D.5b: Phylogeny & systematics

30/09/2013 § Leave a comment

What’s kicking, HL bio suckers? How were your weekends? Oh, no, wait – actually, I really don’t care. Because I have to work. I’ll “care” after May of 2014 when the exams are over. For now, let’s talk Cladistics because clearly I have nothing better to do.

You want definitions, yeah, okay, I’ll give you definitions. Cladograms are tree diagrams that visually represent clades, which are groups of organisms that evolved from a common ancestor. On a cladogram, there are branching points (because it’s a tree diagram, get it?) that indicate which groups of organisms are related. This method of taxonomy/classification is special and new from what old, old, old men use, so it has a new name: cladistics, which can be defined as a method of classification of living organisms based on the construction and analysis of cladograms.

But okay, on the topic of cladistics and cladograms. Because cladograms integrate nodes into their structure, branching out can happen at any time, which sort of contradicts traditional classification. Some cladistics suggest completely different phylogenies from traditional classifications. The positive sides of cladistics are objective and not based on only morphologies but on molecular differences in species. On the other hand, molecular differences between species are based mostly on probability. Generally, cladistics can still make errors in its predictions and classifications.

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D.5a: Phylogeny & systematics

26/09/2013 § Leave a comment

Ah, finally, a proper blog post. This one’s about classification and phylogeny (ooh, bad flashback to lab #1). Why do scientists classify living organisms? Why else! The three primary reasons for classifying organism is

  1. species identification: in order to know which species belong together
  2. predictive value: many members in a group will have similar characteristics
  3. evolutionary links: if the members in a group have similar characteristics, then they probably evolved from a common ancestor

Classification is important because some species share traits with other species that be analogous or homologous structures. An analogous structures have a common function but a different evolutionary origin, while homologous structures have a common evolutionary origin but have different functions (so they’re flip-flopped). Analogous structures are the human and octopus eye, and wings. Homologous structures include the chicken wing and human arm, as well as the oh-so-famous pentadactyl limb in mammals.

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D.3c: Human Evolution

24/09/2013 § 1 Comment

Hahahahaha, there is no reading involved in this particular blog because we read it for the last one??? What is going on with my life?

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D.3b: Hominid Evolution

23/09/2013 § Leave a comment

This is the strangest blog I’ve ever written for this class.

There are two types of evolution. Jon talked about it last Thursday and I didn’t believe him but he was telling the truth. There is cultural evolution which are new methods, inventions or customs that can be passed on easily. Then there is genetic evolution, which involves natal selection between inherited differences.

/looks at DBQ – You’ve got to be kidding me.

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D.3a: Primate Evolution

23/09/2013 § Leave a comment

I’m so sorry, I’m so so so sorry, I know this is late (shh) but let’s talk about hominids and primates and skulls. Primates belong to the order of mammals and include apes, monkeys, tarsiers (which can be found in Bohol, Philippines, and they are warm and harmless and utterly adorable) and lemurs. Humans are also classified as primates because we share the characteristics of the other members in the order. These include:

  1. grasping limbs (four fingers and an opposable thumb, thank you Ross Geller)
  2. mobile arms (that can move in three planes)
  3. forward facing (or stereoscopic) vision
  4. skulls made for remaining upright

Some important observed evolutionary trends to note because I’m trying to make the writing part of this blog faster than usual:

  • species in the family Hominidae show increasing adaptation of bipedalism
  • ^ the above also show an increasing brain size relative to body size (their heads got bigger)

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D.2d: Species and Speciation: Macroevolution

05/09/2013 § Leave a comment

It’s 4 in the morning and I’m doing bio homework, what’s new? (It’s okay, dudes, I slept for like six hours before this.) LET ME TELL YOU WHAT’S NEW. Divergent evolution and adaptive radiation, that’s what’s new! I think Mr. Ferguson would call all this macroevolution (hence the title of the blog) because the little speciations and evolutionary achievements work together to make big evolutionary changes.

Divergent evolution is when species evolve in different ways, normally by adapting to different ecological conditions so that they avoid competition with each other. When species diversify this way, it is called adaptive radiation (which is kind of vague to me because that’s, like, two words to fit into one definition?). An example of adaptive radiation, you ask? NO PROBLEM, MAN. You know marsupials? Yeah, well, the ancestral marsupials are responsible for the speciation of today’s koalas, wombats, and kangaroos. COOL? Yes, cool.

When natural selection acts the same way in different parts of the world (presumably because of similar environmental conditions), species can become very similar even if they are not related to each other – this is called convergent evolution (kind of like the opposite to adaptive radiation). Basically, unrelated species showing striking similarities = convergent evolution; related species showing striking differences = divergent evolution. GOT IT???

Finally, there is one idea on the rate of evolution called gradualism where evolution moves slowly but the little changes make large changes over time. Sound familiar? Yeah, sounds pretty friggin’ familiar to me, and it’s called macroevolution, you dingbats. However, there’s another idea called punctuated equilibrium which goes: periods of stability followed by short periods of rapid change, which suggest that a species is well-adapted during the periods of stability and natural selection chooses for them to maintain their characteristics, and in the periods of rapid change, drastic environmental changes (e.g. volcanic eruptions) are what cause natural selection to choose new characteristics.

…and that’s all for now, folks. Ohmygod there’s a test soon, ohmygod ohmogdyigdo ogdhkmdf.

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D.2c: Species and Speciation: Sympatric Speciation

03/09/2013 § 1 Comment

It is with deep and utter sadness that I report to this blog that some animals and plants are unable to reproduce. What a sad, sad day it is.

Okay, in all seriousness, there is a reason why most plants and some less complex animals can’t make babies (therefore they are sterile or infertile). This occurs with polyploid organisms, which means that they have more than two sets of homologous chromosomes as a result of hybridisation between two different species. This is all centred on the number of homologous chromosomes an organism has and whether or not it’s viable for meiosis during reproduction. A tetraploid, for example, has an even number of homologous chromosomes and the gametes would then be diploid. If tetraploids mate with tetraploids, then the number of sets for the kid would still be okay. If a tetraploid (gametes are diploid) mates with a diploid (gametes are haploid), then the offspring would be at a disadvantage because it would be triploid. It wouldn’t be successful in meiosis therefore wouldn’t be able to reproduce any of its own offspring essentially rendering it reproductively isolated from the rest of the original population. Too bad, son.

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