Rest of Chapter 16 and Chapter 17. Homology Related organisms share DNA sequences inherited from a common ancestor

Rest of Chapter 16 and Chapter 17

Homology

Related organisms share DNA sequences inherited from a common ancestor.

Homology

Over time, the sequences in each species acquire independent mutations.

DNA sequences

All share the DNA and the genetic codeNo two species share the exact same DNA

sequence of nucleotidesMutations

Homology

The more time that has passed, the greater the number of sequence differences that will be present.

More information on DNA

Harmful mutations are selected against and eliminated

Neutral and advantageous mutations are preserved

Much of our DNA is noncodingCertain genes like cystic fibrosis

Human DNA is 99% identical to chimpanzee DNA – share common ancestor that lived 5-7 million years ago.

Human DNA is 40% identical to mouse

Homology

Closely related species will have fewer DNA sequence differences that species that are more distantly related.

Chapter 17Q & A: Evolution

Two main conclusions about life on Earth

• All living things are related• Different species have emerged over millions

of years• Usually due to genetic change

How old is the earth, and how do we know?

• Apollo II astronauts returned to earth with several lunar rocks from moon’s surface

• Rocks had clues to earliest history of our solar system

• Nebular hypothesis – collapse of the solar nebula formed the sun and the planets– http://setiathome.berkeley.edu/~korpela/astro10/html/lec6/sld033.htm – http://www.classzone.com/books/earth_science/terc/content/visualizations/es0401/es0401page01.

cfm

http://setiathome.berkeley.edu/~korpela/astro10/html/lec6/sld033.htm

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0401/es0401page01.cfm

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0401/es0401page01.cfm

How old is the Earth?

• Oldest rock was calculated to be some 4.4 to 4.5 billion years old

• Scientists estimate that the age of the earth―and of the solar system more generally ―is 4.54 billion years.

• Why was going to the moon so important in comparison to the information we can gather on Earth?

• What is the Acasta Gneiss???

Moon

• Moon’s surface has remained largely intact over the course of its existence.

• Earth is a swirling ball of molten lava that digests its rocky outer crust. Difficult to find undisturbed rock.

• Acasta Gneiss- Canada. Ancient rock about 4 billion years old


• Scientists use radiometric dating to determine the age of a rock. (geological clock)

• Radiometric dating uses radioactive isotopes―an unstable form of an element that decays into another element by emitting energetic particles (radiation)―as a measure for determining the age of a rock or fossil.– Uranium-238 and potassium-40


• When rocks form, the minerals in them contain a certain amount of radioactive isotopes. • http://www.youtube.com/watch?v=1920gi3swe4

• The radioactive isotopes decay by releasing high-energy particles from the nucleus, a change that causes one element to transform into another.

• The time it takes for half the isotope in a sample to break down is called its half-life.

http://www.youtube.com/watch?v=1920gi3swe4

http://www.youtube.com/watch?v=1920gi3swe4

Radioactive isotopes

• Different radioactive elements decay at different rates.

• Uranium-238 has a half-life of 4.5 billion years• Potassium-40 has a half-life of 1.3 billion years• Carbon-14 decays to nitrogen in 5, 730 years


• Because the isotopes decay at a known rate, they can be used to determine the age of the materials in which they’re found.

Rock

• Wind and water stripped off particles and carried them to other places– These can be compressed into new rock layers– This type of rock is called sedimentary rock (straitions,

layers of sandstone and limestone)– Grand Canyon in Arizona

• Most fossils are found in sedimentary rocks• Rock can also be formed from erupting volcanoes. Lava

cools and hardens to form igneous rock• Radiometic dating is performed on this type of rock

Sedimentary rocks cannot be dated by radiometic methods

Why????

When and how did life begin?

• At some point in the earth’s distant past, life did not exist. Then at later point, it did.

• Where did this life come from? How did it start?

• The precise details of the transition from nonliving to living are lost in the mists of time, but we can hypothesize how that transition might have occurred.


