Join Melanie on a 5K in episode 73. Phylogeny studies the evolutionary history amongst groups of organisms. It tells the story of relatedness, the branches in the road.
Join Melanie on a 5K in episode 73. Phylogeny studies the evolutionary history amongst groups of organisms. It tells the story of relatedness, the branches in the road. (1:37). Be careful - just because two organisms are physically adjacent on a diagram, does not mean they are more closely related (4:05). The episode concludes with unit connections and exam tips (5:34).
The Question of the Day asks (6:50) Ernst Haeckel coined the phrase “ontogeny recapitulates phylogeny.” What is ontogeny?
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Hi and welcome to the APsolute Recap: Biology Edition. Today’s episode will recap Phylogeny
Zoom out:
Unit 7 - Natural Selection
Topic 7.9
Big idea - Evolution
Imagine you and a friend are running a 5K. This particular race has several different pathways you can take, all with checkpoints. As a runner, you get your hand stamped every time you pass a checkpoint - maybe with a star, smiley face, lightning bolt - you get the picture. The starting pistol sounds and you are off, branching left where your friend branches right. Who took the better path? Only time will tell.
Let’s Zoom in:
You and your friend meet up in the parking lot after the race to compare stamps. You each have a star, but you have a smiley face and she has a lightning bolt. From this data, you conclude that you must have passed at least one of the same checkpoints along your path. Your friend describes a really rocky terrain whereas yours was smooth but hilly. Neither path was better, just different and each was exactly 5 kilometers in length. (RECORD SCRATCH). What in the world does this have to do with evolution?
Phylogeny studies the evolutionary history amongst groups of organisms. It tells the story of relatedness, the branches in the road, and the traits (or stamps) accumulated or lost along the way. Much like the 5k, organisms can start at the same evolutionary marker and diverge along different paths. And with this information, we construct phylogenetic trees! But how do we know which organisms are related?
Oftentimes, character tables are used to construct phylogenetic trees or branching diagrams. Characteristics, like the vertebral column, might separate the outgroup of lancelets from other vertebrates whereas a hinged jaw excludes the lamprey. It should be noted that a diagram can only infer relatedness based upon available data (organisms, characteristics) to the specific example at hand. Add in a new organism or another characteristic, and the phylogenetic tree would likely be modified. For this reason, phylogenetic trees represent hypotheses and are continuously being revised. Molecular data (like DNA and protein similarities - cytochrome C sound familiar?) provides more reliable and accurate evidence than physical similarities (living or fossil evidence) when constructing phylogenetic trees.
You will be expected to explain how a phylogenetic tree can be used to infer evolutionary relatedness. Phylogenetic trees show ancestral relationships, with the branching point or node of separation representing the most recent common ancestor. Organisms adjacent and connected to the same node are often called sister taxa. DO NOT FALL IN THIS TRAP. Just because two organisms are physically adjacent on a diagram, does not mean they are more closely related. Follow the lines back to a node - where two connect, you have a common ancestor, shared derived characteristics, and relatedness. Imagine that this node is a pivot point, which can swivel and cause the organisms on top of it to swap places. For this reason, if organism A and B are connected to a node together, and going further back they are connected to organism C - I cannot say that B is more closely related to C than A is. Even if it is physically adjacent on the diagram labels. The node could swivel, causing A to be physically closer to C, which is more of a diagraming/labeling personal preference, and not a hint at evolutionary relationships. What I can conclude is that speciation has occurred, with A, B, and C each on separate paths.
Time for unit connections. Small connection unit 5 - heredity and Unit 1 - the chemistry of life. The more related two species are, the greater their molecular overlap should be. Alright - what about the exam? Make them, use them, interpret them - get cozy with phylogenetic trees. Study them from all angles with the ancestral root organism facing left, right, down and up. And don’t just look at animal examples - there are three whole domains to pay attention to. When the AP Bio curriculum went through revision for 2020 exams, many people were upset - ok well lets say many teachers were upset - that alot of biodiversity and body systems were removed. But remember, the college board can ask you about anything if they give you enough background information. Phylogenetic analysis is a great example of that.
To recap……
Phylogenetic trees show the evolutionary relatedness between organisms. Constructed from molecular and morphological data, organisms are placed on branches connected by nodes. Organisms are more closely related if they share a recent common ancestor.
Coming up next on the Apsolute RecAP Biology Edition: Common Ancestry
Today’s question of the day is about change.
Question of the day: Ernst Haeckel coined the phrase “ontogeny recapitulates phylogeny.” What is ontogeny?