okay so this is part two to my ap bio phylogenetics uh videos and so uh in this little short video we're gonna talk about how do you actually like draw a phylogenetic tree well or cladogram right so when we look at our sources of data like what information do we use to draw trees well we're going to use morphological which is looking at different shapes or structures so that could be like actual living species we can like study their characteristics and what they have in common um or it can be through the fossil record for like the structure of fossils biochemical would be things like um metabolic pathways that are present or absent in organisms you have your molecular data which your molecular data is going to be like dna sequence or amino acid sequence which really is going to be the most accurate and the most reliable data so if given a like a choice you're going to want to use dna sequence or amino acid sequence or the differences in amino acids or the differences in nucleotides between species to determine their evolutionary relatedness now behavioral data can also be used as well now i do want to point out when we talk about morphological data why morphological data is something you should be careful of is because of convergent evolution in a couple of my videos i have talked about the marsupial animals in australia and placental mammals in north america now if they've evolved through convergent evolution to look very similar if you're studying their fossils um you may not know just based on morphology how truly distantly related they are right so that is where more uh molecular data would be better because convergent evolution can be a bit misleading on evolutionary relationships okay so let's go ahead and see how we do this so i have my four little made up organisms that i drew and what we see here is we're going to look at morphological data and what we see is a character table so the way we fill in a character table is i look at my organisms and i see that all four of the species have six legs so in the character table i'm gonna put a plus sign for every species that has that trait now i notice in my species number one though that number species number one does not have blue spots antennae or wings so for that uh species one gets like a little wine like a minus symbol right but the other three species all have blue spots then i look at antenna species one does not have antenna uh species two does but species 3 doesn't and 4 does then i look at wings and really that's only going to be in species 4. so here i have traits that are present in the different species and traits that are absent so now we can use those uh characters or traits to draw the evolutionary relationship so i'm going to start with like a cladogram style a drawing so here i see that all four species have six legs so that is like a shared ancestral trait that was in the ancestor of all four species but if i look at species number one species number one doesn't have any other traits in common with the remaining three so therefore after six legs evolved in an ancestor there was a divergent like event right divergent evolution so species one um like diverged from the other three species way far back in time because there's nothing else in common with the rest of them then i look at um blue spots so the remaining three species all have blue spots so on this line right here this is like a shared evolutionary past so blue spots a rose and an ancestor to species two three and four it is a shared derived trait in those three species however when i look at species number two i'm sorry species number three it doesn't have anything else in common with species two or four it really only has those six legs and blue spots so there's a divergent uh a speciation event basically is what has happened here then we have um antenna is next that's in species two and four but then i noticed that species four is the only one with wings now i just realized as i was talking that i didn't include this here i have traits that are all um like have all shown up in a species now you could also have a traits that are lost evolutionarily like we see in snakes for example like snakes and lizards do share a recent common ancestor however in snakes their ancestor actually had legs and their legs were selected against so if you look at snake evolution you can see still see today the vestigial structures for a pelvic bone so through the fossil record we can see how limbs have been lost in snakes and so it's not always gaining traits you can also lose traits evolutionarily like there's in my video on um evidence for evolution i use the example of a blind cave fish so there's a fish today who has an eye socket but doesn't have an eye like that would be a trait that has been lost but it's ancestor head eyes okay and now some people prefer to draw or sometimes you see the phylogenetic trees drawn in this style so this would be how you draw it um in this like shape or style a phylogenetic tree so they both show the same thing now i do want to point out though these highlighted yellow parts these traits represent shared drive traits which basically indicate common ancestry and it helps you draw your hypothesis of how these species evolved throughout time remember these trees are not just but they are a hypothesis or hypotheses and they are um like able to be reconstructed or re-evaluated as we gather more evidence maybe new fossils are discovered a new technology is developed and we're able to refine these hypotheses and redraw them that is totally possible science is wonderful because it can change as we uh deepen our understanding now i also want to point out though this species number one we notice it doesn't have much in common with the others so we call this species number one an out group an l group is a lineage that is the least closely related to the remainder of the organisms in the phylogenetic tree or the cladogram so one would be our out group and then three two and four would be what we call like an in group and they have like shared derived characters and we can see how uh their evolutionary path basically okay and so our last thing to look at in this video is how do we use molecular data like i mentioned earlier is one of the best sources of evidence or data to use when constructing a tree or cladogram so in molecular data that can be either like in this example here i have the number of amino acid differences now if we remember our dna sequence is what codes for codons which then codes for amino acids and then that forms apply peptide so here we have protein x that's made of however many amino acids and if we have like a missense mutation in an exon that'll change the amino acid but the protein may still be built so that is um what we're looking at now if it's a silent mutation then we really wouldn't see any amino acid differences you'd only be able to tell silent mutations if you were looking at the actual dna sequence okay so let's go ahead and see how we fill in a table like this though so species a we're going to compare the two species so we're looking at like the number of differences between species a and species b between species a and species c etc so if i were to compare the number of amino acid differences in protein x between species a and species a you would expect to not find any differences because they're the same species so in a chart like this or a table like this we put just like a dashed line or like a zero like there's no differences because they're the same species however if i wanted to compare species a to species b i see here there's four amino acid differences um in their protein x now if i want to compare species a to c there's two differences if i compare species a to d there's six and a to e there's ten differences so if i look at just this row to me what i interpret is that species a and c have a recent common ancestor there's very little differences between them whereas species a and e are more distantly related their common ancestor is further back in time they've been separated for longer because we have these things called molecular clops and molecular clocks are basically like the rate of mutations the rate of mutation is pretty constant across species so you can kind of gauge how long two species have been separated evolutionarily based on the number of mutations that have shown up in their two lineages okay now let's go ahead and compare species b to b and this oh i'm sorry here if i compare b to a we already did that it was four so we don't do it again uh we can either do a dashed line or we can just shade it in or leave it blank and now for b to b again we're going to expect no differences and then we fill in the rest oh that one right there is pretty important you always want to look for the numbers that are the smallest which implies very closely related a very recent common ancestor as well as the numbers that are the most different that also is going to tell you about your out group now species um a and c we know had two differences species c and b we know we had six differences so now we're at c to c and it's like they're the same species then we have five and nine and then we continue filling in this table now what do we do with this table though right like how do we use this to draw our trees so let's go ahead and check that out so here i have the table and what i like to do is i like to start with the ones that are most closely related so what i see here oh i also look for my out group which one is the most different is also very important so here i have e is my out group and then i notice that b and d have only one difference so they have a very recent common ancestor then a and c also have a very recent common ancestor and if you're looking at this you might be thinking well that's not a cladogram or a phylogenetic tree but for me i find it really easy then just to connect the lines basically so now i have a tree and if you like check the numbers and data it really does work out now we also want to point out that these trees can be switched at the nodes it would need the same thing now we can also draw our tree uh this way i'm sorry so we can switch it at the nodes all right means the same thing now if i look at the like goal post style uh here b and d had only one amino acid difference so they have a pretty recent common ancestor and then we had a and c they had two differences so i drew their line their more recent common ancestor a little bit further back in time if you remember from my last video phylogenetic trees are kind of like calibrated based on molecular clocks like the rate of mutations and how many differences there are now uh e was our out group so that's a further back so this is how i would draw uh this this table in a phylogenetic tree style all right right so that's it i think at this point if you're in a biology class i'm guessing your teacher's next step is to now practice with different character tables and molecular data tables for you to draw your own trees alright alright great job