(TX) Modern Classification: Phylogeny and Cladograms Lesson

Biology_LessonTopBanner.png

Modern Classification: Phylogeny and Cladograms

Today, scientists do look at organisms' physical features, but mostly they group organisms based on evolutionary classification or phylogeny. Phylogeny is the study of evolutionary relationships among organisms. Scientists construct diagrams called cladograms (a tree-like diagram) that shows evolutionary relationships among organisms.

BIO19_family-genealogy-tree-diagram-chart_3446-331.jpg

Modern Classification

Watch the presentation below to learn more about classification. 

What is a Molecular Clock?

No, it is not a new alarm app for your phone. A molecular clock allows scientists to estimate the amount of time that two species diverged from each other. How do they do this? Scientists compare the number of mutations among their sequences. Mutations can serve as molecular clocks because they accumulate at a fairly predictable, steady rate. The mutations we are talking about are neutral mutations (mutations that have neither a positive or negative effect).

 BIO19_MolecularClock.png

Mutations

Examine the picture below that shows the DNA sequences of three related organisms, one of which is an ancestor (perhaps preserved DNA from a now-extinct species). You can see that the number of mutations in these related species shows which are the oldest and those that evolved more recently. 

BIO19_Mutations.png

In this case, Organism 2 is the more recently evolved species.

Molecular clocks can be used with nuclear DNA or mitochondrial DNA (remember that mitochondria have their own DNA). Looking at mitochondrial DNA is interesting because mitochondria DNA is only inherited from your mother (you get your mitochondrial from mom's egg).

BIO19_DNACHART.png

Watch the video below from DNAinteractive that explains how we can construct a maternal ancestry by using mitochondrial DNA as a molecular clock.

Similarities in DNA can help determine appropriate classification and are evidence of common ancestry. All organisms use DNA and RNA to pass on information, therefore, DNA evidence can help show how species have changed over time.

Modern Classification Challenge and Before You Go

Practice Time! Use the knowledge you learned from the lesson to complete the practice activities below.

Before You Go - You Need To Know

shutterstock_1109171282.png

The following key points are from the explore section of the lesson. You must know the following information before moving to the next lesson. This is just a summary of the key points.
  • What is phylogeny?
    • The study of evolutionary relationships among organisms.
  • What is a cladogram?
    • A tree-like diagram that shows evolutionary relationships about organisms.
  • What are the derived characteristics?
    • Evolutionary innovations or adaptations (feathers, limbs, eggs, etc.) in organisms that were not present in their ancestors.

BottomBanner_Bioloby.png

IMAGES CREATED BY GAVS (FREEPIK)