1. AP Bio Review Day 2

2. Warm Up
Discuss three specific ways speciation can occur by providing an example. Describe how scientists can determine if speciation has occurred.

3. Allopatric vs. Sympatric Speciation
Allopatric speciation-Speciation occurs because a given group has been separated from the parent group, usually because of a geographic separation as time goes by.
Sympatric speciation-speciation occurs even though the two groups are still living in the same area.
Graphic-Campbell
From Latin: Allo = “different” and Patric = Father (meaning “fatherland” in this case), so Allopatric translates as “different fatherland” meaning the varieties evolved in different geographical locations.
Sym = “same” so Sympatric translates as “same fatherland”

4. Allopatric Speciation
First, geographic isolation occurs. This is an extrinsic isolating mechanism.
The two populations must become isolated geographically from one another.
If the groups become sympatric again one of two things result…
Graphic-Campbell
An extrinsic is a property is one that is not dependent on the organism in question. It is an external factor.

5. Allopatric Speciation
They become separate species, as evidenced by the fact they can no longer interbreed.
They can still interbreed, thus they remain the same species.
Islands produce some of the most profound examples of speciation due to geographic isolation.

6. Sympatric Speciation: Polyploidy
Polyploidy refers to instant speciation which occurs in most often in plants.
Polyploid cells and organisms are those containing more than two paired (homologous) sets of chromosomes.
Polyploidy may occur due to abnormal cell division, either during mitosis, or commonly during metaphase I in meiosis.
Review the concept of nondisjunction of chromosomes during meiosis.
True polyploidy rarely occurs in humans, although it occurs in some tissues (especially in the liver). Aneuploidy is more common.
Polyploidy occurs in humans in the form of triploidy, with 69 chromosomes (sometimes called 69,XXX), and tetraploidy with 92 chromosomes (sometimes called 92,XXXX). Triploidy, usually due to polyspermy, occurs in about 2–3% of all human pregnancies and ~15% of miscarriages.[citation needed] The vast majority of triploid conceptions end as miscarriage and those that do survive to term typically die shortly after birth. In some cases survival past birth may occur longer if there is mixoploidy with both a diploid and a triploid cell population present.

7. Sympatric Speciation: Polyploidy
Autopolyploidy refers to the occurrence in which the number of chromosomes double in the offspring due to total non-disjunction during meiosis.
This was discovered by Hugo deVries when studying primroses.
He noticed some of them were larger

8. Sympatric Speciation: Polyploidy
The normal primrose is diploid with 14 chromosomes. 2N = 14
In this species there was a total nondisjunction event resulting in primroses that are tetraploid. 4N = 28
These primroses cannot successfully mate with the diploid species.

9. Adaptations and Fitness
An adaptation is a genetically controlled trait that is favored by natural selection and gives the organism a reproductive advantage ensuring the trait is passed on to its descendants.
This trait may also allow the individual to survive longer thus increasing the reproductive rate of that individual.
Compare and contrast these hares and identify the differences in their traits
Ask students to compare these two hares and identify the differences in their traits. The students should come up with coat color, length of ears, length of limbs, body shape, etc.

10. Adaptations and Fitness
The antelope hare lives in the desert, and the snowshoe hare lives in the mountains.
Explain how the differences in their traits enhance their ability to survive in their respective environments.
Evolutionary success or fitness refers to the contribution of genes to the gene pool and NOT how long an organism lives.
It’s one thing to “identify” traits and yet another to explain their importance or implication!
The long limbs of the antelope hare help dissipate body heat and keep the hare cool. The brown coat color helps it to blend in with its environment, thus be less obvious to potential predators. The snowshoe hare has smaller ears and shorter limbs with a rounder body. This helps keep the hare warmer. The white coat color helps it to also blend in with its environment.

11. The Effect of Environmental Change
Earth’s environment is NOT STATIC, but rather ever changing.
As a consequence, traits or adaptations that were favorable may become unfavorable.
The peppered moth, Biston betularia is native to England and exists in two forms, one is dark and the other light with a “peppered” appearance. Birds are its main predator.
Prior to the industrial revolution, only 2% of the moths were dark.
The industrial revolution produced vast amounts of sulfur dioxide and soot from the burning of coal which altered the environment.
Fifty years later 95% of the moths were dark.
Propose an explanation!
Environmental changes often cause a shift in selection pressures. Traits that were once beneficial to a population of organisms may become detrimental and vice versa.

