CLASS NOTES: The Molecular Clock (Human Evolution: Past and Future)

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Notes on video lecture:

The Molecular Clock

Human Evolution: Past and Future

John Hawks, University of Wisconsin

Notes taken by Edward Tanguay on February 10, 2014 (go to class or lectures)

Choose from these words to fill the blanks below:

function, gorillas, fossil, cladogram, homenoids, GULOP, Bailey, species, Sivapithecus, macaques, hemoglobin, Pauling, phylogeny, assumption, amino, 17, globin, genetically

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phylogeny [figh-LAH-jin-nee]

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understanding of the relationship between

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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

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macaques

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not a part of the group that includes the other homenoids

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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 of the groups

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humans are most similar to chimpanzees

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humans and chimps are next most genetically similar to

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we're more distantly related in genetics to

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1962 Linus and student Emil Zuckerkandl

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researched which 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 amino acids different

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proposed the theory "the molecular clock"

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differences in amino acids in 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

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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 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. 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-

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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 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 record

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e.g. [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

Vocabulary:

pseudogene, n. a non-working gene, or gene that once worked in ancient organisms but stopped working at some point in our evolutionary history, e.g. psi-eta-globin which still exists in the DNA of all primates but not longer produces a product ⇒ "In the discussions of genetic diseases in humans, pseudogene mediated gene conversion that introduce pathogenic mutations into functional genes is a well known mechanism of mutation."

phylogenetics, n. The study of evolutionary relationships among groups of organisms, which are discovered through molecular sequencing data and morphological data matrices. Evolution is a process whereby populations are altered over time and may split into separate branches, hybridize together, or terminate by extinction. The evolutionary branching process may be depicted as a phylogenetic tree, and the place of each of the various organisms on the tree is based on a hypothesis about the sequence in which evolutionary branching events occurred. ⇒ "Molecular phylogenetics is the branch of phylogeny that analyses hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships."

macaque, n. [mah-KAK] aside from humans (genus Homo), the macaques (genus Macaca) are the most widespread primate genus, ranging from Japan to Afghanistan and, in the case of the barbary macaque, to North Africa ⇒ "One study of crab-eating macaques found that a female has a greater likelihood to engage in sexual activity with a male if he had recently groomed her, compared to males who had not groomed her."

clade, n. group consisting of an ancestor and all its descendants, a single branch on ancestrial tree, many familiar groups, rodents and insects for example, are clades; others, like lizards and monkeys, are not (lizards excludes snakes, monkeys excludes apes and humans) ⇒ "The term "clade" was introduced in 1958 by Julian Huxley after having been coined by Lucien Cuénot in 1940."

cladogram, n. [CLAY-doh-gram] a diagram used in cladistics which shows relations among organisms ⇒ "A cladogram showing the terminology used to describe different patterns of ancestral and derived character states."

cladistics, n. an approach to biological classification in which organisms are grouped together based on whether or not they have one or more shared unique characteristics that come from the group's last common ancestor and are not present in more distant ancestors ⇒ "A sister group or sister taxon is a systematic term from cladistics denoting the closest relatives of a group in a phylogenetic tree."

People:

Linus Pauling (1901-1994)

American biochemist who received the 1954 Nobel Prize in Chemistry and the 1962 Nobel Peace Prize

one of the most influential chemists in history and ranks among the most important scientists of the 20th century
one of the founders of the fields of quantum chemistry and molecular biology
1926: awarded Guggenheim Fellowship to study under German physicist Arnold Sommerfeld in Munich, Danish physicist Niels Bohr in Copenhagen and Austrian physicist Erwin Schrödinger in Zürich, all three were experts in the new field of quantum mechanics