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Biology library
Course: Biology library > Unit 26
Lesson 1: Evidence of evolution- Biodiversity and natural selection
- Evidence for evolution
- Fossils: Rocking the Earth
- Molecular evidence for evolutionary relationships examples
- Carbon 14 dating 1
- DNA spells evolution
- Variation in a species
- Reproductive isolation
- Evidence for evolution
- Surviving an extinction level event
- Cellular evidence of common ancestry
- A brief history of mass extinctions
- Evidence of evolution
- Common ancestry and continuing evolution
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Molecular evidence for evolutionary relationships examples
Two example items (from NY Regents exams) using molecular evidence to think about how closely related different species are.
Want to join the conversation?
- Shouldn't the last one be B A C since A and C are more similar than B and C?(6 votes)
- I don't really think that matters. I guess the only factor determines how close they are genetically in this diagram is the closeness of their common link as compared with other species.(4 votes)
- is it possible for an organism, say a plant, to be genetically similar or another plant, and less genetically similar to another plant, but have the genetically unsimilar plant to actually be more closely related on an evolutionary time scale?(3 votes)
- I guess that's theoretically possible because the genes of an organism aren't JUST affected by their ancestors but also by the environment in which they live in. So, possibly species which are closer to other species on the evolutionary time scale may be genetically similar to another species though they might not share a nearer common ancestor mainly because they have evolved to live in a different habitat.(4 votes)
- Can some one please summarize the whole thing?(3 votes)
- Is Gel Electrophoresis done using chromatography?(2 votes)
- No. Gel Electrophoresis is its own form of a biotechnological process in which DNA is cut up using restriction enzymes and then run in a positively charged agar to separate the pieces and create "bands" of DNA.(3 votes)
Video transcript
- [Instructor] 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 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
'cause it is itself. And then this is the gel
electrophoresis banding pattern. So what we wanna 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 it, 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 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, and 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, and we could say, and least
different amino acid sequences, and tests positive for 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 ask 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 two, observe behavioral and physical characteristics
of all the finches and group them by similarities. C, obtain molecular evidence
from all three species and identify similarities. Four, 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 similar that DNA probably is. And so they're 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 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 may be one of the
physical characteristics that they're looking at, but we know for sure that they're 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 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 recent common ancestor than 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 here has 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 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.