Weighing the Evidence

Today we will try to assess whether humans and chimpanzees share a

common ancestor

NEW CORE CURRICULUM: FOUNDATIONS OF THE SCIENTIFIC PROCESS

hypothesis: humans and chimpanzees share

a common ancestorOne of the core propositions of biological evolution is that organisms alive today can be traced back through time to a common ancestor. Evolutionary biologists assert that the more similar organisms are genetically, the more closely related they are, and the more likely they

are to have evolved from a recent common ancestor. In this activity, you will be considering whether the data you review supports the hypothesis that humans and chimpanzees share a

common ancestor.

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hypothesis: humans and chimpanzees share

a common ancestorYou will review each data set with your team members.

After you review each data set, consider with your team members whether you think that data set supports the hypothesis. Then record in the chart how confident you are that the hypothesis is true based on the evidence.

With each new data set you review, record your confidence level based on all the evidence you have reviewed to that point.

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We will break up into discussion

groups of 5 students

Have the weighing the evidence worksheet out the whole time.

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Data Set 1Physical traits in common between Chimps and

Humans

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Data Set 1: Comparing Pan & Homo

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SkullsThe lower jaw of a chimpanzee juts out from its face whereas, the profile of a human tends to be more vertical

TeethAll non-human hominids, have canines which can serve as weapons. The teeth are also arranged in a U-shape, whereas human jaws are more parabolic

BrainHuman brains are much larger, do most of their growing after birth and areas of the cortex involved in learning are greatly expanded.

Mystery of theMatching

Marks

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DO I HAVE YOUR ATTENTION?For some reason, a GUNSHOT seems to suggest a CRIME SCENE…

with BULLETS…

and BULLET RIFLING MARKS…

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As everyone knows from CSI BULLET RIFLING MARKS are used to solve crimes.

HOW?

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RIGHT!They are used to COMPARE

bullets found at a crime scene,

with bullets that werefired from suspect guns

Here are the marks from a crime scene

bullet…

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and here are the marks from bullets fired from four possible suspect

guns…

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A B

C D

Which bullet matches

the crime scene bullet?

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A

Crime Scene:

Which bullet matches the crime scene bullet?

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B

Crime Scene:

Which bullet matches the crime scene bullet?

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C

Crime Scene:

Which bullet matches the crime scene bullet?

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D

Crime Scene:

RIGHT! It’s a bullet shot from gun C.

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C

Crime Scene:

So what does that tell us?

YOU’VE GOT IT! The Crime Scene bullet and bullet C came from the

SAME GUN !

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C

Crime Scene:

We could say the bullets had a “Common Origin”

Many studies have told us that when any two items

with COMPLEX PATTERNS MATCH EACH OTHER

perfectly, we can be confident

that they had a…

COMMON ORIGIN !

KEEP THIS IN MIND:When we find other

COMPLEX PATTERNS that MATCH,What does this tell us?

They had a…“COMMON ORIGIN”

This is our theme:Matching Complex Patterns =

COMMON ORIGIN

What is this?

Right, it’s a HUMAN KARYOTYPE

A Human Karyotype has photos of all the matched pairs of human

chromosomes from one cell, stained to show banding patterns,

and arranged from long to short, with centromeres near the top.

Here are our numbers 6-9…

On the next slide, you will see another kind of human

karyotype:It has diagrams of

the chromosomes, with only one member of each

pair, clearly showing their banding patterns…

And on the next slide, you will see a similar

diagrammatic karyotype,

but this is from a NON-HUMAN

SPECIES…

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NEXT, we wll see both karyotypes together,

showing the matching chromosomes side by side:

each human chromosome is on the left…

each NON-human chromosome is on the right

As you COMPARE the CHROMOSOMES,side-by-side,

what is MOST surprising?

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What is most surprising?

Did you notice how very SIMILAR they are? Here’s a closer look at the first

seven:

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Any identical ones? What did we say about items with IDENTICAL COMPLEX PATTERNS?

RIGHT!Identical Patterns = COMMON

ORIGIN

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How would this applyto two different SPECIES

with IDENTICAL banding patternson their CHROMOSOMES?

