A cladogram is a diagram that shows the relationships among different groups of organisms based on their shared characteristics. It can help us understand how organisms evolved from a common ancestor and which ones are more closely related to each other. In this article, we will use a cladogram to answer the question: which organism is most closely related to Arabidopsis?
Contents
What is Arabidopsis?
Arabidopsis is a genus of flowering plants that belongs to the mustard family (Brassicaceae). It contains about 10 species, but the most widely studied one is Arabidopsis thaliana, also known as thale cress or mouse-ear cress. Arabidopsis thaliana is a small, annual plant that grows in temperate regions of the world. It has a simple genome, a short life cycle, and a small size, making it an ideal model organism for plant biology research. Arabidopsis thaliana was the first plant to have its entire genome sequenced in 2000.
How to Construct a Cladogram?
To construct a cladogram, we need to identify the characters or traits that distinguish different groups of organisms. These characters can be morphological (based on physical features), molecular (based on DNA or protein sequences), or behavioral (based on habits or behaviors). We also need to determine which characters are ancestral (shared by all members of a group) and which are derived (unique to some members of a group). Ancestral characters are called plesiomorphies, while derived characters are called synapomorphies.
We can use a table to organize the characters and the groups of organisms. For example, let’s say we want to compare Arabidopsis with three other plants: soybean, papaya, and grape. We can choose four characters that are relevant for these plants: seed type, flower type, fruit type, and genome size. We can assign each character a value of 0 or 1 depending on whether it is present or absent in each plant. For example, if a plant has dicot seeds (seeds with two cotyledons or seed leaves), we assign it a value of 1 for seed type; if it has monocot seeds (seeds with one cotyledon), we assign it a value of 0. We can do the same for the other characters.
| Plant | Seed type | Flower type | Fruit type | Genome size |
| Arabidopsis | 1 | 1 | 0 | 0 |
| Soybean | 1 | 1 | 1 | 1 |
| Papaya | 1 | 0 | 1 | 0 |
| Grape | 0 | 0 | 1 | 0 |
Next, we need to find the most parsimonious cladogram, which is the one that requires the fewest changes in character states to explain the observed data. We can use various methods to do this, such as maximum parsimony, maximum likelihood, or Bayesian inference. For simplicity, we will use maximum parsimony here.
We start by choosing one plant as the outgroup, which is the one that is most distantly related to the others. In this case, we can choose grape as the outgroup because it has monocot seeds, which is an ancestral character for all flowering plants. Then we draw a line from grape to a branching point, where we split the remaining plants into two groups based on their shared derived characters (synapomorphies). For example, we can split soybean and Arabidopsis from papaya based on their flower type: soybean and Arabidopsis have actinomorphic flowers (flowers with radial symmetry), while papaya has zygomorphic flowers (flowers with bilateral symmetry). This branching point represents a hypothetical common ancestor that had actinomorphic flowers.
We repeat this process until we reach the tips of the cladogram, where we place the names of the plants. We also label each branching point with the synapomorphy that defines it. The result is a cladogram like this:
Which Organism is Most Closely Related to Arabidopsis?
According to the cladogram above, we can see that soybean is the organism that is most closely related to Arabidopsis among the three plants we compared. They share two synapomorphies: dicot seeds and actinomorphic flowers. They also differ in two characters: fruit type and genome size. Soybean has legume fruits (pods) and a larger genome than Arabidopsis, which has silique fruits (dry capsules) and a smaller genome.
We can also see that papaya is more closely related to Arabidopsis than grape, because they share one synapomorphy: dicot seeds. They differ in three characters: flower type, fruit type, and genome size. Papaya has zygomorphic flowers, berry fruits, and a medium-sized genome, while grape has actinomorphic flowers, berry fruits, and a small genome.
Conclusion
In this article, we used a cladogram to answer the question: which organism is most closely related to Arabidopsis? We found that soybean is the closest relative of Arabidopsis among the three plants we compared, followed by papaya and grape. We also explained how to construct a cladogram using characters and parsimony. We hope this article was helpful and informative for you.
According to Wikipedia, a cladogram is a diagram used in cladistics to show relations among organisms. According to uky.edu, a cladogram of Arabidopsis and soybean late embryogenesis abundant proteins shows their similarities and differences. According to plos.figshare.com, a cladogram of the key species used in this study shows the divergence times of Arabidopsis, papaya, and grape.
