How To Make A Cladogram
Cladogram: A cladogram is a diagram used to represent a hypothetical relationship between groups of animals, called a phylogeny. A cladogram is used by a scientist studying phylogenetic systematics to visualize the groups of organisms being compared, how they are related, and their most common ancestors. A cladogram can be simple, comparing only two or three groups of organisms, or it can be enormously complex and contain all the known forms of life.
Cladogram design is universal, although simple. A cladogram consists of the organisms being studied, lines, and nodes where those lines cross. The lines represent evolutionary time, or a series of organisms that lead to the population it connects to. Nodes represent common ancestors between species. At some point in the past a population of common ancestor organisms was divided, giving rise to the different organisms being studied. Some cladograms show evolutionary time through the scale of the lines, longer lines meaning more time. Some cladograms chose to show extinct species, while others omit them. Any particular cladogram is formulated specifically for the use it is needed.
A cladogram gets its name from the clades, or groups of organisms that are displayed. A clade is a group of living organisms and the common ancestor they are derived from. Scientist use synapomophies, or shared derived characters, to define these groups. For instance, mammary glands are a shared characteristic of mammals. All mammals and their oldest common ancestor, had or have mammary glands. Thus, if we are looking at an unidentified animal and trying to place it in a cladogram, if it has mammary glands we know it belongs in that branch. Symplesiomorphies, by contrast, are characters that all organisms in the cladogram have. If the cladogram including the mammals was of all vertebrates, then the presence of vertebrae in our unknown animal would be a symplesiomorphy. Symplesiomorphies do not tell us anything about the relatedness of different groups in a cladogram, because all the organisms have (or had), that characteristic. A very simple cladogram of the vertebrates can be seen below.
A cladogram is a chart that is composed of many different clades or branches. Don’t worry – we’ll explain that sentence in more detail in a minute. A cladogram might remind you of a family tree since it too has many different branches, but it’s set up in a slightly different format than a typical tree. It functions similarly to a family tree since the organisms listed are all related, but it is much more than just that.
Cladistics is a branch of scientific classification that deals with the organization of related organisms based on their last common ancestors. Scientists look at an organism’s features and see how closely they are related to other organisms based on features found in recent ancestors (rather than ancient ones). When cladistics first came about, researchers would look at the morphological (physical features) data of organisms. As science has progressed, we now look at the DNA sequencing data as this can tell a story not seen be physical features.
When we look at cladistics, we find that the closer the ancestor is to a group, the more closely they are related. When we begin to chart these closely-related organisms, we start to form clades. A clade is a small branch or section in cladistics used to chart connections between organisms. It does so by connecting an organism to its particular ancestors or descendants.
What does a Cladogram show?
What is Phylogram and Cladogram?
How do you make a Cladogram?
- Step 1: Pick Organisms for Your Cladogram. …
- Step 2: Pick One Ancestral and One Derived Characteristic to Designate the Outgroup. …
- Step 3: Pick Derived Characteristics for the Ingroup (Part 1) …
- Step 4: Pick Derived Characteristics for the Ingroup (Part 2) …
- Step 5: Pick Derived Characteristics for the Ingroup (Summary)
How To Read A Cladogram
We sometimes use family trees to show relationships between individuals. Those who are closely related are located closer together than those who are only distantly related.
Both cladograms and phylogenetic trees show relationships among organisms, how alike, or similar, they might be. We can see a typical cladogram and phylogenetic tree here.This same idea of relationships can be used in science. Biologists use cladograms and phylogenetic trees to illustrate relationships among organisms and evolutionary relationships for organisms with a shared common ancestor.
On the other hand, the branches on a phylogenetic tree can be proportional to the amount of change or evolutionary time. So, you can also track how species have changed over time. Species are still grouped according to similarities and physical or genetic characteristics – for example, the presence or absence of gills. But, a phylogenetic tree describes an evolutionary history by showing how ancestors are related to their descendants and how much those descendants have changed over time.First, a cladogram can look at trees that may have been derived from a common ancestor to arrange organisms on different branches. But those branches used aren’t representative of the relative amount of change or evolutionary time that has occurred between organisms. Plus, a cladogram doesn’t necessarily show exact relationships between ancestors and descendants.
There are further distinctions, and to further complicate matters, different analyses and new information can yield different possible evolutionary relationships. Luckily, for the scope of this lesson, you can think of a phylogenetic tree as a cladogram with a few added bells and whistles.
How To Make A Cladogram
A clade is a group of species used in cladograms (and phylogenetic trees), which consists of one ancestor and all its descendants. The term clade comes from the Greek word klados, which means branch. Relating this back to our family tree – one clade would consist of the great-great grandparents, all the way down to the siblings.
Just like there are different types of families, there are different types of clades. The three major types are: monophyletic, paraphyletic and polyphyletic.
Monophyletic refers to just one clade; meaning these terms are interchangeable. ‘Mono-‘ means ‘one,’ making this easy to remember. As stated before, a monophyletic clade includes one ancestor and all of its descendants. An example of this would be the genus Homo. This genus includes all the species from ancestral humans up to modern-day humans, or Homo sapiens. We can see an example of a monophyletic clade here.
Cladogram MakerPolyphyletic groups are characterized by the presence of homoplasies, or characteristics which appear similar, giving the impression they were inherited from a common ancestor, but in actuality, they weren’t. This means that instead of sharing one common ancestor, these groups have multiple origins. Polyphyletic groups can be confusing, and phylogenists and cladists rarely use them. The best examples of a polyphyletic group are the pachyderms, or elephants, rhinos and hippopotamuses. These animals each have their own common ancestor, but are grouped together as a polyphyletic group because they all share a similar thick, wrinkled skin and hooves. (‘Pachy’ means ‘thick,’ and ‘derm’ refers to the skin.) We can see a polyphyletic clade here.A group is said to be paraphyletic if it consists of all the descendants of an ancestor minus one or two small groups. The prefix ‘Para-‘ means ‘around’ or ‘surrounding.’ A good example of a paraphyletic clade is the reptiles. Reptiles, mammals and birds all share a common ancestor. However, the reptiles form a paraphyletic clade to the other two groups. We can see an example of a paraphyletic clade here.