RIGHT!They MUST have a Common Origin, or

a COMMON ANCESTOR !

Time for a Revelation…

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The clear chromosome evidence

of identical banding patterns

tells us that humans andchimpanzees must have had

a…

The non-human species is

the CHIMPANZEE

COMMON ANCESTOR !

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Somewhere, in our distant past,there was an ape-like species

thatgave rise to two lines of

ancestry.One branch led to modern

CHIMPS, the other branch led to HUMANS.DNA analysis and fossils tell us

thatthis split was around

6-7 million years ago (6-7 mya)

<---Common Ancestor

Chimps Us

6 mya

NOW

As a groupDiscuss

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Data Set 2: Comparing Chromosomes

That’s pretty strong stuff...

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And seems to conflict with Traditional Views!

Is there any other evidence that supports this conclusion?

Let’s take another look at thosechromosomes… [next set of slides]

Part 2

Data Set 3: The Chromosome Shuffle

Chromosomes contain all of our genetic code.Humans have 23 pairs of chromosomes that exist in nearly every cell in the body.

As part of natural genetic changes over time, chromosomes are rearranged in a number of different ways, including:inversions, deletions,

translocations, fission, fusion.

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CHROMOSOME PARTSAll Chromosomes have

telomeres at both ends(like shoelace aglets!)

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HeadTelomere

Centromere

TailTelomere

ttagggttagggttagggttagggttagggttaggg…||||||||||||||||||||||||||||||||||||aatcccaatcccaatcccaatcccaatcccaatccc…

Telomeres have a special DNA sequence…

Data Set 3: The Chromosome Shuffle

As a group work on the handout

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Data Set 4: Human Chromosome 2

We’ll do this one together

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Let’s look at our two sets of chromosomes again, side-by-

side.

This time, Focus on their DIFFERENCES:What do you see in the

chimp chromosomes (on the right) that is DIFFERENT from

the human chromosomes (on the left)?

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How are they different?

GOOD EYES!- Chimp’s #2 is shorter than our #2

-Chimp has an extra unmatched chromosome

What could have happenedto cause those differences?

Let’s take a closer look at those chromosomes…

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ANY IDEAS that might EXPLAIN the

“missing” part of the chimp’s #2 chromosome,AND the chimp’s “extra”

chromosome?

“Missing” part “Extra” in chimps

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Maybe the chimp’s“extra” chromosomewas once part of its

short #2.

Could the “extra”chromosome match the upper part of

our #2?

LET’S TRY IT…

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Nope!They don’t seem

to match.What else could

we try?

Turn the “extra” oneupside down?!

Let’s try it…

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WOW !IT WORKED! They DO MATCH!

NOW, the next question:“How could this happen?”

- Was there ONE #2 in ourcommon ancestor, that splitto make TWO in chimps, OR

-Were there TWO shortchromosomes in our ancestor that

fused (joined) to make ONE in humans?

Data Set 4: Human Chromosome 2Discuss in your groups

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We DO have a PROBLEM:“How did this difference happen?”

1. One split to make two, OR

And, we have two hypotheses (testable statements):

Let’s try the second one (fusion). How can we TEST that hypothesis?

2. Two fused (joined) to make one

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We could look for evidence offusion in the middle of our

#2 chromosome…

But, what kind of evidence can we look for?

Well, it so happens that ALL chromosomes have special tip ends, called “telomeres”…

Data Set 5: Examining the DNAA bit of background first

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CHROMOSOME PARTSAll Chromosomes have

telomeres at both ends(like shoelace aglets!)

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HeadTelomere

Centromere

TailTelomere

ttagggttagggttagggttagggttagggttaggg…||||||||||||||||||||||||||||||||||||aatcccaatcccaatcccaatcccaatcccaatccc…

Telomeres have a special DNA sequence…

DNA Sequence for Telomeres:

ttagggttagggttaggg…||||||||||||||||||aatcccaatcccaatccc…

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HeadTelomere

Centromere

TailTelomere

NOTICE:Tandem Repeats in Telomeres:ttagggttagggttaggg…||||||||||||||||||aatcccaatcccaatccc…

Did you notice the repeated sequence: ttaggg?

