Evolution and Biodiversity


Evolutionary Biology (8%)
  1. Early evolution of life
  2. Evidence for evolution
  3. Mechanisms of evolution

Diversity of Organisms (8%)

  1. Evolutionary patterns
  2. Survey of the diversity of life
  3. Phylogenetic classification
  4. Evolutionary relationships

JFMcL. Lynn Margulis endosymbiotic theory is widely used to explain the evolution of eukaryotic cells.
Click on the link below to watch a short tutorial on endosymbiosis.
As you watch, write down 4 different pieces of evidence which support this theory.


RP. When studying evolution and evidence for it, scientists will often study the structures of various organisms. Two differents kinds of structures that are easily mixed up are homologous structures and analogous structures. Homologous structures are anatomical signs of evolution that show a common ancestor. An example being the bones in the human hand are similar to those in the wing of a bat or the flipper of a whale.limbs.jpg

Analogous structures show convergent evolution, or different species evolving and having similar traits. An example could be the wing of a fly and the wing of a bird. Although both are capable of flight, their structures are very different.

LJ: After taking the diagnostic test, I realized that I completely forgot how to do Hardy-Weinberg Equations
Hardy-Weinberg Law
  • A large population
  • Random mating
  • No natural selection
  • No mutations
  • No movement in/out of population

P + Q = 1

P= dominant allele frequency
Q= recessive allele frequency

P2 + 2pq + Q2 =1

P2 = Frequency of homozygous dominant
2pq= Frequency of heterozygous
Q2 =Frequency of homozygous recessive

(Typically, you are given the Q2 value, to solve take its square root (q) and plug it into P + Q = 1 and find the P value. Then, plug these values into the second formula)
here is a website with some practice problems
JFMcL. You weren't the only one! Good topic for review! That's the purpose of those diagnostic tests.

I had a lot of trouble remembering each phylum of animals for evolution. I found this website, which gives a short and concise summary of each phylum.
external image loadBinary.aspx?filename=YB010930FG0010.gif

LJ: This helps explain phylogenetic trees.


How Does Genetic Variation Occur in a Population?

Genetic variation occurs through sexual reproduction. Due to the fact that environments are unstable, populations that are genetically variable will be able to adapt to changing situations better than those that do not contain genetic variations.
Sexual reproduction allows for genetic variations to occur through genetic recombination.
Recombination occurs during [[/od/meiosis/a/aa022406a.htm|meiosis]] and provides a way for producing new combinations of alleles on a single chromosome. Independent assortment during meiosis allows for an indefinite number of combinations of genes
Sexual reproduction makes it possible to assemble favorable gene combinations in a population or to remove unfavorable gene combinations from a population. Populations with more favorable genetic combinations will survive in their environment and reproduce more offspring than those with less favorable genetic combinations

The following site helped to explain the different types of isolation such as reproductive and geographic.


external image 500px-Undiscovered_species_chart.png
I had trouble distinguishing between stabalizing, directional, and disruptive selection and this page explains the differences.

Evidence for Evolution
This site goes over fossils and carbon dating.


external image AnimalPhylo_morph.JPG

"Genetic drift is the unpredictable fluctuation in allelic frequencies from one generation to the next." This can be found on page 157 of the review book. Two important types of genetic drift that can seem somewhat confusing are the founder and the bottleneck effects.

The founder effect occurs when a few individuals become isolated from their larger population:
The bottleneck effect is caused by a sudden change in the environment, due to some sort of catastrophe:
Since the surviving individuals above were primarily blue, the next generation will primarily have this trait as well.

In class, I have found that I do not completely understand the concepts of the coelom.

The main functions of the coelom, as found on page 188 of the review book, are:
1. Act as a cushion for organs suspended within the body
2. Act as a hydrostatic skeleton
3. Allow organs to move independently within the body, as well as growing

The organisms can have either be coelomates, pseudocoelomates, or aceolomates.