• Lots of theories of how life started?– Asteroid or meteorites?– Inorganic materials that combined complex

molecules• In 1953, University of Chicago chemist Harold

Urey and his graduate student Stanley Miller hypothesized that they could synthesize organic molecules by replicating the chemical environment of the early earth.


• To simulate the early environment, Urey and Miller combined hydrogen gas, methane, ammonia, and water vapor in a flask filled with warm water. They mimicked lightning by discharging sparks into the chamber.


• As the gases in the chamber condensed and rained into the water, a host of new molecules, including amino acids, was produced from these basic ingredients.

• This experiment showed that it was possible to create molecules of life from inorganic materials.


• Since Urey and Miller’s experiment, other researchers have confirmed and extended their results.– Amino acids, lipids, sugars, ATP

• Scientists hypothesize that, over millions of years, cells capable of reproducing formed.Lipids formed bubbles in water- ideas highly

speculative

What was life like millions of years ago?

• Humans were not around millions of years ago

• Much of what we know about life on earth comes from fossils.

• Based on fossil evidence and radiometric dating of rock layers from around the world, scientists have produced a geologic timescale of the earth.


• Earth has been around 4.6 billion years

• The geologic timeline shows that the earth’s geography and climate have gone through dramatic changes.

Life years ago

• First few million years or so earth was molten ball of lava continually bombarded by meteorites


• Precambrian Era• The oldest known fossils date from some 3.5

billion years ago. – Prokaryote fossil– Life only in ocean

• The atmosphere at this time lacked substantial oxygen, and the only organisms that could thrive were unicellular prokaryotes that used other gases as a fuel source.


• Still Pre-Cambrian Era• With the emergence and proliferation of

unicellular photosynthetic organisms between 3.0 to 2.5 billion years ago

• Oxygen began to accumulate in the atmosphere, opening the door for more complex eukaryotic organisms to evolve.– First eukaryotes


• The first multicellular eukaryotic organisms to make use of oxygen were green algae, which appeared 1.2 billion years ago.

• Precambrian


• Soft-bodied aquatic animals followed, about 600 million years ago, but it is only from 545 million years ago, during the Cambrian period, that we see fossil evidence of a truly diverse animal world.

• Cambrian Explosion during Paleozoic Era• Ocean life swelled mind-boggling array of strange –

looking creatures• Expansion of ocean animal diversity

• What is an Opabinia?


• The first organisms to colonize land were primitive plants, appearing roughly 450 million years ago.

• By 350 million years ago, forests of seedless plants covered the globe.

• Paleozoic Era


• A mass die-off known as the Permian extinction at the end of the Paleozoic Era that occurred 290 million years ago.

• An extinction is the elimination of all individuals in a species. Extinctions may occur over time or in a sudden mass die-off. In the Permian extinction, roughly 95% of living species were lost.


• The Permian extinction wasn’t bad for all organisms; some flourished as space and resources opened up for the survivors, who spread and diversified in a phenomenon known as adaptive radiation―the spreading and diversification of organisms

that occur when they colonize a new habitat.Reptiles who thrived in hot, dry climate – Triassic period


Mesozoic Era

Dinosaurs dominated the land for nearly 200 million years, until they died out in another mass extinction at the end of the Cretaceous period, 65 million years ago.

Reason for extinction is a mystery

Evidence suggests that a 6-mile-wide asteroid plowed into the earth and sent a thick layer of soot and ash into the atmosphere that blocked out the sun for months, leading to the extinction of the dinosaurs.


• With the extinction of the dinosaurs, mammals were able to spread and diversify on land and thus give rise to many of the species of organisms we see on the planet today.

• Cenozoic Era– Mammals, birds, flowering plants, etc. – Many large mammals go extinct


• This pattern of sudden change is seen in the fossil record and is an example of punctuated equilibrium―– the theory that change in most species occurs in

periodic bursts as a result of sudden environmental change.

