Recombination Mapping

By A.K. Matai

Recombination mapping is used to determine if two genes are linked (recombination frequency <50%) or unlinked (recombination frequency ~50%). The distance between two genes is measure in either map units (mu) or centiMorgans (cM).

Recombination Frequency Formula

Recombination Frequency 1

Sample Recombination Mapping Problem

Gene B for body color (black is completely dominant to yellow) and Gene W for wing shape (straight wings are completely dominant to curved wings) are on the same chromosomes. If true breeding yellow fly is crossed to a true breeding curved wing fly to create heterozygous F1 progeny that is test crossed, the following phenotypic ratios are observed among the F2 progeny.

Phenotype Numbers
black body & straight wings 17
yellow body & curved wings 12
black body & curved wings 337
yellow body & straight wings 364

Calculate the distance between the two genes.


First, draw out a schematic detailing the all of the crosses. Then, determine which progeny are parents and recombinants.


Insert the numbers into the recombination frequency formula and calculate away!

 Recombination Mapping 1

Questions, Comments or Concerns?

Feel free to post a your questions, comments or concerns down below!


Locke, John; Deyholos, Michael; Harrington, Michael; Canham, Lindsay; Kang, Min, “Open Genetics Lectures (OGL) Fall 2016”

Donar Reiskoffer. Antique map of Leo Belgicus by Visscher C.J. 2011 Web. 19 Mar. 2017.


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