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phylogeny [figh-LAH-jin-nee]

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understanding of the relationship between species

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the relationship between species is a fundamental aspect of how evolution happened

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when we add genetics to phylogeny, it gets complicated and involves math

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how we use phylogeny to understand when certain species shared common ancestors with each other

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humans, chimpanzees, gorillas, orangutans

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four species of living homenoids

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macaques

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not a part of the group that includes the other homenoids

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cladogram shows clades, or branches of an ancestral tree

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today we use cladograms to understand the study of biology

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allows you to understand the relationships between organism

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genetics

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genetics by and large reflect the phylogeny of the groups

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humans are most genetically similar to chimpanzees

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humans and chimps are next most genetically similar to gorillas

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we're more distantly related in genetics to macaques

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1962 Linus Pauling and student Emil Zuckerkandl

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researched which amino acids there were in a protein hemoglobin in different kinds of organisms

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seemed to show that the number of differences in the amino acid sequences seemed to reflect the time that those organisms shared a common ancestor according to the fossil record

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e.g. humans and apes are 1 amino acid different, yet humans and horses are 17 amino acids different

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proposed the theory "the molecular clock"

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differences in amino acids in hemoglobin are accumulating at a regular rate over time

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if this were true, we could determine how long two species shared a common ancestor as a separate way than using the fossil record

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i.e. we could look at how different they are and determine that they shared a common ancestor beginning at a certain time in the past

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1992: research, Wendy Bailey

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studying a part of the DNA called the psi-eta-globin

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a part of the genome which is near the betaglobin gene which is part of hemoglobin

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in some ancient organisms psi-eta-globin may have been functional but in all living primates, it has lost its function, it doesn't make any product anymore

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why would something that has no function exist and persist in primate genomes?

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our genomes are full of genes that once worked in ancient organisms but stopped working at some point in our evolutionary history

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some primates share a deactivation of the gene that creates vitamin C, some animals have no problem creating vitamin C, but primates have to get vitamin C from external sources

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e.g. GULOP which still exists in the human genome

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the further we move away from humans into other primates, the higher the difference of the gene sequence for psi-eta-globin

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the percentage differences between the genes allows us to put age estimates on when the branchings occurred

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e.g. humans and macaques in terms of their DNA are about twice as different than humans and orangatans are

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this is what is referred to as the molecular clock

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molecular clock is an assumption that genes change at a constant rate but there may be mutations which cause them to converge on each other

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to estimate times from these percentages, you have to know how often genetic changes happen, to further increase accuracy, you have to root this to the fossil record

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e.g. Sivapithecus [shee-vah-PITH-i-kuss] is a genus of extinct primates that may have been the ancestor to modern orangutans, fossil record indicates that it lived about 12 million years ago