<< Chapter < Page Chapter >> Page >

Building phylogenetic trees

How do scientists construct phylogenetic trees? After the homologous and analogous traits are sorted, scientists often organize the homologous traits using a system called cladistics    . This system sorts organisms into clades: groups of organisms that descended from a single ancestor. For example, in [link] , all of the organisms in the orange region evolved from a single ancestor that had amniotic eggs. Consequently, all of these organisms also have amniotic eggs and make a single clade, also called a monophyletic group    . Clades must include all of the descendants from a branch point.

Art connection

The illustration shows the V-shaped Vertebrata clade, which includes lancelets, lampreys, fish, lizards, rabbits, and humans. Lancelets are at the left tip of the V, and humans are at the right tip. Four more lines are drawn parallel to the lancelet line; each of these lines starts further up the right arm of the V than the next. At the end of each line, from left to right, are lampreys, fish, lizards, and rabbits. Lizards, rabbits, and humans are in the clade Amniota, which form a small V nested in the upper right-hand corner of the V-shaped Vertebrata clade.
Lizards, rabbits, and humans all descend from a common ancestor that had an amniotic egg. Thus, lizards, rabbits, and humans all belong to the clade Amniota. Vertebrata is a larger clade that also includes fish and lamprey.

Which animals in this figure belong to a clade that includes animals with hair? Which evolved first, hair or the amniotic egg?

Clades can vary in size depending on which branch point is being referenced. The important factor is that all of the organisms in the clade or monophyletic group stem from a single point on the tree. This can be remembered because monophyletic breaks down into “mono,” meaning one, and “phyletic,” meaning evolutionary relationship. [link] shows various examples of clades. Notice how each clade comes from a single point, whereas the non-clade groups show branches that do not share a single point.

Art connection

Illustrations show a phylogenetic tree that includes eukaryotic species. A central line represents the trunk of the tree. From this trunk, various groups branch. In order from the bottom, these are diplomonads, microsporidia, trichomonads, flagellates, entamoebae, slime molds, and ciliates. At the top of the tree, animals, fungi and plants all branch from the same point and are shaded to show that they belong in the same clade. Flagellates are on a branch by themselves, and they also form their own clade and are shaded to show this. In another image, Flagellates and ciliates are shaded to show that they branch from different points on the tree and are not considered clades. Likewise, a grouping of animals and plants but not fungi would not be considered a clade cannot exclude a branch originating at the same point as the others.
All the organisms within a clade stem from a single point on the tree. A clade may contain multiple groups, as in the case of animals, fungi and plants, or a single group, as in the case of flagellates. Groups that diverge at a different branch point, or that do not include all groups in a single branch point, are not considered clades.

What is the largest clade in this diagram?

Shared characteristics

Organisms evolve from common ancestors and then diversify. Scientists use the phrase “descent with modification” because even though related organisms have many of the same characteristics and genetic codes, changes occur. This pattern repeats over and over as one goes through the phylogenetic tree of life:

  1. A change in the genetic makeup of an organism leads to a new trait which becomes prevalent in the group.
  2. Many organisms descend from this point and have this trait.
  3. New variations continue to arise: some are adaptive and persist, leading to new traits.
  4. With new traits, a new branch point is determined (go back to step 1 and repeat).

If a characteristic is found in the ancestor of a group, it is considered a shared ancestral character    because all of the organisms in the taxon or clade have that trait. The vertebrate in [link] is a shared ancestral character. Now consider the amniotic egg characteristic in the same figure. Only some of the organisms in [link] have this trait, and to those that do, it is called a shared derived character    because this trait derived at some point but does not include all of the ancestors in the tree.

Questions & Answers

what is biochemistry
Is talking about the little study out of chemistry
Is talking about the little study out of chemistry
How many cells does a human being have?
Awamalego Reply
How many cells does human being have?
How many cells does human being have?
countless cells
what is the function of a skeleton
Julien Reply
it supports and gives the appearance of the body.
mandle experiment point
Sarpz Reply
what is the mean of biology
In a lay man definition biology talks about life as a whole
the study of living organisms
the study of the structure, function, and origin of living organisms
biology has many branches. Botany (the study of plants) , evolution,. Ecology (how animals interact amongst each other. the study the habitat of an animal and try to determine as well as find strategies to prevent a species from going extinct.
is simply the study of life
what is a specicide
Twinkl Reply
why are mosquitoes primary and secondary consumers
what are the structures found in all viruses
how does vaccinating a woman prevent her baby from getting the illness?
how does selective breeding increase crop size
wat is an animal cell
Monicah Reply
what is deer
Khansawu Reply
breathing in reptiles
sam Reply
which molecules binds to the active site of an enzyme
Ghulam Reply
please remind me
please I do not no
please remind me
please I do not no
please remind me
what is nutrients
Patrick Reply
nutrients is substance which body use in terms of need
can I join?
substance that provides nourishment essential for the maintenance of life and for growth.
right same answer as you Umar
please remind me
Any material that provide essential components for cell metabolisms is nutrient
what are the types of skeleton
Tanyi Reply
endo skeleton and exo skeleton
or types of skeletons There is exo skeleton found in class insecta Exo skeleton found in phylum chordata and lastly hydrostatic skeleton found mainly in earth worms
and hydrostatic skeleton
endo, exo and hydrostatic skeleton
what is life?
Jerson Reply
life is when any living thing breath or respirate.
I want to join
me too
me two
me too
me too
I here
Does anybody knows another biology app that brings good understand
give an example of a phylum where all members have open circulatory
Omoro Reply
phylum Anthropoda
how do u change the unit of temperature from degree celsius to degree Fahrenheit
what are beneficial effects in industrial
Nnamani Reply
create employment
provide food
dirty the environment
pollution and lack of knowledge about how to manage waste
what is gametophyte
Ibrahim Reply

Get the best Biology course in your pocket!

Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?