a transparent third eyelid in cats, birds, frogs etc but pinkish membrane in inner corner in each eye for humans • Muscle to move ears • Wisdom teeth • Cannot be used in mastication • Pyramididalis muscles (muscle above pubic bone) • Coccyx • Appendix • Body hair • Muscles contract around hair to trap a layer of air around body (insulation), but doesn’t work as human hair is too fine
Vestigial Organs • E.g. other vertebrates • Wings of flightless birds (ostriches/ emus) • Whales / snakes have pelvis/femur bones although both are non-functional
