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Current time:0:00Total duration:6:05

Molecular evidence for evolutionary relationships examples

AP.BIO:
EVO‑1 (EU)
,
EVO‑1.M (LO)
,
EVO‑1.M.1 (EK)
,
EVO‑1.N (LO)
,
EVO‑1.N.2 (EK)

Video transcript

an investigation was carried out on four different plant species to determine which of three species was most closely related to an unknown plant species the results of the investigation are shown in the data table below which plant species appears to be most closely related to the unknown species support your answer so pause this video and see if you can figure that out alright so here in this data the first row is for our unknown species we know that it tests positive for enzyme M this is blanked out because this is says how many differences in amino acid sequences are there between the species in that row and the unknown species and of course the unknown species would have zero differences because it is itself and then this is the gel electrophoresis banding pattern so what we want to do is look for as many similarities as possible to our unknown plant species so first if we looked at the enzyme whether we test positive for it species one does not test positive for its species two and three do so species one is not looking good if we look at differences in amino acid sequences species one once again has the most differences in amino acid sequences so that confirms our belief that it might be the most different from plant from the unknown plant species but then if we look between plant species two and three plant species two has fewer differences so right now plant species two is looking like the leading candidate plant species three has more differences and then when we look at the gel electrophoresis banding pattern plant species two has the exact same pattern as our unknown plant it's the only one with the exact same pattern and so because of that I'm feeling really good saying that two is most closely related to the unknown species two because same banding pattern banding pattern and we could say and least different least different amino acid sequences amino acid sequences and test positive for enzyme M tests positive for enzyme enzyme M let's do another question like this scientists attempted to determine the evolutionary relationships between three different finch species a B and C in order to do this they examined the physical characteristics and DNA of these species DNA was extracted from all three species and analyzed using gel electrophoresis the results are shown in the diagram and then they asked us which statement best describes the method used above to determine the evolutionary relationships between three species of finches so the first choice is examine the structure of the beaks and compare them statement to observed behavioral and physical characteristics of all the finches and group them by similarities C obtained molecular evidence from all three species and identify similarities for compare common ancestors of all three of the species and see if they are the same so pause this video and see which choice you like alright well clearly they're looking at molecular evidence they're taking the DNA of the different species they're amplifying them which means they're making a bunch of copies of certain sequences of that DNA and then they're running a gel which means they allow those different segments to separate on this gel the smaller segments are going to migrate down further the larger segments are going to migrate less far and the more similarities you have on this gel electrophoresis right over here this banding pattern the more similarity the more similar that DNA probably is and so they are definitely using molecular evidence and three is the only one that talks about molecular evidence so I will go with choice three they did say in the beginning that they're looking that they examined physical characteristics and DNA of these species and so you could maybe say examine the structure of the beaks and compare them but that's very specific and it didn't say for sure that they're doing that that that may be one of the physical characteristics that they're looking at but we know for sure that they are obtaining molecular evidence from all three species and they're identifying the similarities so now this next part it says based on the data they collected using gel electrophoresis label the branching tree diagram below writing the letters a B and C to represent the possible evolutionary relationships between species a b and c so pause this video and see if you can figure this out and I'll look at I'll show you the banding pattern again alright so down there and actually I'll redraw it up here they draw a tree that looks like this and they want us to put A's B's and C's in these blanks here and one way to think about it is these two are more closely related they have a more a more recent common ancestor than the then from this one over here so if we look at the banding patterns it's pretty clear we have this similar band on a and B we have this similar band on a and B and they have this band right over here in common although C shares that one as well the only other band that a shares in common with C is this one right over here and B doesn't share anything else in common with C so it's pretty cut it's pretty clear that a and B share the most common banding patterns so I would write that a and B have the most recent common ancestor and that C is more distant
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