12. Industrial Melanism
England has since regulated the burning of coal and as a result, the trees are returning to their original state (A).
Consequently, the coloring among the population of moths in Britain has shifted back so that the peppered moths are once again favored.
Explanation: The trees were previously light and covered in lichens, thus peppered moths had the advantage of camouflage over dark moths. (You may have to point out the peppered moth near the top of photo A.)
The SO2 gas produced from the industrial revolution killed the lichens. Furthermore, the soot produced during the burning of coal collected on tree trunks changing their appearance and darkening them. As a result, the darker moth is now more camouflaged and less likely to be eaten by birds.

13. Evolution Defined
Evolution is defined as a change in the inherited characteristics of biological populations over successive generations.
More simply: Genetic change over time
Evolutionary processes give rise to diversity at every level of biological organization, from the molecular to the macroscopic.
As a result diversity is prevalent among molecules such as DNA as well as individual organisms and species of organisms.
Students need to be clear on the approaching definitions and distinctions AND have some illustrative examples they can discuss on the AP Exam.

14. Microevolution
Microevolution is simply a change in gene frequency within a population.
Evolution at this scale can be observed over short periods of time such as from one generation to the next.
Example: The frequency of a gene for pesticide resistance in a population of crop pests increases.
Predict some reasons why these changes would come about
Remind students that a gene is a sequence of DNA nucleotides that specify a particular polypeptide chain and that genes code for proteins.
Have students generate an example for each of the 4 example “causes” of microevolution. Many correct answers are possible!
natural selection favored the gene (sickle cell anemia & malaria)
the population received new immigrants carrying the gene (light skinned population crosses with dark skinned population resulting in hybrids)
some nonresistant genes mutated to the resistant version (natural immunities to disease among populations)
because of random genetic drift from one generation to the next (founder effect)

15. Microevolution
Microevolution is simply a change in gene frequency within a population.
Evolution at this scale can be observed over short periods of time such as from one generation to the next.
Example: The frequency of a gene for pesticide resistance in a population of crop pests increases.
Such a change might come about because
natural selection favored the gene
the population received new immigrants carrying the gene (gene flow)
nonresistant genes mutated into a resistant version of the gene
of random genetic drift from one generation to the next
Remind students that a gene is a sequence of DNA nucleotides that specify a particular polypeptide chain and that genes code for proteins.
Have students generate an example for each of the 4 example “causes” of microevolution. Many correct answers are possible!
natural selection favored the gene (sickle cell anemia & malaria)
the population received new immigrants carrying the gene (light skinned population crosses with dark skinned population resulting in hybrids)
some nonresistant genes mutated to the resistant version (natural immunities to disease among populations)
because of random genetic drift from one generation to the next (founder effect)

16. Microevolution
A gene is a sequence of DNA nucleotides that specify a particular polypeptide chain.
Genes code for proteins.
An allele is a particular form of a gene. For example: B represents the allele for black coat color and b for white coat color.
Selection acts on phenotype because differential reproduction and survivorship depend on phenotype not genotype.
Natural selection acts on individuals, but only populations evolve.
Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question!

17. More Evolution Terms
Species-a group of interbreeding organisms that produce viable and fertile offspring in nature
Gene pool-sum total of all the genes in a given species
Allelic frequency-is the percent occurrence for a given allele

18. Phylogenetic Trees
Phylogeny is the study of the evolutionary relationships among a group of organisms.
A phylogenetic tree is a construct that represents a branching “tree-like” structure which illustrates the evolutionary relationships of a group of organisms.
Phylogenies are based on
Morphology and the fossil record
Embryology
DNA, RNA, and protein similarities
The importance of students understanding cladograms and phylogenetic trees cannot be over emphasized. Many biologist use them interchangeably. The subtle difference is cladogram is used to represent a hypothesis about the evolutionary history of a group of organisms. A phylogenetic tree represents the true evolutionary history of a group of organisms.

19. Phylogenetic Trees Basics
Phylogenies can be illustrated with phylogenetic trees or cladograms. Many biologist use these constructs interchangeably.
A cladogram is used to represent a hypothesis about the evolutionary history of a group of organisms.
A phylogenetic tree represents the “true” evolutionary history of the organism. Quite often the length of the phylogenetic lineage and nodes correspond to the time of divergent events.
This slide is simply explaining some phylogenetic tree basics. Explain that a node may occur because the group was divided in two by geographic isolation. Since they are no longer together, they are experiencing the “founder effect”, different selection pressures, and different mutations.

