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 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 copies of mtDNA/cell Human mtDNA consists of approx 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.g Cytochrome 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 o 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 o Cannot be used in mastication -Pyramididalis muscles (muscle above pubic bone) -Coccyx -Appendix -Body hair o 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