More Historical More Historical EvidenceEvidence

The study of HomologiesThe study of Homologies

HomologyHomology

►What does the word What does the word HomologousHomologous mean?mean?

►Homology is the study of Homology is the study of similarity similarity between organismsbetween organisms

►There are three major branches of There are three major branches of homology:homology: Anatomical HomologyAnatomical Homology Embryological HomologyEmbryological Homology Molecular HomologyMolecular Homology

Anatomical HomologyAnatomical Homology

► Outwardly, these Outwardly, these look like very look like very different structures.different structures.

Beneath The Surface…Beneath The Surface…

Strange Coincidence?Strange Coincidence?

► At a structural level, the wing of a bat, a At a structural level, the wing of a bat, a human arm and a whale’s flipper all share the human arm and a whale’s flipper all share the same number, type and location of bones, same number, type and location of bones, suggesting thatsuggesting that THEY MAY SHARE COMMON THEY MAY SHARE COMMON ANCESTRYANCESTRY

► 'What can be more curious than that the hand 'What can be more curious than that the hand of a man, formed for grasping, that of a mole of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat should the porpoise, and the wing of the bat should all be constructed on the same pattern and all be constructed on the same pattern and should include similar bones in the same should include similar bones in the same relative position?'relative position?' (Charles Darwin) (Charles Darwin)

Vestigial StructuresVestigial Structures

► Some organisms have structures that appear Some organisms have structures that appear to be useless relics of the past to be useless relics of the past

► Suggests that these organisms may be Suggests that these organisms may be descended from ancestral organisms in descended from ancestral organisms in which the structure IS still useful!which the structure IS still useful!

Evidence of EvolutonEvidence of Evoluton►Analogous StructuresAnalogous Structures: structures similar in : structures similar in

function, but not inherited from a common function, but not inherited from a common ancestor.ancestor.

►Same function, different structureSame function, different structure

Embryological HomologyEmbryological Homology

► The diagram below shows embryos of five The diagram below shows embryos of five different species: pig, chicken, fish, turtle, different species: pig, chicken, fish, turtle, and human. Can you tell which is which?and human. Can you tell which is which?

Figured it out yet?Figured it out yet?

How about now?How about now?

Did you guess correctly?Did you guess correctly?

Embryological HomologyEmbryological Homology

► Did you know that when you were inside your mother’s Did you know that when you were inside your mother’s womb, for a while you looked almost exactly like a fish?womb, for a while you looked almost exactly like a fish?

► Vertebrate embryos all share a Vertebrate embryos all share a similar pattern of similar pattern of developmentdevelopment, suggesting that they may share common , suggesting that they may share common ancestryancestry

Human – 31 days

Chicken – 2 ½ days

Pig – 21 days

Molecular HomologyMolecular Homology

►All living things contain DNA and RNA.All living things contain DNA and RNA.

►Changes in Proteins, DNA and RNA can be Changes in Proteins, DNA and RNA can be traced from ancestors to their descendents.traced from ancestors to their descendents.

►The fewer Amino Acid differences between The fewer Amino Acid differences between organisms, the closer their inferred organisms, the closer their inferred evolutionary relationship.evolutionary relationship. Hemoglobin and Cytochrome C are a Hemoglobin and Cytochrome C are a

group of proteins that are commonly group of proteins that are commonly found in found in manymany different organisms different organisms

Proteins & Amino AcidsProteins & Amino Acids

► Proteins (eg. Hemoglobin, Cytochrome c) can Proteins (eg. Hemoglobin, Cytochrome c) can exist in subtly different forms, depending on exist in subtly different forms, depending on their specific Amino Acid configurationtheir specific Amino Acid configuration

Apple Protein

Celery Protein

Our Chimpanzee Our Chimpanzee “Cousins”?“Cousins”?

►Comparison of Comparison of chimp and human chimp and human chromosomes chromosomes reveals reveals manymany similaritiessimilarities

►Could we be Could we be related by related by common common descent?...descent?...

Example: the Evolutionary Hypothesis

of Common Ancestry

Chromosome Numbers in the great apes:

human (Homo) 4646chimpanzee (Pan) 48gorilla (Gorilla) 48orangutan (Pogo) 48

Testable prediction:Testable prediction: If these organisms share common ancestry, the human genome must contain a fused chromosome.

Testable prediction:Testable prediction: If these organisms share common ancestry, the human genome must contain a fused chromosome.