Why are there no penguins at the north pole, and no polar bears at the south pole?• North pole and south pole have different

creatures but similar environment• Biogeography is the study of how organisms are

distributed in geographical space. • Biogeography seeks to explain why islands and

isolated land areas have evolved their own distinct flora and fauna.

• How did the Arctic (polar bears) and Antarctic (penguins) evolve their own distinct flora and fauna?

Penguins and Polar Bears

• Penguins live in southern hemisphere- coastal regions of Antarctica– Polar bears live in Arctic and evolve from brown

bears 150,000 years ago

• Why have they not migrated from one pole to the next???

• How did they get to their homes in the first place???

Why are there no penguins at the north pole, and no polar bears at the south pole?

Though today they are at opposite ends of the earth, the Arctic and Antarctic landmasses weren’t always so far apart.

250 million years ago the continents were bound together into one land mass- PangaeaRoaming was possible

Plate tectonics― the movement of the earth’s upper mantle and crust, which influences the geographical distribution of landmasses and organisms― formed the continents of the northern and southern hemispheres.

Great land masses split and split again - isolation

Are creatures that look alike always closely related?

• Species share a common ancestor. This is not the only reason that two species might appear similar

• Common ancestry is not the only reason that two species might appear similar. • Even species that are not closely related may

share similar adapations

Convergent Evolution

• Convergent evolution is the process by which organisms that are not closely related evolve similar adaptations as a result of independent episodes of natural selection.

• Cold-dwelling fish in Antarctic– Antifreeze protein that lowers body temperature– Arctic fish at the other pole have antifreeze

proteins– Genes that code for each protein are different

How many species are there on earth, and how do scientists keep track of them?

• Current estimates of the total number of species on earth range anywhere from 5 to 30 million, of which 1.8 million or so have been formally described.

How many species are there on earth, and how do scientists keep track of them?

• The process by which scientists systematically identify, name, and classify organisms on the basis of shared traits is called taxonomy.

Classification

• Kingdom---- Phylum---Class---Order---Family---Genus---Species

• Animals-----Chordata-----Mammalia-----Primates---Hominidae---Homo----Sapiens

• Vertebrates – rigid backbone• Humans are mammals

How many species are there on earth, and how do scientists keep track

of them?By studying the many similarities and differences

among organisms, taxonomists have come up with a system for sorting organisms into a series of eight progressively narrower categories:

Domain, kingdom, phylum, class, order, family, genus, and species.

As you move down the list, from domain to species, the categories get increasingly exclusiveFinally one member is includedGenus species names proved scientific name for every living

organism

Is a crocodile more closely related to a bird or to a lizard?

• Scientists represent phylogeny (the evolutionary history of a group of organisms) visually using a diagram called a phylogenetic tree.


• Phylogenetic trees contain a root, nodes, and branches.

Root – common ancestor shared by all organisms on the tree

Over time, different groups of organisms diverged from that common ancestor and from one another – leading to branches on tree

Points on the tree at which these branch points occur are called nodes

Node common ancestor shared by all organisms on the branch above the node

The most recently two groups share a common ancestor, the more closely that are related


• The more recently two groups share a common ancestor, the more closely they are related.

How many branches does the tree of life have?

• Since each living species sits on its own branch in a phylogenetic tree, the complete tree of life has as many branches as there are species in the world.

Phylogenetic trees

• Evidence in the trees comes from fossil records, physical traits, and shared DNA sequences. – For many years, it was just physical and behavioral

traits. More recently including DNA sequences.

• Tree of life has many branches– First living tree only included plants and animals.

Then added protists

• Now many branches to classify the diversity of life

How many branches does the tree of life have?

• Scientists group organisms into one of three large domains―Bacteria, Archaea, and Eukarya―which represent the three fundamental branch points in the trunk of the evolutionary tree.

• Archaea and Bacteria was the Kingdom Monera• Within the Domain Eukarya we now have four

kingdoms– Animalia, Plantae, Fungi, and Protista

Documents

Rest of Chapter 16 and Chapter 17. Homology Related organisms share DNA sequences inherited from a common ancestor