This section confused me because there are so many terms and so much information but I made this chart so hopefully it is a little simpler all written out here in a chart :)
Porifera (sponges)
Lack true tissues; have choanocytes (collar cells-unique flagellated cells that ingest bacteria and tiny food particles)
Cnidaria (hydras, jellies, sea anemones, corals)
Unique stinging structure (cnidae), each housed in a specialized cell (cnidocyte); gastrovascular cavity (digestive compartment with a single opening)
Platyhelmithes (flatworms)
Dorsoventrally flattened, unsegmented acoelomates; gastrovascular cavity, or no digestive tract
Rotifera (rotifers)
Pseudocoelomates with alimentary canal (digestive tube with mouth and anus); jaw (trophy) in pharynx; head with ciliated crown
Lophophorates: Ectoprocta, phoronida, brachiopoda
Coelomates with lophophores (feeding structures bearing ciliated tentacles)
Nemertea (proboscis worms)
Unique anterior proboscis surrounded by a fluid filled sac; alimentary canal; closed circulatory system
Mollusca (clams, snails, squids)
Coelomates with three main body parts (muscular foot, visceral mass, mantle); coelom reduced; most have hard shell made of calcium carbonate
Annelida (segmented worms)
Coelomates with body wall and internal organs (except digestive tract) segmented
Nematoda (roundworms)
Cylindrical, unsegmented pseudocoelomates with tapered ends; no circulatory system
Anthropoda (crustaceans, insects, spiders)
Coelomates with segmented body, jointed appendages, and exoskeleton made of protein and chitin
Echnodermata (sea stars, sea urchins)
Coelomates with secondary radial anatomy (larvae bilateral; adults radial); unique water vascular system; endoskeleto
Chordata (lancelets, tunicates, vertebrates)
Coelomates with notochord; dorsal, hollow nerve cord; pharyngeal slits; muscular, post-anal tail
created by yours truly with info from the review book!

Thought this would be a good addition, seeing that we sort of skimmed over chordate evolution


There are a few different ways in which natural selection is expressed in a population
1. Directional selection is a type of natural selection in which individuals that express a certain trait are favored over those who do not. An example would be mice with darker colored fur being selected over those with lighter fur, leading to an increase in mice with dark fur in a population
2. Disruptive Selection is a type of selection that favors individuals with variants at polar ends of the spectrum. An example would be mice with very light fur and very dark fur being selected over mice with medium colored fur. This results in an increase in both darker and lighter colored mice, with medium colored mice populations decreasing.
3. Stabilizing selection is the last type of selection, in which organisms that do not fall on either end of a trait's spectrum are selected over the extremes. In this case, mice with medium fur would be selected over more light or dark mice, providing an increase in medium colored mice populations, and seeing a reduction in the number of lighter or darker colored mice.

Something that confused me was the difference between prezygotic and postzygotic barriers

A Prezygotic barrier is a barrier that prevents mating or hinders fertilization, and include
  • Habitat Isolation- although two species might live in the same area, the habitat prevents them from mating
  • Bahavioral- A species uses specific signs or signals to attract mates
  • Temporal- Species may breed at different time like the time of day, different seasons, or years
  • Mechanical- Species can't reproduce
  • Gametic- Even if the gametes of two species meet, they might be unable to form a zygote
A Postzygotic barrier prevents a fertilized egg from developing into a fertile adult, and include
  • Reduced hybrid viability- when a zygote is formed, the genetic incompatability may cause development to stop
  • Reduced hybrid fertility- even if two species produce an offspring to adulthood, reporductive isloation still occurs if the offspring can't reproduce (like a donkey)
  • Hybrid breakdown- two species may produce fertile hybrids, but when the hybrids mate, the offspring might be weak or sterile
-review book

I think this picture does a good job of illustrating the difference between Darwin's idea of gradualism and Gould's idea of punctuated equilibrium. Fossil records show that organisms evolve relatively quickly in short periods of time, separated by longer periods of little to no change.
external image Evolution-gradualism-3.gif


I always mixed up allopatric and sympatric speciation, but this picture provides a simple explanation. A is showing allopatric speciation, where there is a geographical barrier. In B, sympatric speciation, the change occurs while in the same area.
external image allopatric_vs_sympatric_specitation.jpg

Here's a power point on allopactric vs. sympatric speciation! I thought I could use the review and see what the difference is between the two.

Although classification is not a huge component of the AP test, you never know when part of an essay may be about it. It is important to just know the basics. The domains of bacteria and archara contain prokaryotic organisms, and eukarya contains eukaryotic organisms.


When I was writing the evolution essays last night, I realized that I did not remember all of the evidence for evolution. I feel that evolution is a topic that is often dismissed as easy, but it actually is somewhat complicated. Though it doesn't seem as though there are many evolution questions on the diagnostic tests, I thought the evidence was worthwhile to review.

Evidence for Evolution
  1. Direct Observations of Evolutionary Change: evolution of drug-resistant viruses and antibiotic-resistant bacteria
  2. Fossil Record: fossils show evolutionary changes that have occurred over time, and when new organisms originated
  3. Homology: characteristics in related species can have an underlying similarity even though they carry out different functions. Example of homologous structures: forelimbs of mammals
  4. Convergent Evolution: explains why distantly related species can resemble one another. 2 organisms develop ANALOGOUS structures: two different organisms end up with similar solutions to a similar problem. Example of analogous structures: the torpedo shapes of a penguin, dolphin & shark are a solution to moving quickly through an aqueous environment. These organisms are distantly related, and these structures evolved independently in each species to solve a similar problem faced.
Summarized from review book.