Comparing ChromosomesComparing Chromosomes

► The banding patterns on The banding patterns on stained chromosomes stained chromosomes show regions of tightly show regions of tightly condensed (condensed (darkdark) and ) and loosely condensed loosely condensed ((palepale) Histone proteins) Histone proteins

► Protein location is Protein location is dependent on gene loci, dependent on gene loci, and the bands can and the bands can therefore be used to therefore be used to infer genetic similarityinfer genetic similarity

► How similar would you How similar would you expect our banding expect our banding pattern to be, compared pattern to be, compared to Chimpanzees?to Chimpanzees?

Human vs. Human vs. Chimp Chimp

ChromosomChromosomeses

• Human chrom. are on the left

• Chimp’s are on the right

• Notice that Human Chromosome #2 appears to be a combination of Chimp Chromosomes #2 & 3

Chromosome Numbers in the great apes

(Hominidae):

human (Homo) 46chimpanzee (Pan) 48gorilla (Gorilla) 48orangutan (Pogo) 48

Testable prediction:Testable prediction: The marks of that fusion must appear in one of the human chromosomes.

CentromereTelomere

Ancestral Chromosomes

Fusion

Homo sapiens

Centromere #1

Telomere sequences

Centromere #2

“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two acrocentric chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1 (ref. 2; hg 16:114455823 – 114455838), where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22 (Fig. 3; Supplementary Fig. 3a, region A). During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated (42).”Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.

“Chromosome 2 is unique to the human lineage of evolution, having emerged as a result of head-to-head fusion of two acrocentric chromosomes that remained separate in other primates. The precise fusion site has been located in 2q13–2q14.1 (ref. 2; hg 16:114455823 – 114455838), where our analysis confirmed the presence of multiple subtelomeric duplications to chromosomes 1, 5, 8, 9, 10, 12, 19, 21 and 22 (Fig. 3; Supplementary Fig. 3a, region A). During the formation of human chromosome 2, one of the two centromeres became inactivated (2q21, which corresponds to the centromere from chimp chromosome 13) and the centromeric structure quickly deterioriated (42).”Hillier et al (2005) “Generation and Annotation of the DNA sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.

Homo sapiens

Inactivated centromere

Telomere sequences

What do YOU think about this information…?What do YOU think about this information…?

Human Chromosome #2 shows the exact point at which this fusion appears to have

taken place

Human Chromosome #2 shows the exact point at which this fusion appears to have

taken place

What do you think…?What do you think…?

Darwin had NO IDEA about Chromosomes – does this new information SUPPORT his evolutionary hypothesis, or NOT…?

Present-Day Evidence Present-Day Evidence For EvolutionFor Evolution

““Observing Evolution In Action”Observing Evolution In Action”

Natural SelectionNatural Selection

► Is there any evidence of Natural Is there any evidence of Natural Selection taking place in real Selection taking place in real populations?populations?

►One study, performed during the One study, performed during the industrial revolution in England, industrial revolution in England, demonstrated that populations of demonstrated that populations of organisms ARE greatly affected by organisms ARE greatly affected by environmental changesenvironmental changes

The Peppered MothThe Peppered Moth

► Two different forms of the moth existedTwo different forms of the moth existed► One Dark form, one LightOne Dark form, one Light► Both forms were commonBoth forms were common

Antibiotic ResistanceAntibiotic Resistance

►Because Bacteria reproduce so Because Bacteria reproduce so quickly, they represent excellent quickly, they represent excellent specimens for testing Natural specimens for testing Natural SelectionSelection

►Watch how quickly they can “evolve” because of Natural Selection…

Examples of Evolution at Examples of Evolution at WorkWork

Speciation (formation of a new Speciation (formation of a new species)species)

► results from results from reproductive isolationreproductive isolation - when - when members of two ancestral populations can members of two ancestral populations can no longer interbreed to produce fertile no longer interbreed to produce fertile offspringoffspring

► How do populations get isolated?....How do populations get isolated?....

Behavioral IsolationBehavioral Isolation

Two populations are capable Two populations are capable of interbreeding but have of interbreeding but have differences in courtship differences in courtship

rituals.rituals.

Eastern Meadowlark Western Meadowlark

Both birds are in thesame geographic range but

they have a differentmating song

Isolating Mechanisms

Isolating Isolating MechanismsMechanisms

Geographic IsolationGeographic Isolation

Two populations separated Two populations separated by geographic barriers like by geographic barriers like

rivers, and mountainsrivers, and mountains

Abert squirrel Kaibab squirrel

Colorado river separatedthis species into two

separate populations. A new subspecies formed –

the Kaibab squirrel

Isolating Isolating MechanismsMechanisms

Temporal IsolationTemporal Isolation

Individual varieties of an Individual varieties of an organism may breed at organism may breed at

different times of day/yeardifferent times of day/year

Ex. Orchids in a rainforestEx. Orchids in a rainforest