Tuesday, March 31, 2009
Genealogical Trees?
Why is it so important from a scientific standpoint to have genealogical trees? Scientists have spent hundreds of years slaving over newer and better methods to categorize all organisms into groups. Why is it so important? Examine the different attempts over the years to create trees. How are they different and similar? How are the organisms categorized in each tree, and why is it significant? Discuss terms like kingdom, domain, etc and discuss what they mean.
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Creating trees to properly classify organisms is very important because it allows scientists to do exactly what Carroll is doing in his book and look for relationships between species and predict the reasons behind different relationships. If scientists have the relationships wrong, then the inferences made about species will most likely be wrong as well. This is why, according to Carroll, DNA is the only reliable method in creating these trees.
ReplyDeleteA supporter of using DNA has a lot of evidence to use against other methods such as nutrition type and physiological traits. For example, the highest division of organisms was a five-kingdom system made up of Monera, Protista, Plantae, Fungi, and Animalia. This system was developed based on nutrition types of the different organisms. We now know due to DNA sequencing that four of those divisions, Plantae, Fungi, Protista, and Animalia, are much more related than with Monera, so certain changes were made in which we now have a three-domain system of Bacteria, Archaea, and Eukarya. Within Eukarya there are the kingdoms Protista, Animalia, Fungi, and Plantae. Kingdom Monera of the old system was divided into Domain Bacteria and Archaea. If scientists had been mistaken for so many years on the true relationships between different species, it was impossible for them to draw accurate conclusions as to which species were related, how close they were related, how far back in the history of life did the common ancestor split into those two species, and more. A common use for these genealogical trees that Carroll discusses in the book is to determine whether a trait evolved independently in two different species or whether they both inherited it from a common ancestor. For example, let’s say we want to see if colored vision in two species has independently evolved or was inherited. Let’s call those species A and D. In our relationship tree it states that the common ancestor splits off many times resulting in species A, B, C, and D, all descendents of the common ancestor. We know that A and D have colored vision, but B and C do not, so we conclude that since a trait inherited by the ancestor would be found in B and C as well, colored vision must have evolved independently in A and D. Well, what if our tree was wrong? What if B and C were actually NOT descendents of the common ancestor? All our conclusions have been shot, and this makes it clear why having an accurate genealogical tree is so important. The only way to be sure now of an organism’s history is through its DNA. DNA sequencing to examine fossilized genes and current genes and percent similarities of DNA sequences among different species is an accurate method of measuring the relatedness of species.
Genealogical trees are important in order to classify organisms into categories. This helps us understand their ancestors and physical and chemical components that may connect them with other organisms. Carroll states that DNA should be the only characteristic that classifys the organisms into each category.
ReplyDeleteAn early genealogical tree was composed of five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia. The characteristics that classified organisms in each class were the organism’s nutrition. For each kingdom the organisms are classified into further specific groups involving their phylum, class, order, family, genus, and species. Scientist conducted much research and this basic genealogical tree changed often. Bacteria, Archaea, and Eukarya were the domains in which organisms were classified.
Using these trees a scientist can research and understand different origins that an organism has evolved from. Relationships with other species and organisms can also provide information that may be missed without the organization of a genealogical tree. Carroll states that a scientist may be researching a specific gene, and in order to understand where the gene evolved from he/she can use a genealogical tree of the organisms which have this gene. By using the genealogical tree, he/she may see the organism evolve from a common ancestor or individually.
Making sure that our genealogical trees are accurate is very important; scientists rely greatly on these trees to receive information about evolution through different species. DNA will ensure that the tree is accurate and scientist should rely on DNA to form the genealogical trees (just like Carroll suggests).
http://biology.suite101.com/article.cfm/five_kingdoms_of_life
^ ** explains each kingdom in greater depth**
Genealogical trees, or phylogenetic trees, allows scientists to map out speciation due to selective or random splitting in organism lineages. The two types of trees, rooted and unrooted, allow insight into the common ancestor of the organisms mapped, rooted trees being sure of a common ancester and unrooted trees not making assumptions about such facts.
ReplyDeleteThe first trees of life, formulated by Greeks Aristotle and Linneus, classified animals and plant based of methods of reproduction. Their other criteria for classification were very phylosophical, getting more general as they progressed into larger taxonomical labels.
Swiss professor Conrad Gesner began to classify animals into smaller groups to allow for easier classification but in an either/or method of classification. This begun to be disputed into the 17th and 18th centuries, when scientists began to propose multiple sub categorizations. Up until Linnean 5 category taxonomy, the biological classification methods changed much and often.
http://en.wikipedia.org/wiki/Biological_classification
http://en.wikipedia.org/wiki/Phylogenetic_tree
Biologists have various methods of creating such trees through classification and division; there are four concepts through which biologists analyze species: the ecological species concept, the pluralistic concept, the morphological concept, and the genealogical species concept.
ReplyDeleteEcological Species Concept - "defines a species in terms of its ecological niche, the set of environmental resources a species uses," (Campbell 468).
Pluralistic Species Concept - "the factors that are most important for the cohesion of individuals species vary. In some cases, reproductive isolation may be a key unifying factor for a species. In other cases, adaptation to a specific ecological niche may be the main factor in species cohesion. In still other cases, the integrity of the species may depend on some combination of reproductive isolation and a unique niche," (Campbell 468).
Morphological Species Concept - "characterizes each species in terms of a unique set of structural features, remains the way we distinguish most species," (Campbell 468).
Genealogical Species Concept - "defines a species as a set of organisms with a unique genetic history - that is, as one tip on the branching tree of life. The sequencing of nucleic acids and proteins provides data that researchers are now using to define each species in terms of unique genetic markers," (Campbell 468).
With each of these concepts now established, let's turn to the main task at hand. Genealogical trees are made using the concepts as above. According to Sean Carroll, however, a better way to decipher a specie's relationship with another specie is through the genealogical species concept. "It also relies on DNA, but rather than being based on the degree of sequence similarity, it looks for the presence and absence of certain landmarks in specific places in species DNA. These landmarks are produced by accidental insertions of junk DNA sequences near genes. Particular chunks of junk DNA, called long interspersed elements (LINES) and short interspersed elements (SINES)," (Carroll 99). Using physical genetic markers established during mapping, as on Campbell page 389, biologists can compare LINES and SINES to that of other organisms. The steps for making a tree are outlined (and condensed here for the purpose of informing) on page 99 in Making of the Fittest.
To Make A Genealogical Tree:
1. Identify a set of SINES to be surveyed in one species.
2. Specific regions of another species are examined.
3. Analysis confers: if another species' DNA contains the same SINE as that in one species or close to the number of base pairs extension by that of a SINE, there is a kinship/relationship.
Most of the recent genealogical trees today are in forming the invertebrate/vertebrate trees. Take a look at the trees on page 636, 640, and 694 in Campbell. The traditional trees are based upon body-plan grades for page 636, but the next tree is based upon sequencing of small subunit ribosomal RNA (SSU-rRNA) - page 640. On the 636 tree, there are dotted lines to show the incongruities between the placement of phyla; however, with the newer version of the tree, there are no incongruities based on the SSU-rRNA. Similarly the 694 tree is shaped with such markers. The trees that are considered more accurate are those that are much more inclusive and rely upon the genetic markers since they carry the scars of evolution. The only way such trees can be made obsolete is to spend time creating genealogical trees. Without such time being spent, there would be no relationships and the biologists would have to sit around for their beards to grow. All in all, the majority of this discussion relates to the biological theme of evolution: using different means to come to a conclusion upon the relative kinship between species.