What is Recombinant Mapping?

Thomas Hunt Morgan

The work of Thomas Hunt Morgan in 1911 revealed a new understanding of how genes are inherited. His work on Drosophila demonstrated that: (1) traits that were assumed to be ‘linked’, or inherited together, could be unlinked and inherited independently, and (2) some genes demonstrated little, if any, linkage.

The theory of linked genes comes from the presumption that genes located close together in space have a greater probability of being inherited together. To explain his observations, Morgan proposed that ‘crossing over’ events occurred enabling the exchange of genetic information.

Presently, this event is termed ‘recombination’, and known to occur during the prophase stage of meiosis between alleles of homologous chromosomes. This generates different combinations of alleles in each chromosome and the resultant gametes will possess recombinant chromosomes.

In addition to his theory of ‘crossing over’, Morgan further hypothesized that the frequency of recombination events could be estimated according to the distance between two genes on a chromosome. Thus, in the event of ‘crossing over’, two adjacent genes could be unlinked. Morgan correctly stipulated that the relationship between the strength of the genetic linkage between two genes was dependent on the distance between them.

This proposition enabled the construction of the human genome map.

Using Recombination Frequency to Map the Human Genome

The proportion of crossovers occurring between two genes can be used to indicate the distance between them, and thus enable the construction of a genetic map that illustrates how all genes in the genome are related in space.

The earliest experiments performed were by Sturtevant. He performed crosses between two Drosophila flies that possessed two genetic traits. For example, to determine the distance between two genes, vermilion eyes (V) and long wings (L) Sturtevant crossed a Drosophila with these features and with another with rudimentary wings and red eyes.

Image showed the Fruit Fly, Drosophila melanogaster. Photograph from the side showing the head and torso. Image Credit: Ireneusz Waledzik / Shutterstock
Image showed the Fruit Fly, Drosophila melanogaster. Photograph from the side showing the head and torso. Image Credit: Ireneusz Waledzik / Shutterstock

The resultant F1 generation produced offspring with either (1) red eyes and long wings or (2) vermillion eyes and long wings. This generation was subsequently crossed again and noted offspring of this F2 generation that possessed unexpected phenotypes. In total four classes of male offspring were observed in the F2 generation.

Male offspring are only used in the search from recombinants as the additional X chromosome in females can possess dominant genes that obscure the phenotype of the offspring.

  1. Red eyes and long wings
  2. Red eyes and rudimentary wings
  3. Vermillion eyes and long wings
  4. Vermillion eyes and rudimentary wings

Of the four classes of phenotypes observed, only (1) and (4) were expected and could be explained by recombination events. Classes (2) and (3) arose from nonrecombinants. From the frequency of the phenotypes in the F2 generation, the distances between the genes and the order in relation to one another could be determined. This spatial mapping of the genes is referred to as a linkage map. Sturtevant further defined the units of measurements for the linear distances, which he termed the ‘map unit’, presently referred to as the centimorgan (cM).

One centimorgan represented a 1% proportion of recombinants present in the offspring, i.e. a recombination frequency of 0.01.

The recombination frequency is calculated using the following equation:

Deviations from the Expected Recombination Frequency: The Discovery of Interference

Sturtevant discovered that not all recombinant frequencies produced experimentally could be used to produce a map that linearly mapped genes on a chromosome.

In addition, his theorized distances did not match those obtained from those calculated using the recombinant offspring data. This led Sturtevant to hypothesize that if two genes were an appreciable distance apart, instances of double recombination could occur.

He further suggested, based on the discrepancies between the theoretical and calculated recombination frequencies, that one crossover event may inhibit subsequent crossover events in a phenomenon he called ‘interference’.

This conclusion was based on his examination of crossover events between three genes: C (color of the body), EC (two closely-linked genes encoding eye color), and R (rudimentary wings). He found the recombinant frequency that produced a gametic chromosome comprised of B and CO genes from parental chromosome one and R on parental chromosome two was approximately 0.5 or a ratio of 1:2 (CO/R: nonrecombinants. This described the recombinant CO/R.

However, when a crossover occurred to produce an offspring with a chromosome comprised of a B from parental chromosome one and CO and R from parental chromosome two (recombinant B/CO), the likelihood of a second CO/R recombination event dropped (i.e. a ratio of 1:6:5 (CO/R: B/CO: nonrecombinants)) was seen. This demonstrated that the first crossing over event was interfering with the second.

The work of both Morgan and Sturtevant progressed our understanding of inheritance and began the process of gene mapping.

The ability to map genes relies on the principle of crossing over the ability of two genes that are present on the same chromosome to undergo a crossover event is related to the distance between them.

The recombination frequencies can be calculated by studying thousands of offspring. This is the key determinant of linkage distance between genes and can be used to map an entire chromosome rather than defining distances in a physical manner.

Further Reading

Last Updated: Feb 3, 2021

Hidaya Aliouche

Written by

Hidaya Aliouche

Hidaya is a science communications enthusiast who has recently graduated and is embarking on a career in the science and medical copywriting. She has a B.Sc. in Biochemistry from The University of Manchester. She is passionate about writing and is particularly interested in microbiology, immunology, and biochemistry.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Aliouche, Hidaya. (2021, February 03). What is Recombinant Mapping?. AZoLifeSciences. Retrieved on March 04, 2024 from https://www.azolifesciences.com/article/Recombinant-Mapping.aspx.

  • MLA

    Aliouche, Hidaya. "What is Recombinant Mapping?". AZoLifeSciences. 04 March 2024. <https://www.azolifesciences.com/article/Recombinant-Mapping.aspx>.

  • Chicago

    Aliouche, Hidaya. "What is Recombinant Mapping?". AZoLifeSciences. https://www.azolifesciences.com/article/Recombinant-Mapping.aspx. (accessed March 04, 2024).

  • Harvard

    Aliouche, Hidaya. 2021. What is Recombinant Mapping?. AZoLifeSciences, viewed 04 March 2024, https://www.azolifesciences.com/article/Recombinant-Mapping.aspx.


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoLifeSciences.
Post a new comment
Azthena logo

AZoM.com powered by Azthena AI

Your AI Assistant finding answers from trusted AZoM content

Your AI Powered Scientific Assistant

Hi, I'm Azthena, you can trust me to find commercial scientific answers from AZoNetwork.com.

A few things you need to know before we start. Please read and accept to continue.

  • Use of “Azthena” is subject to the terms and conditions of use as set out by OpenAI.
  • Content provided on any AZoNetwork sites are subject to the site Terms & Conditions and Privacy Policy.
  • Large Language Models can make mistakes. Consider checking important information.

Great. Ask your question.

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Uncovering How to Protect Nerves in Neurodegenerative Diseases