Investigation of the Evolution of Vertebrate Diversity

Backgroundbased on Chapter 19

Scientists have identified more than 1.3 million species of animals. Classifying animals isn’t always easy. Think of a platypus, which is native to Australia. It has a bill and webbed feet like a duck, but fur on the rest of its body like a mammal. It lays eggs like a bird, but produces milk to feed its young like a mammal. Is this animal a bird or a mammal? It is a mammal because it has and produces milk.

The incredible diversity of animal life arose through hundreds of millions of years of evolution, as natural selection shaped adaptations to the Earth’s diverse and changing environments. With so much diversity, it may be difficult to determine how organisms are related together. Remember, all animals will have a common ancestor of the past.

When Darwin created his theory of evolution, he used samples collected from the Galapagos Islands. He shared his findings in his book, On the Origin of Species. Today, we can use scientific technologies to examine the relationships among species. This method is similar to those used to determine family relationships or ancestral background in humans.

In this investigation, we will study the evolutionary history of different vertebrate animals. We will use gel electrophoresis to study the organisms’ biological molecules. Gel electrophoresis uses agarose gels to separates macromolecules according to their size and charge. Samples are loaded into the agarose gel which is then placed into a chamber with electrodes at each end. The biological molecule will travel towards the + electrode. An electrical current is applied to the gel and cause the molecules to move. Animals with similar patterns will be more closely related.

Pre-Investigation Questions

  1. Why is there so much diversity in the animal kingdom?
  1. Draw a possible sample gel electrophoresis between a dog, crow, and platypus?
  1. What does gel electrophoresis separate?

Vertebrate Evolution from Annenberg Learner

All vertebrates have a nerve cord that runs along the length of their back. It may be enclosed as a backbone or not. Within the group of vertebrates, there has been a large amount of evolution to adapt to the many diverse habitats.

Jaws: The earliest vertebrates in evolutionary history are the fish. The earliest fish had no jaws. They sucked and rasped flesh of their prey rather than biting it. Fish that arose later have jaws. Jaws represent a much more efficient and effective mode of capturing, feeding on, and swallowing prey.

Lungs and limbs: In order for vertebrates to succeed on land, they had to be able to breathe and move around.

Watertight skin and eggs: To live exclusively on land requires the ability to avoid water loss. The next adaptations in vertebrate evolution included skin that acts as a watertight barrier.

Endotherm: This is what we typically call “warm-bloodedness.” This occurs as body temperature is regulated internally using heat supplied by the burning of food for fuel.

Number the animals below in the order you believed they evolved.

Materials

  • Premade gel
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  • Gel casting tray
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  • 300 mL diluted electrophoresis buffer

  • Pipettes
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  • DNA samples
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  • Electrophoresis chamber

  • Power source
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  • Gloves
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  • Goggles

Procedure

Loading the Samples

  1. Obtain a prepared agarose gel from your teacher.
  2. Place the gel (on its bed) into the electrophoresis chamber, properly oriented, centered and level on the platform.

The wells should be at the (-) end of the box where the black lead is connected.

  1. Fill the electrophoresis apparatus chamber with 300 mL of diluted electrophoresis buffer solution.
  2. A small amount of sample will cling to the walls of the tubes. Tap the top of samples, so itfall to the bottom of the tubes.
  3. Using a plastic pipette, pierce the foil top of tube A with the tip and withdraw the sample.
  4. Load the sample into Lane 1 well of the gel.

Designate Lane 1 as the left most lane of your gel.

Be careful not to poke a hole in your gel by inserting the pipette too far into the well.

  1. Repeat step #5-6 with a new pipette for tubes B-E.

Lane # / Tube / Animal Sample / Color
1 / A / Lungfish / Blue
2 / B / Monitor / Red
3 / C / Panda / Yellow
4 / D / Tree Frog / Purple
5 / E / Parrott / Orange

Running the Gel

  1. Place the lid on the electrophoresis chamber – it will only attach in 1 way.
  2. Insert the plug of the black wire into the black input of the power source (negative input). Insert the plug of the red wire into the red input of the power source (positive input).
  3. Set and turn on the power supply to 120 V for at least 15 minutes.
  4. After the electrophoresis is completed, turn off the power, unplug the power source, disconnect the leads and remove the cover.
  5. Carefully remove the gel and tray from the box.

The gel will be very slippery!

  1. Record your results.
  2. Clean up.

Wash and dry the materials.

Put materials back to original place.

Data & Analysis

Record your data as seen in your completed gel below. (*Make sure to label the lanes/samples!)

  1. Which band do you believe is in the most evolved animal? Which animal do you think it represents?
  1. Which band do you believe is the least evolved animal? Which animal do you think it represents?
  1. Which other animal is most closely related to the most evolved animal?
  1. Which other animal is most closely related to the least evolved animal?
  1. Which animal is the “middle” evolved animal?

Share Results – Create a Cladogram

A cladogram or clade is a diagram used to represent a group of species that includes an ancestral species and all its descendants.

Create a cladogram based on your results. Label the defining feature (listed under “Vertebrate Evolution”) that caused the separation from the common ancestor.

Conclusion _____Reflect on your initial thoughts when you numbered the organisms in order of least to most evolved. ____Discuss how your claim changed with the addition of new data. ____Also reflect on how this investigation shows evolution.

______