I think that someone has posted about this somewhere else, but it applies here too.
The Endosymbiotic theory:
-proposes that mitochondria and plastids(chloroplasts) were formerly small prokaryotes that began living within larger cells
Evidence for this includes:
- both organelles have enzymes and transprt sytems homologous to those found in the plasma membranes of living prokaryotes
-both replicate by a splitting process similar to prokaryotes
-both contain a single, circular DNA molecule, not associated with histone proteins
-both has their own ribosomes which can translate their DNA into proteins
(Prokaryotes are the earliest living organisms, eukaryotes appeared 2.1 billion years ago, multicellular eukaryotes evolved 1.2 billion years ago)

Ancestral vs. Derived characteristics -- Ancestral characteristics are characteristics that were present in an ancestral species while derived characteristics were not. Below is a picture that describes / shows the difference

Advantages of phylogenetic classification
Phylogenetic classification has two main advantages over the Linnaean system. First, phylogenetic classification tells you something important about the organism: its evolutionary history. Second, phylogenetic classification does not attempt to "rank" organisms. Linnaean classification "ranks" groups of organisms artificially into kingdoms, phyla, orders, etc. This can be misleading as it seems to suggest that different groupings with the same rank are equivalent. For example, the cats (Felidae) and the orchids (Orchidaceae) are both family level groups in Linnaean classification. However, the two groups are not comparable:
  • One has a longer history than the other. The first representatives of the cat family Felidae probably lived about 30 million years ago, while the first orchids may have lived more than 100 million years ago.
  • The have different levels of diversity. There are about 35 cat species and 20,000 orchid species.
  • They have different degrees of biological differentiation. Many orchids belonging to different genera are able tohybridize. But the same is not true of cats — house cats (belonging to the genus Felis) and lions (belonging to the genus Panthera) cannot form hybrids.
Orchids of these two different genera hybridize...
external image dot_clear.gif
...but cats of these two different genera do not.
Laelia purpurata
Laelia purpurata

crosses with
crosses with

Cattleya mossiae
Cattleya mossiae

House cat
House cat

external image nothybridize.gif



There is just no reason to think that any two identically ranked groups are comparable and by suggesting that they are, the Linnaean system is misleading. So it seems that there are many good reasons to switch to phylogenetic classification. However, organisms have been named using the Linnaean system for many hundreds of years. How are biologists making the transition to phylogenetic classification?

This website has an interactive video thing of the Miller and URey experiment testing the hypothesis or Oparin and Haldane.
In summary: Oparin and Haldane hypothesized that the early atmosphere was thick with water vapor, nitrogen, carbon dioxide methane, ammonia, hydrogen, and hydrogen sulfide. This combination provided with energy from lightning and UV radiation could have formed organic compounds, a primitive "soup" from which life arose.
The experiment itself was done in a jar with such gases and an electrical charge imitating the lightning and produced a variety of amino acids which are building blocks. This is a picture of the overall experiment, more information on this link
external image Origin1.jpg

Fossils are evidence that evolution is occurring or has occurred.
The Fossil Record

illustration of geological strata containing an evolutionary sequence of fossils from 570 to 2 million years ago
illustration of geological strata containing an evolutionary sequence of fossils from 570 to 2 million years ago

Geological strata containing an
evolutionary sequence of fossils
Remains of animals and plants found in sedimentary rock deposits give us an indisputable record of past changes through vast periods of time. This evidence attests to the fact that there has been a tremendous variety of living things. Some extinct species had traits that were transitional between major groups of organisms. Their existence confirms that species are not fixed but can evolve into other species over time.
The evidence also shows that what have appeared to be gaps in the fossil record are due to incomplete data collection. The more that we learn about the evolution of specific species lines, the more that these so-called gaps or "missing links in the chain of evolution" are filled with transitional fossil specimens. One of the first of these gaps to be filled was between small bipedal dinosaurs and birds. Just two years after Darwin published On the Origin of Species, a 150-145 million year old fossil of Archaeopteryx was found in southern Germany. It had jaws with teeth and a long bony tail like dinosaurs, broad wings and feathers like birds, and skeletal features of both. This discovery verified the assumption that birds had reptilian ancestors.

external image Archaeoptryx_1.jpg

external image Archaeoptryx_2.jpg

external image Archaeoptryx_3.gif
Archaeopteryx fossil

Archaeopteryx recreation

Archaeopteryx tail feathers
Since the discovery of Archaeopteryx, there have been many other crucial evolutionary gaps filled in the fossil record. Perhaps, the most important one, from our human perspective, was that between apes and our own species. Since the 1920's, there have been literally hundreds of well-dated intermediate fossils found in Africa that were transitional species leading from apes to humans over the last 6-7 million years. This evidence is presented in the last 3 tutorials of this series.

