Tree of life: Vegetarian edition: We often use the terms fruit and vegetable to describe the plants we eat; however, not many people know the real difference between them. If you’re a botanist, a fruit isn’t something sweet and delicious—it’s the part of some plants that contains the seeds. This makes things like tomatoes, nuts, and squash fruits, technically! Any other part of a plant that we eat is called a vegetable. Some vegetables are roots, like carrots, and others are stems or leaves, like celery and lettuces. Being an animal yourself, it’s often easy to overlook plants and their many interesting traits. In this level, you’ll gain a new appreciation for some of the plants we eat. Things are getting more challenging now, so be sure to use the species and species compare tabs! Answer the next 2 questions before you move on to Mission 2, “Fossils—Rocking the Earth.”  What makes seaweed different from all the other plants on the Tree of life: Vegetarian edition? 

Which do you consider more convincing evidence, DNA or physical features? Why?

Fossils almost never contain DNA. So how can we know how closely or distantly related fossil organisms are to living organisms?

Origin of whales: In the previous level, you looked at the transition from water to land and the evolution of tetrapods. Several groups of tetrapods went on to make the reverse trip—they headed back to the water.  In this level, you’ll put together a tree that summarizes some of the changes that occurred as a group of mammals, closely related to the modern-day hippopotamus, returned to the sea. Answer the 3 questions below before you move on to Mission 3, “DNA Spells Evolution.”  When did whale ancestors begin living full time in the water?

We know that Tiktaalik is more closely related to Acanthostega than it is to Eusthenopteron because Tiktaalik and Acanthostega:

Frog legs and fish eggs: When scientists compare DNA, there are usually thousands upon thousands—or even millions—of nucleotide bases involved. A computer then scans the sequences and aligns them in the way that provides the best match. In some cases, the computer will add “blank” spaces to improve alignment. Such spaces represent nucleotides that were added or deleted as opposed to changed in one or more lineages. In this level, you’ll get the hang of analyzing DNA by looking at a tiny 4-base snippet. A dash (–) represents either a blank space added to improve alignment or a position that is not important for the analysis you’ve been asked to do. To make things easier, the information from the species compare tab is shown below. However, don’t forget to read the species tabs—they might help you.  If we put the information we have into a tree, it might look like this:  True or False: “The change from a C to a T at position 1 caused all of the changes that exist between the cichlid and coelacanth/frog.”

Which biological trait could fit in the “trait” spot on this tree? 

A clade is a fancy word for any group in a phylogenetic tree that includes an ancestor and all of its descendants. A simplified dinosaur tree is included below. Imagine that you have a pair of scissors and can cut the tree. You can tell a group is a clade because it would only take one “snip” to make the group “fall off” the tree.  Five different clades have been marked on the tree with brackets. The clade marked 1 is clade Aves—the birds. The clade marked 2 is clade Theropoda—the theropods. Clades 2 and 3 are the two major groups of dinosaurs—clade Saurischia and clade Ornithischia. Finally, clade 5 is clade Dinosauria—the dinosaurs. The version of the diagram below shows where you can “snip” off each clade. For example, clade 4 can be “snipped” where the 4 is written.  If we look at where Triceratops is on the tree, it belongs to two of the marked clades: 4 and 5. This means that Triceratops is both an ornithischian (clade 4) and a dinosaur (clade 5). If we do the same for birds, we can see that they belong to clades 1, 2, 3, and 5 by moving down the tree.  Given this information, why are birds dinosaurs? 

Which lived more recently in time: the common ancestor species of A and B or the common ancestor species of B and C?

Using tree from previous question, Which trait(s) do B and C share?