Skip to main content
Pearson+ LogoPearson+ Logo
Ch. 25 - Phylogenies and the History of Life
All textbooksFreeman 8th EditionCh. 25 - Phylogenies and the History of LifeProblem 6
Chapter 24, Problem 6

You can use a 'one-snip test' to identify monophyletic groups—meaning that if you 'cut' any branch on a tree, everything that 'falls off' is a monophyletic group. Why is this valid?

Verified step by step guidance
1
Understand the concept of a monophyletic group, which includes an ancestor and all of its descendants. This group shares a common evolutionary history and unique genetic traits that distinguish them from other organisms.
Visualize the phylogenetic tree, where each branch represents a lineage and each node represents a common ancestor. The entire tree is a graphical representation of evolutionary relationships.
Recognize that cutting a branch on the phylogenetic tree isolates a segment of the tree. This segment represents a common ancestor and all its descendants, which is the definition of a monophyletic group.
Realize that the 'one-snip test' is valid because it ensures that all organisms in the isolated segment share a most recent common ancestor, without including any organisms that do not share this ancestor. This is the essence of a monophyletic group.
Apply this understanding to identify monophyletic groups in any phylogenetic tree by imagining or drawing a single cut that would isolate a group of organisms along with their common ancestor.

Verified Solution

Video duration:
1m
This video solution was recommended by our tutors as helpful for the problem above.
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Monophyletic Groups

Monophyletic groups, or clades, consist of an ancestor and all its descendants. This concept is fundamental in phylogenetics, as it helps classify organisms based on shared evolutionary history. Identifying monophyletic groups allows scientists to understand evolutionary relationships and the lineage of species.
Recommended video:
06:37
Monophyletic, Paraphyletic, & Polyphyletic Group

Phylogenetic Trees

Phylogenetic trees are diagrams that represent evolutionary relationships among various biological species based on similarities and differences in their physical or genetic characteristics. Each branch point represents a common ancestor, and the structure of the tree illustrates how species diverged over time, making it a crucial tool for visualizing monophyletic groups.
Recommended video:
04:13
Building Phylogenetic Trees Example 2

One-Snip Test

The one-snip test is a method used to determine if a group of organisms is monophyletic by 'cutting' a branch on a phylogenetic tree. If all the organisms that fall off the branch share a common ancestor and include all descendants, the group is monophyletic. This test is a practical way to assess the validity of taxonomic classifications.
Recommended video:
Guided course
03:02
Test Crosses
Related Practice
Textbook Question

Which of the following best characterizes an adaptive radiation? a. Descendant species occupy a large geographic area. b. A single lineage diversifies rapidly, and descendant species occupy many habitats and ecological roles. c. Natural selection is particularly intense, because disruptive selection occurs. d. Species recover after a mass extinction.

410
views
Textbook Question

Which of the following is an example of homoplasy? a. hair in humans and fur in mice b. astragalus ankle bones in hippos and deer c. Hox genes in humans and flies d. streamlined bodies in dolphins and ichthyosaurs

660
views
Textbook Question

What important assumption does parsimony make when assessing which phylogenetic tree is most accurate? Why was parsimony misleading in the case of the astragalus during the evolution of artiodactyls?

449
views
Open Question

Describe one similarity between the End-Cretaceous Extinction and the Sixth Mass Extinction, and one difference.

65
views
Textbook Question

Use the fossil evidence shown in Figure 25.6 to determine whether flight evolved earlier in insects or in birds. Is flight an example of homology or convergent evolution? Explain.

344
views
Textbook Question

Coral reefs are biodiverse ecosystems that provide food, income, coastal protection, and many other services to millions of people. Yet coral reefs are under threat from human impacts such as climate change—many corals cannot tolerate the warming ocean water and have suffered massive 'bleaching' events, which can be fatal. Researchers have discovered that some corals have the capacity to acclimatize to warmer water, while other corals do not. The researchers fear that because corals are long-lived colonial animals and thus evolve slowly, they may not be able to adapt to global warming fast enough to avoid extinction. Explain how the difference between acclimatize and adapt is important to the fate of corals.

384
views