The fossil record also provides abundant evidence that the complex animals and plants of today were preceded by earlier simple ones. In addition, it shows that multicelled organisms evolved only after the first single-celled ones. This fits the predictions of evolutionary theory.


On the Biology SAT 2's I had a few questions about taxonomy that got me a little confused
Taxonomy is the ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences.
external image widget_akvPeY8m1gMB0GkMGFrybH.jpg
This image really helped me to review the order of descent of taxonomy, and the book provided me with a mnemonic device just in case. King Phillip climbed over the fence and got shot. Hope this helps if anyone else gets confused with it.

When trying to understand pedigree charts, I always get confused on what the different symbols mean towards the individual. This chart gives a clear explanation for what each symbol means. I also attached a diagram of a basic pedigree chart.
external image pedigreeSymbols.jpg
external image pedigree1.gif

I don't think we've reviewed asexual reproduction for a long time. Here is a refresher
Some forms of asexual reproduction are budding, internal buds, fragmentation, regeneration, and parthenogenesis

One of the topics I have the most trouble with is categorizing animals into the different phylum. This chart shows the differences between protostomes and deuterstomes.

A) Cleavage- In general, protostome development begins with spiral, determinate cleavage. Deuterostome development is characterized by radial, indeterminate cleavage
B) Coelom formation- coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm. In the deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron.
C) Fate of the blastospore- in protostome development, the mouth forms from the blastospore. In deuterostome development, the mouth forms from a secondary opening

A few times in our evolution unit, Hox genes came into discussion. I never knew what those were or why they were significant, so I thought I would make a post about it. Hoxgenes are a group of regulatory genes that control the timing and route of development and contribute to body segmentation. This information might me extraneous, but it is extremely interesting, and if you happen to have an essay about evidence for evolution I bet it would be impressibe to mention these genes! Also, this essay does an excellent job with simplifying and clarifying the information, so definitely check it out:
Also, this picture is a good representation of Hox genes. It shows how similar genes control the segmentation of different organisms and end up with different products, like a human torso and fly wings.

I believe that these terms are extremely important to know, as they are mainframe vocabulary for the section.
Here are the key terms of evolution in summary.
You can quiz yourself on the below listed terms and play games with the terms at:
QuizLet Evolution Review

Happy Studying!
external image spacer.MzUH.gifEvolution
external image spacer.MzUH.gifall of the changes that have transformed life over an immense time.
external image spacer.MzUH.gifAdaption
external image spacer.MzUH.gifan inherited characteristic that improves an organisms ability to survive and reproduce in a particular
external image spacer.MzUH.gifBeagle
external image spacer.MzUH.gifthe name of the ship that Charles Darwin sailed on in the 1830's
external image spacer.MzUH.gifDescent With Modification
external image spacer.MzUH.gifthe theory of Darwin that all of the species living on earth today descended from earlier species.
external image spacer.MzUH.gifNatural Selection
external image spacer.MzUH.gifthe process by which individuals with inherited characteristics well suited to the environment leave more offspring on average than do other individuals.
external image spacer.MzUH.gifFossils
external image spacer.MzUH.gifpreserved remains of organisms that lived in the past
external image spacer.MzUH.gifFossil Record
external image spacer.MzUH.gifthe collection of fossils recorded in rock layers over time
external image spacer.MzUH.gifExtinct
external image spacer.MzUH.gifspecies that no longer exist
external image spacer.MzUH.gifHomologous Stucture
external image spacer.MzUH.gifsimilar structures among related species
external image spacer.MzUH.gifVestigial Structure
external image spacer.MzUH.gifhomologous structures that have a major function in one species but not in a related species
external image spacer.MzUH.gifPopulation
external image spacer.MzUH.gifA group of individuals of the same species living in a particular area at the same time
external image spacer.MzUH.gifVariation
external image spacer.MzUH.gifdifferences among members of the same species
external image spacer.MzUH.gifArtificial Selection
external image spacer.MzUH.gifselective breeding of plants and animals to produce offspring with traits that humans value
external image spacer.MzUH.gifGene Pool
external image spacer.MzUH.gifconsists of all the alleles [different forms of genes] in all the individuals of a population
external image spacer.MzUH.gifMicroevolution
external image spacer.MzUH.gifa generation-to-generation change in the frequencies of alleles withen a population
external image spacer.MzUH.gifHardy Weinberg Equilibrium
external image spacer.MzUH.gifpopulations that do not undergo change to their gene pools[not evolving]
external image spacer.MzUH.gifGenetic Drift
external image spacer.MzUH.gifchange in a gene pool due to chance
external image spacer.MzUH.gifGene Flow
external image spacer.MzUH.gifthe exchange of genes with another population
external image spacer.MzUH.gifFitness
external image spacer.MzUH.gifthe contribution an individual makes to the gene pool of the next generation compared to the contribution of other individuals