“ttaggg” is repeated 800-1600 times in each Telomere

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Here’s another view ofa chromosome,

showing the telomeresuntwisted, and their typical

DNA sequence

It also shows that theupper (shorter) arm

above the centromereis called the “p-arm”, andthe lower (longer) arm is

called the “q-arm”

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Here are ends of the upper

telomeres of thechimp’s “short”

chromosome (left)…

Short #2 “Extra”

and its “extra”chromosome (right)

TELOMERE DNA CLOSE-UP

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When we turn the “extra”chromosome upside-

down,and try to connect it to

the“short” chromosome, it

onlyFITS one way (left)…

They do NOT fitwhen one telomere istwisted 180

o (right)

NOTICE!

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FURTHERMORE…When we lay the fusion area on its side,

we can see more clearly how the DNA sequence

changes at the fusion point.

Reading the top strand only, see:

T T A G G G C C C T A A

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THAT’S WHAT YOU WILL BE LOOKING FOR

When you are searching the DNA for the

Fusion Point, you will be lookingat only one strand of DNA

(since the “lower” strand is the predictable

complement of the “upper” strand).Look for something like this:…

ttagggttagggttagggccctaaccctaaccctaa…

Read this like lines of text in a book…Do you see where the multiple g’s (and no c’s) END,

and multiple c’s (and no g’s) BEGIN?

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What would this point be called?(where multiple g’s stop, and

multiple c’s begin)

This would be the FUSION POINTRaise your hand when you see that point

in this actual DNA strand below:

On which line does the change happen?

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Maybe this will show itmore clearly:

GOT THE PICTURE?

THERE’S the FUSION POINT !

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NOW…WHERE should we LOOK

for theFUSION POINT?

YES!Right in the MIDDLE

of our chromosome #2,where the two matching

chimp chromosomesoverlap !

2a

2b

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This would be BELOW theCENTROMERE, in the

“q-arm” of the chromosome,in the region known as

“2q13”,shown in red.

2b

2a

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I have gone to an online DNA databaseand printed out the DNA in that region.You could do this yourself, but, to save

time, I’ve done that for you…

So, where can we see the DNAfrom this region of our

#2 chromosometo examine?

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This 2q13 region gives us

52 pages of DNA!

This is what a page looks like…

On this page, thereare 57 lines, each line with

60 bases (letters),and that gives us…

3,420 bases per page!

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If these 52 pageswere attached

end-to-end,they would stretchabout 14 meters

(16 yards) aroundyour room!

AND… If ALL the DNA from ourENTIRE #2 chromosomewas printed out like this,

it would stretch about16 km (10 miles)!

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By the way…

Each number on the left edge equals the number of the first base (letter)

on that line.

And, a space has been inserted after every 10th base (letter)

to make counting easier.

1 gaattcttgt tctgtattta gaaacccact cacgttactt gatatttggg tatttaagtc 61 atgaaaggta tttcttctag gaagcagtga ttctaaagtg tatgcttaac cagtcagttg121 agtgtctact cttgtgtgtt cacaagtgtg cacaaagttt ttggtaaatt aagaatatta181 tttcaaataa attaatttca tccccatagg agccagttta tcagataatt catttttcat241 ttctgcaaat caatacacaa tgagctcata ttcagataaa tataatagtt tttctttatt

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You may noticewhen you are searching, that

the “ttaggg” patternis not perfect!

An occasional “c”slips in here and there,and you will see other

minor “glitches.”WHY?

If you said“MUTATIONS,”

you would be right.

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NOW, it’s YOUR turn! You get to SEARCH those 52 pages!

Are you ready???Just kidding!

Actually, you will formteams of 5, and

each team will search together(from the

“2q13” region)

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Each person looks forthat “Fusion Area” on

a different page.

When one of you findsit, show your partners.

Discuss your discovery with your partners, and answer the questions on your “SEARCH” worksheet

One of those pagesshould have the“Fusion Area”

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RECAPPROBLEM: How did our #2 chromosome

come to look identical to two chromosomesin chimpanzees”

TEST: Look for fusion evidencein the form of telomere DNA

in the middle of our #2chromosome

PREDICTIONS: If hypothesis is true, we should find two telomeres there;

If NOT true, should be NO telomeres there.

