Phylogeny in AP Biology Full Review

Phylogeny in AP Biology

Phylogeny is the study of evolutionary relationships among species, a fundamental concept in AP Biology. It explains how organisms are related through common ancestry and how we classify life using phylogenetic trees and cladistics. This guide breaks down everything you need to know about phylogeny for the AP Biology test, including molecular evidence, taxonomy, and how to interpret phylogenetic trees.

1. What Is Phylogeny?

Phylogeny refers to the evolutionary history of a species or group of organisms. Scientists use DNA, morphology, and fossil records to determine how species are related.

Key Points:

Common Ancestors: Organisms with a shared evolutionary history come from a common ancestor.
Phylogenetic Trees: Diagrams that show evolutionary relationships.
Cladistics: A method of classifying species based on shared derived traits.

2. Phylogenetic Trees: Structure and Interpretation

A phylogenetic tree (or evolutionary tree) visually represents relationships between species.

Key Features:

Branches: Represent evolutionary lineages.
Nodes: Indicate a common ancestor.
Clades: A group of organisms that includes an ancestor and all its descendants.

💡 Tip for the AP Exam: If two species share a recent common ancestor, they are more closely related than species with a distant ancestor.

3. Cladistics and Shared Traits

Cladistics is a system of classification that groups organisms based on shared derived characteristics (traits that evolved in a common ancestor but not in earlier ancestors).

Key Terms:

Monophyletic Group (Clade): Includes a common ancestor and all its descendants.
Paraphyletic Group: Includes a common ancestor but not all descendants.
Polyphyletic Group: Includes species with similar traits but different ancestors.

4. Molecular Evidence in Phylogeny

DNA and protein comparisons provide strong molecular evidence for evolutionary relationships. Scientists use:

Mitochondrial DNA (mtDNA): Useful for tracing ancestry over recent timescales.
Ribosomal RNA (rRNA): Used for studying ancient evolutionary relationships.
Molecular Clocks: Estimate when species diverged by analyzing mutations in DNA.

💡 AP Exam Tip: The more similar the DNA sequences of two species, the more closely related they are.

5. Taxonomy and the Classification of Life

Taxonomy is the system of naming and classifying organisms based on phylogenetic relationships. The hierarchical system is:

Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species

(🔑 Mnemonic: “Dear King Philip Came Over For Good Soup”)

The three domains of life are:

Bacteria: Prokaryotic, unicellular organisms.
Archaea: Extremophiles with unique biochemistry.
Eukarya: Includes protists, fungi, plants, and animals.

6. Practice Questions for the AP Biology Test

What is the difference between a monophyletic, paraphyletic, and polyphyletic group?
How do molecular clocks help scientists estimate evolutionary relationships?
Explain how a phylogenetic tree shows the evolutionary history of species.

Ace Your AP Biology Test with Phylogeny Knowledge!

Understanding phylogeny is essential for AP Biology success. Mastering phylogenetic trees, cladistics, molecular evidence, and taxonomy will help you answer key exam questions confidently.

More for you about Phylogeny

1. Phylogenetic Trees and Cladograms

Phylogenetic Trees: Diagrams that show the evolutionary relationships among species, including the timing of evolutionary events (branch lengths may represent time or genetic divergence).
Cladograms: Simplified diagrams that show patterns of shared ancestry but do not necessarily indicate evolutionary time or the degree of genetic change.
Nodes: Points on a tree where branches split, representing common ancestors.
Branches: Lines that connect nodes, showing evolutionary lineages.
Clades: Groups of organisms that include a common ancestor and all its descendants (monophyletic groups).

2. Evidence for Phylogeny

Morphological Evidence: Physical traits (e.g., bone structure, leaf shape) used to infer relationships.
Molecular Evidence: DNA, RNA, and protein sequences provide more precise data for constructing phylogenies.
Fossil Evidence: Fossils help trace the history of life and provide information about extinct species and their relationships.

3. Shared Characteristics

Homologous Structures: Features shared by different species due to common ancestry (e.g., the forelimbs of humans, bats, and whales).
Analogous Structures: Features that serve similar functions but evolved independently (e.g., wings of birds and insects).
Vestigial Structures: Remnants of structures that were functional in ancestors but have lost their function over time (e.g., human appendix).

4. Molecular Clocks

Molecular clocks use the rate of mutation in DNA sequences to estimate the time of divergence between species.
Assumes that mutations accumulate at a relatively constant rate over time.

5. Types of Groups

Monophyletic Group (Clade): Includes a common ancestor and all its descendants.
Paraphyletic Group: Includes a common ancestor and some, but not all, of its descendants.
Polyphyletic Group: Includes species from different evolutionary lineages without a common ancestor.

6. Applications of Phylogeny

Understanding evolutionary history and biodiversity.
Tracing the origin of diseases (e.g., HIV, COVID-19).
Informing conservation efforts by identifying evolutionary distinct species.

7. Constructing Phylogenies

Outgroup: A species or group closely related to but not part of the group being studied, used to root the tree.
Parsimony: The principle that the simplest explanation (fewest evolutionary changes) is most likely correct.

8. Key Terms

Speciation: The formation of new species through evolutionary processes.
Divergence: The accumulation of differences between groups leading to the formation of new species.
Convergent Evolution: Independent evolution of similar features in unrelated lineages (e.g., wings in bats and birds).

Example Question

Q: Based on the phylogenetic tree below, which two species are most closely related?

  A
 / \
B   C
   / \
  D   E

A: Species D and E are most closely related because they share the most recent common ancestor.

Study AP Biology

Practice Digital SAT

Find us on Facebook