20. Phylogenetic Trees of Sirenia and Proboscidea
Point out to students that elephants are closely related to manatees. Also, that manatees are more closely related to elephants than they are to seals and walruses. Pinnidpedia (a widely distributed and diverse group of fin-footed marine mammals which are semiaquatic) are more closely related to bears and are carnivores. Manatees, like elephants, are herbivores. Additionally, emphasize that phylogenetic trees and cladograms can be oriented vertically or horizontally.
This phylogenetic tree represents the “true” evolutionary history of elephants. The nodes and length of a phylogenetic lineage indicate the time of divergent events. Also any organism not shown across the top of the page is an extinct species.

21. Traditional Classification and Phylogenies
This phylogenetic tree is a reflection of the Linnaean classification of carnivores, however with the advancements in DNA and protein analysis, changes have been made in the traditional classification of organisms and their phylogeny.
For example, birds are now classified as true reptiles.
Emphasize that classification began by using only physical traits and quite often that was a reflection of the phylogeny of the organisms . Subsequent use of both embryology and biochemistry evidence has caused changes in such phylogenies and often results in changing classifications.

22. Taxa
Graphic from Campbell
Be aware this unit introduces a lot of vocabulary such as polytomy. Explain polytomy is understood to be temporary, since the hope is that sometime future evidence will resolve the polytomy. The resolution will determine which group evolved from which group.
Also note that nodes have only two branches versus polytomy which have more than two branches.
A taxon is any group of species designated by name. Example taxa include: kingdoms, classes, etc. Every node should give rise to two lineages. If more than two linages are shown, it indicates an unresolved pattern of divergence or polytomy.

23. Sister Taxa
Sister taxa are groups or organisms that share an immediate common ancestor. Also note the branches can rotate and still represent the same phylogeny.

24. Definition of a clade
A clade is any taxon that consists of all the evolutionary descendants of a common ancestor
Each different colored rectangle is a true clade.
Students need a clear understanding of cladistics. (Graphic: Understanding Evolution web site.)

25. Molecular Clocks
The molecular clock hypothesis states: Among closely related species, a given gene usually evolves at reasonably constant rate.
These mutation events can be used to predict times of evolutionary divergence.
Therefore, the protein encoded by the gene accumulates amino acid replacements at a relatively constant rate.
Graphic Campbell 8th edition.
Here’s a nice reference website:

26. Molecular Clocks
The amino acid replacement for hemoglobin has occurred at a relatively constant rate over 500 million years.
The slope of the line represents the average rate of change in the amino acid sequence of the molecular clock.
Different genes evolve at different rates and there are many other factors that can affect the rate.
Student may have to interprets molecular clocks on the AP exam. They should know that a linear graph represents a constant rate of change and that the slope of the line allows them to predict how many amino acids would change over a given time span.
Ask the students to predict how many amino acid would be changed if 800 million years had passes by. (ANSWER: about 1.4—use a simple proportion, if 500 million years resulted in about 0.85 AA differences, then (800 x 0.85) ÷ 500 = 1.36 AA differences OR you can use points (0,0) and (500, 0.9) and use the 2-point slope formula to obtain the slope, then plug into y=mx + b and solve. Student’s know this lingo from math class! ) Either way, you arrive at about 1.4 AA differences.
Graphic

27. Molecular Clocks

28. Molecular Clocks
Molecular clocks can be used to study genomes that change rather quickly such as the HIV-1 virus (a retrovirus).
Using a molecular clock, it as been estimated that the HIV-1 virus entered the human population in 1960’s and the origin of the virus dates back to the 1930’s.

29. Making a Cladogram Based on Traits
Examine the data given.
Propose a cladogram depicting the evolutionary history of the vertebrates.
The lancet is an outgroup which is a group that is closely related to the taxa being examined but is less closely related as evidenced by all those zeros!
The taxa being examined is called the ingroup.
Let the students use information in the table and construct a cladogram. Tell the student that using a 1 vs. a 0 is simply one convention with regard to presenting the data. Sometimes + and - are used or perhaps an X and nothing at all in the table.

30. Making a Cladogram Based on Traits
Note that each trait exists only after the group divides into two.
Graphic from Campbell.