HYPOTHESIS: our #2 chromosome

was formed by the fusion oftwo chromosomes in an

ancestor, after chimps branched off.

Chimp Us

<--Common Ancestor

Fusion?

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GOSEARCHfor the

Tell-Tale Telomeres !

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Students search DNA in groups

Data Set 5: Searching the DNA

Part 3

DNA Search Lab Followup

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Welcome back from yourSEARCH FOR

THE TELL-TALE TELOMERE

Let’s see what it tells us…

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108061 agcacagacc tgggggtcac cgtaaaggtg gagcagcatt cccctaagca cagaggttgg 108121 ggccactgcc tggctttgtg acaactcggg gcgcatcaac ggtgaataaa atctttcccg 108181 gttgcagccg tgaataatca aggttagaga ccagttagag cggttcagtg cggaaaacgg 108241 gaaagaaaaa gcccctctga atcctgggca gcgagattct cccaaagcaa ggcgaggggc 108301 tgcattgcag ggtgagggtg agggttaggg tttgggttgg gtttggggtt ggggttgggg 108361 taggggtggg gttggggttg gggttggggt taggggtagg ggtaggggta ggggtagggt 108421 cagggtcagg gtcagggtta gggttttagg gttaggattt tagggttagg gtaagggtta 108481 agggttgggg ttggggttag ggttaggggt tagggttggg gttggggttg gggttggggt 108541 tggggttggg gttagggtta gctaaaccta accctaaccc ctaaccccaa ccccaacccc 108601 aaccctaccc ctacccctac ccctaacccc aacccccacc cttaaccctt aacccttacc 108661 ctaaccctaa cccaaaccct aaccctaccc taaccctaac ccaaccctaa ccctaaccct 108721 accctaaccc taacacccta aaaccgtgac cctgaccttg accctgaccc ttaaccctta 108781 accctaacca taaccctaaa ccctaaccct aaaccctaac cctaaaccct aaccctaaca 108841 ctaccctacc ctaaccccaa cccctaaccc ctaaccctaa ccctacccct aaccccaacc 108901 ccagccccaa cccttaccct aaccctaccc taacccttaa ccctaacccc taaccctaac 108961 ccctaaccct aaccctaccc caaccccaaa cccaacccta acccaaccct aacccctaac 109021 cctaacccct accctaaccc ctagccctag ccctagccct aaccctaacc ctcgccctaa 109081 ccctcaccct aaccctcacc ctcaccctaa cccaacgtct gtgctgagaa gaatgctgct 109141 ccgcctttaa ggtgcccccc aggtctgtgc tgaacagaac gcagctccgc cgtcgcagtg 109201 ccctcagccc gcccgcccgg gtctgacctg agaagaactc tgctccgcct tcgcaatagc 109261 cccgaagtct gtgcagagga gaacgcagct ccgccctcgc gatgctctcc ggctgtgtgc 109321 taaagagaac gcaactccgc cctcgcaaag gcggcgcgcc ggcggaggcg cggagaggcg

RESULTS: Can you see the telomeres?

