Recombination Calculations by Branch Diagrams


William D. Gilliland and Michael G. Rosenbaum

This is a method for analyzing recombination events in laboratories focused on genetic recombination. As the authors note, genetic recombination can be difficult to understand because of the abstract nature of the experiments used to measure it.  Thus, this resource demonstrates how to use branch diagrams to list all possible phenotypes for the progeny and identify which classes are recombinant, calculate the expected phenotype frequencies from known map distances, and use progeny count data to calculate map distances and interference. The branch diagram method provides visual cues for which classes are recombinant, as well as a structural guide to assist students with the mathematical analysis of recombination data.

Genetics Concept(s) Addressed:

Nature of genetic material: What are the molecular components and mechanisms necessary to preserve and duplicate an organism’s genome?
Transmission/patterns of inheritance: How does the phenomenon of linkage affect the assortment of alleles during recombination?
Core Competencies Addressed:

Students should be able to implement observational strategies to devise a question.

Students should be able to generate testable hypotheses.

Students should be able to design an experiment using appropriate controls and appropriate sample sizes.

Students should be able to gather and evaluate experimental evidence, including qualitative and quantitative data.

Students should be able to apply statistical methods when analyzing their data, and use patterns to construct a model.


Intermediate undergraduate; biology/genetics majors
Activity Type:

Laboratory protocol
Activity Length:



Gilliland, William D. and Rosenbaum, Michael G. (2013). Recombination Calculations by Branch Diagrams. Genetics Society of America Peer-Reviewed Education Portal (GSA PREP): 2013.002; doi: 10.1534/gsaprep.2013.002

Laboratory Justification and Description for Instructors

Supplemental Material:

Blank Worksheets:

2-marker Branch Diagram Worksheet

3-marker Branch Diagram Worksheet

4-marker Branch Diagram Worksheet

Sample Data Sets