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Presentation Details: Slides: 7 Duration: 00:04:08 Filename: C:\Users\jpage\Documents\NCVPS Learning Objects\Biology\Biology Trees & Keys Navigation to PPT W\Trees & Keys\keys & trees lo2.ppt Presenter Details: What are Dichotomous Keys? a method for determining the identity of something (like the name of a butterfly, a plant, a lichen, or a rock) by going through a series of choices that leads the user to the correct name of the item. A dichotomous key is a listing of characteristics, such as structure and behavior, organized in such a way that an organism can be identified or classified. Think of a dichotomous key as a type of scavenger hunt. Dichotomous means "divided in two parts". Published by Articulate® Presenter www.articulate.com Slide 1 What are Dichotomous Keys? What are Dichotomous Keys? Duration: 00:00:36 Advance mode: Auto a method for determining the identity of something (like the name of a butterfly, a plant, a lichen, or a rock) by going through a series of choices that leads the user to the correct name of the item. A dichotomous key is a listing of characteristics, such as structure and behavior, organized in such a way that an organism can be identified or classified. Think of a dichotomous key as a type of scavenger hunt. Dichotomous means "divided in two parts". Notes: What are dichotomous Keys? These keys are a method for determining the identity of something like the name of a butterfly, a plant, or a rock. This is accomplished going through a series of choices that leads the user to the correct name of the item. A dichotomous key is a listing of characteristics, such as structure and behavior, organized in such a way that an organism can be identified or classified. Think of a dichotomous key as a type of scavenger hunt. Dichotomous means "divided in two parts". Slide 2 Using a dichotomous key Duration: 00:00:39 Advance mode: Auto Using a dichotomous key At each step of the process of using the key, the user is given two choices; each alternative leads to another question until the item is identified. 1a. If the leaves are flat….go to question 4. 1b. If the leaves are needle-like….go to question 2. 2a. Are the needles in a bunch? Go to question 5 2b. Are they spread along the branch?“…pine tree Eventually, when enough questions have been answered, the identity of the tree is revealed. Published by Articulate® Presenter Notes: Using a dichotomous key At each step of the process of using the key, the user is given two choices; each alternative leads to another question until the item is identified. For example 1a. If the leaves are flat….go to question 4. 1b. If the leaves are needle-like….go to question 2. 2a. Are the needles in a bunch? Go to question 5 2b. Are they spread along the branch?“…pine tree Eventually, when enough questions have been answered, the identity of the tree is revealed. www.articulate.com Slide 3 Dichotomous Key Example Duration: 00:01:06 Advance mode: Auto DICHOTOMOUS KEY EXAMPLE 1. a. tail fins are horizontal—whale………………….go to 2 b. tail fins are vertical—fish……………………….go to 3 2. a. has teeth or tusk—toothed whale………………..go to 4 b. has no teeth………………………...BALEEN WHALE 3. a. has gill slits behind mouth—shark…….………...go to 5 b. has no gill slits……………………..NONSHARK FISH 4. a. black with white underside………….KILLER WHALE b. tusk, gray with dark spots………………....NARWHAL 5. a. head is hammershaped……..HAMMERHEAD SHARK b. tail is half the body length……….THRESHER SHARK Notes: Look at this key to figure out the name of the whale below. You probably already know this is a killer whale. But lets use the key to confirm that this is a killer whale. We need to start at the top. Number 1. Every time you use a key you ALWAYS start at the top. Ok so when we look at the key we see we have 2 choices. a. tail fins are horizontal—whale………………….go to 2 or b. tail fins are vertical— fish……………………….go to 3. Being that the fins are on the horizontal we know this is a whale and we need to go to number 2. Now lets look at number 2. We have to chose from 2 statements. a. has teeth or tusk—toothed whale………………..go to 4 or b. has no teeth………………………...BALEEN WHALE Being this whale has teeth we are going to go to 4. Now lets look at 4. Again we have 2 choices. a. black with white underside………….KILLER WHALE OR b. tusk, gray with dark spots………………....NARWHAL Being that this whale is black with a white underside we know it is a killer whale. Published by Articulate® Presenter www.articulate.com Slide 4 Reading phylogenetic trees Reading phylogenetic trees Notes: Another tool scientist use are called Phylogenic trees. A phylogeny, or evolutionary tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa that are believed to have a common ancestor. Duration: 00:00:19 Advance mode: Auto A phylogeny, or evolutionary tree, represents the evolutionary relationships among a set of organisms or groups of organisms, called taxa (singular: taxon) that are believed to have a common ancestor. Slide 5 Tips, Internal Nodes, Edges Tips, Internal Nodes, Edges Duration: 00:00:31 Advance mode: Auto The tips of the phylogenetic tree represent groups of descendent taxa (often species) The internal nodes of the tree represent the common ancestors of those descendents. The tips are the present and the internal nodes are the past. The edge lengths in some trees correspond to time estimates – Notes: Lets look at how to read one of these keys. The tips of the phylogenetic tree represent groups of descendent taxa (often species) The internal nodes of the tree represent the common ancestors of those descendents. The tips are the present and the internal nodes are the past. The edge lengths in some trees correspond to time estimates – evolutionary time. evolutionary time. Slide 6 Sister Groups and a common ancestor Duration: 00:00:35 Advance mode: Auto Notes: From these trees we can see sister groups and which organisms have a common ancestor. Two descendents that split from the same node are called sister groups. In the trees above, species A & B are sister groups — they are each other's closest relatives; which means that they have a lot of evolutionary history in common and very little evolutionary history that is unique to either one of the two sister species and that they have a common ancestor that is unique to them. Published by Articulate® Presenter www.articulate.com Slide 7 Equivalent trees Duration: 00:00:22 Advance mode: Auto Published by Articulate® Presenter Notes: There are places on the tree where organisms are equivalent. For any speciation event on a tree , the choice of which lineage goes to the right and which one goes to the left is arbitrary. These three phylogenies are therefore equivalent. www.articulate.com