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RESULTS CLARIFIED:108061 agcacagacc tgggggtcac cgtaaaggtg gagcagcatt cccctaagca cagaggttgg 108121 ggccactgcc tggctttgtg acaactcggg gcgcatcaac ggtgaataaa atctttcccg 108181 gttgcagccg tgaataatca aggttagaga ccagttagag cggttcagtg cggaaaacgg 108241 gaaagaaaaa gcccctctga atcctgggca gcgagattct cccaaagcaa ggcgaggggc 108301 tgcattgcag ggtgagggtg agggttaggg tttgggttgg gtttggggtt ggggttgggg 108361 taggggtggg gttggggttg gggttggggt taggggtagg ggtaggggta ggggtagggt 108421 cagggtcagg gtcagggtta gggttttagg gttaggattt tagggttagg gtaagggtta 108481 agggttgggg ttggggttag ggttaggggt tagggttggg gttggggttg gggttggggt 108541 tggggttggg gttagggtta gctaaaccta accctaaccc ctaaccccaa ccccaacccc 108601 aaccctaccc ctacccctac ccctaacccc aacccccacc cttaaccctt aacccttacc 108661 ctaaccctaa cccaaaccct aaccctaccc taaccctaac ccaaccctaa ccctaaccct 108721 accctaaccc taacacccta aaaccgtgac cctgaccttg accctgaccc ttaaccctta 108781 accctaacca taaccctaaa ccctaaccct aaaccctaac cctaaaccct aaccctaaca 108841 ctaccctacc ctaaccccaa cccctaaccc ctaaccctaa ccctacccct aaccccaacc 108901 ccagccccaa cccttaccct aaccctaccc taacccttaa ccctaacccc taaccctaac 108961 ccctaaccct aaccctaccc caaccccaaa cccaacccta acccaaccct aacccctaac 109021 cctaacccct accctaaccc ctagccctag ccctagccct aaccctaacc ctcgccctaa 109081 ccctcaccct aaccctcacc ctcaccctaa cccaacgtct gtgctgagaa gaatgctgct 109141 ccgcctttaa ggtgcccccc aggtctgtgc tgaacagaac gcagctccgc cgtcgcagtg 109201 ccctcagccc gcccgcccgg gtctgacctg agaagaactc tgctccgcct tcgcaatagc 109261 cccgaagtct gtgcagagga gaacgcagct ccgccctcgc gatgctctcc ggctgtgtgc 109321 taaagagaac gcaactccgc cctcgcaaag gcggcgcgcc ggcggaggcg cggagaggcg

HeadTelomereof “extra”chrom. 2a

HeadTelomereof “short”chrom. 2b

FUSION POINT !

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108361 taggggtggg gttggggttg gggttggggt taggggtagg ggtaggggta ggggtagggt 108421 cagggtcagg gtcagggtta gggttttagg gttaggattt tagggttagg gtaagggtta 108481 agggttgggg ttggggttag ggttaggggt tagggttggg gttggggttg gggttggggt 108541 tggggttggg gttagggtta gctaaaccta accctaaccc ctaaccccaa ccccaacccc 108601 aaccctaccc ctacccctac ccctaacccc aacccccacc cttaaccctt aacccttacc 108661 ctaaccctaa cccaaaccct aaccctaccc taaccctaac ccaaccctaa ccctaaccct 108721 accctaaccc taacacccta aaaccgtgac cctgaccttg accctgaccc ttaaccctta

Did you know… you’ve got FOSSILS in YOU !

All of you have these fossils,in the #2 chromosome of every cell !

Fossils are the remains of ancient life,and these are the telomeres of

two chromosomes from your ancient ancestor !

So, these telomeres are your very ownMOLECULAR FOSSILS !

Telo.2a

Telo.2b

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PREDICTIONS: If our hypothesis was true, we should find two telomeres there;

If NOT true, should be NO telomeres there.

Did we find telomeres there?

YES! Therefore…

Our hypothesis was supported:Our #2 chromosome WAS formed

from the FUSION of two chromosmesin an ancient ancestor after the

chimpanzees branched off.

CONCLUSION

A Peek at the Chromosomes

of Other Apes…

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On the next slide, you will see thechromosome diagrams for humans,

chimpanzees, gorillas, and orangutans,all the :”Great Apes”

They are shown side by side for easy comparison…

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The Chromosomesof Humans and Apes

Compared

For each number,the chromosomesare arranged in

this order(left to right):

human, chimpanzee,gorilla, orangutan

What is moststriking?

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RIGHT! They are ALL

Strikingly Similar!

And what do we knowwhen we find identical

or very similar patternson different items?

RIGHT!They had to have aCOMMON ORIGIN

Or, in this case…COMMON ANCESTRY

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Based on these chromosome comparisons…Biologists have been able to draw

a phylogenetic tree, showinghow primates are related to each other.

The following slide shows the tree(called a “Primate Cladogram”).

See if you can point to where the COMMON ANCESTORS

of Modern Primates would be LOCATED on the tree…

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Chimps Humans

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Did you find ALLof the

Common Ancestors?

