Friday, April 9, 2010

Morphological v. Molecular

This year we learned about two kinds of phylogenetic trees. Originally scientists based the organization of this tree on morphological and developmental data. However, new molecular data such as DNA sequences have provided another source of information in order to determine common ancestry. What similarities or agreements exist between morphological and molecular trees? How are they different?

Coyne brings up the point that certain groups of organisms are considered to be separate species even though they look exactly alike. For example, the group of fruit flies, Drosophila, is recognized as nine separate species due to differences in where they live and who they bite. Conversely, there are groups like humans that look very different, yet still have the ability to successfully mate together and are considered the same species. This brings up the question on whether or not "designation of species is an arbitrary exercise" or not (171). Therefore, what advantages are there to organizing the species into phylogenetic trees even through there are obvious inconsistencies and debates within the system?


  1. There are two types of ancestrial trees. One is the morphological ancestrial tree and the other is the molecular ancestrial tree. The main focus of the morphological tree is that the morphological tree focuses on the similarity of the anatomical features. This means that species that displays similar anatomical features are more closely related, meaning have branched off most recently. Molecular tree focuses on the similarity of the DNA sequences and the presentation of the molecular features such as similar proteins. The similarity is that usually the gene expression and the presence of certain proteins are parrellel to the presence of the anatomical feature of the organism. This shows the similarity of the two trees as majority of the classification is similar. The specificity of the agreement of the morphorlogical and molecular phylogenic tree is that one, all animals share a common ancester; two, sponges are basal animals; three, eumetazoa is a clade of animals with true tissues; four, most animal phyla belong to the clade bilateria; and lastly, chordates and some other phyla belong to the clade deuterostomia. The differences arise from detailed tree, such as the place of Acoela and other classes of the tree.
    The advantages to organizing the species ieven though there are obvious inconsistencies and debates is that by creating a phylogenetic tree and bringing up evidences to prove them true, biologists can catagorize millions of species on Earth. A lot of species "look either exactly alike or nearly alike." (Coyne 171). One of the advantages of this, given in the book, is that a specie Anopheles gambiae is one of the species that has 6 other specie that looks similar to. In order to fight the diease, malaria, that is carried within this specie, it is advantageous for a doctor to know where the disease occured because Anopheles gambiae lives in a different niche than other species. This allows a improved treatment in the medical world. Another reason is because when humans compare two different species, people often makes generalizations about where the species ancestrate from. By creating a phylogenetic tree, this generalizations can be solved, although not completely solved since there are much debates on the completio of the phylogenetic trees.


    Why Evolution is True by Jerry Coyne

    Campbell Biology Eighth Edition Campbell-Reece

  2. The classification of species has been a long-time debate. When Coyne question, “At what point are differences between populations large enough to make us call them different species?” (171) is the question taxonomists have debated. While understanding that two species are named different when they cannot mate with each other, there are other characteristics involved.
    Because of the recent molecular data such as DNA has provided an additional source for defining clades, the debate between using the traditional morphological characters or the new molecular sequences has been an ongoing debate. Like liondrummer mentions, so far, there are five points of agreement between the morphological and the molecular trees; but the differences, more specifically differ on where the trees branch and into which classifications. The morphology-based tree divides the bilaterians into two clades: deuterostomes and protostomes (these two modes of development reflect a phylogenetic pattern) while within the protostomes, arthropods are grouped with annelids because both groups have segmented bodies. But when analyzing molecular data, Hox genes provide a different explanation. Based on Hox genes, ribosomal genes, etc, studies indicate that there are three major clades of bilaterally symmetrical animals: Deuterostomia, Lophotrochozoa, and Ecdysozoa. Also, this holds that arthropods and annelids are not closely related. Therefore, it can be seen that animal systematics is still at work (Campbell 662-664).
    Even thought there are conflicts, and not one way of classification is the most correct, creating molecular and morphology-based trees shows that we are one step closer to classifying the millions of species. Besides medical use, as liondrummer mentions, an important reason for classification is to trace the lineage of certain species and to corroborate evidence that evolution does exist. For example, take lizards and snakes: the Australian legless lizard known as the common scaly-foot is many times mistaken to be a snake. But by examining that it also does not have a fused eyelid, a highly mobile jaw, or a short tail posterior to the anus (characteristics of snakes), it is inferred the animal is indeed a lizard. By tracing the phylogeny, this shows that both the scaly-food and snakes evolved from lizards with legs, but different lineages. Another example deals with the global health issue: by tracing the DNA phylogeny of maize, the second most important food source behind wheat, wild grasses that may carry beneficial genes may be used to cultivate maize by genetic engineering. Other uses include tracing the illegal selling of certain “whale meat” or tracing the harmful train of bacteria used in the bioterrorism anthrax bacteria case in 2001. (Campbell Ch 26)

    Sources: Coyne / Campbell

  3. I dabbed on over 9000 of these memes and am still not certain about which joint to blaze....
    But then again, as one of the great minds of this age said "Rawr XD." I guess this reveals something inside of us. Something dark that we hold burning next to our heart. "Rawr XD" we hear. ":3 nuzzles" we say. Is this the real life? Is this just fantasy? Although I belive that maximum parsimony is easier to reach (in terms of conflict, especially in the case of an unresolved branch) with a genetic tree, any discussion of this sort begs the question of why we catagorize. I have an increddibly interesting theory on this, although I'll give you guys an abridged version:
    1: XD has 2 letters
    2: every XD goes with a dab
    3: dab is 1 word
    4: 2+1 is 3
    5: A triangle has 3 points
    6: The Illuminati is symbolically linked to triangles
    7: The Illuminati and XD are the same
    8: simmilarity
    9: identical twins are simmilar
    10: Frank Craighead and John Craighead are twins
    11: Frank Craighead and John Craighead are scientists
    12: phylogenies are scientific
    13: Phylogenies are illuminati conf1rmed

    Open your third eye. Remember, remember

    -London Prevails

    -The anarchist, the Painter of Signs, the BOFH

    Rawr XD