Chimps

Humans

Did you notice…

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All the other apes had that“extra” chromosome, too?

This confirms that this isthe more PRIMITIVE (original)CONDITION, so our SINGLE#2 chromosome is the DERIVED CONDITION(the result of fusion)

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When we compare primates by using other features,

including DNA, different proteins, anatomy, physiology, and fossils,

Biologists have developed similarCladograms (Phylogenetic Trees),

like these…

MORE CONFIRMING EVIDENCE

See how similarthey are?

Based on Albumin Protein Analysis:

Based on DNA Hybridization Analysis

And here’s another one…

PRIMATE CLADOGRAM

Based on Genome Analysis

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Humans

BonobosChimpanzees

Gorillas

Orangutans

Gibbons

Old WorldMonkeys

6 mya

8 mya

13 mya

18 mya

25-30 mya

SpeciesToday

Common Ancestor

Again, basically the same pattern

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When all the data point to essentially the same conclusions,

this strengthens those conclusions.

Biologically, humans are very closely related to the apes.

In fact, chimps are closer to US,than they are to gorillas!

Humans and chimps are even closer than zebras are to horses!

Biologists have even recommended thathumans and chimps be in the same genus!

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This may be hard for many to accept…But we are very special apes,

not just “ordinary animals.”

Because of our brain and our dexterity,humans have built amazing cultures

and environments not equaledanywhere else in the animal kingdom.

LESSON WRAP-UPREALITY-CHECK QUESTIONS

MORE DNA SEARCHES

Time for a REALITY CHECK Number your paper from 1-8 Based on the observed data…

Which are true… which are false?1. All chromosomes have telomeres at both ends.

2. All chromosomes have telomeres in their middles.

3. Identical complex patterns on different items means they had a common origin.

4. A hypothesis is a prediction.

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REALITY CHECK cont. Which are true… which are false?

5. Our #2 chromosome was formed by the fusion of 2 chromosomes in an early ancestor.

6. Humans evolved from monkeys.7. Humans evolved from chimpanzees.8. Humans & chimpanzees evolved from a

common ancestor.

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Confirmation: More Evidence

When we compare

ALL the DNA inour #2

chromosomewith ALL the DNA

in the two chimp

chromosomes…*

we find that it isall the same

DNA !

*(this is “synteny”)

However…

When we compareALL the DNA in

our #2 chromosomewith DNA in Dogchromosomes…

we find that our #2is a patchwork of DNA

from 8 differentDog chromosomes!

(WHY?)

If you said“More time since we

branched from ourCOMMON ANCESTOR

with dogs,SO, more time for

more chromosomechanges and other

mutations,”YOU GOT IT!

WHY?

JUST SO WE’RE CLEAR, THIS IS JUST ONE OF MANY PIECES OF EVIDENCE FOR A RELATIONSHIP BETWEEN CHIMPS & HUMANS

Telomere Tid-Bits

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1. Telomeres apparently protect the endsof our chromosomes, keeping the gene-DNAfrom getting damaged.2. Each time our chromosomes replicateand cells divide, a little of each telomereis lost, so they get shorter as we age!

3. This is one reason why embryonic stem cellsare preferred over adult stem cells instem cell research.

More Telomere Tid-Bits

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4. There is an enzyme, telomerase, that canreplace some of the missing telomere DNA. It’s thought that defective telomerasecould be a cause of aging problems.

5. Telomeres and telomerase are the subjects ofmuch research into cancer, heart disease,brain function, and other problems of aging.

KEY TO REALITY CHECK

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1. All chromosomes have telomeres at both ends.

True 2. All chromosomes have telomeres in their middles.

False3. Identical complex patterns on different items means they had a common origin.

True4. A hypothesis is a prediction.

False

KEY TO REALITY CHECK (cont.)

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5. Our #2 chromosome was formed by the fusion of 2 chromosomes in an early ancestor.

True6. Humans evolved from monkeys.

False7. Humans evolved from chimpanzees.

False8. Humans & chimpanzees evolved from a common ancestor.

TRUE!