Morgan, mutations and flies

It is often the case that scientific progress accelerates dramatically when a group of scientists focuses their attention on a particular problem.

In biology, this often involves the choice of a model organism.  Different model organisms are used to study different problems and processes.

How is it a possible that studying one organism leads to rules that apply to a wide range of organisms? 

The answer is really simple, all organisms on earth are related to one another.  They shared a common ancestor that had most of the major basic molecular processes already in place.

It is this evolutionary unity that makes the use of model systems productive.

Drosophila melanogaster was initially proposed as a model organism for genetic studies in 1901 by W.E. Castle. 

Known by a number of different names, including "fruit fly", "vinegar fly", and "pomace fly", D. melanogaster is easily grown in the lab.

An adult D. melanogaster is about 3 mm in length, and proceeds from conception to sexual maturity in about 2 weeks. 

One female can produce hundreds of offspring from a single mating.

Matings can be set up in small glass vials – hundreds of matings (crosses) can be set up in a very small space.

Beginning in 1910, Thomas Hunt Morgan, a well-known embryologist, began working with D. melanogaster.  

Much these studies were carried out in a 368 square foot room crowded with eight desks, known as the fly room. 


Morgan was joined over the subsequent decades by an inspired group of students and colleagues, including two undergraduates, Calvin Bridges and Alfred Sturtevant.

Male and female Drosophila can be distinguished by a number of traits, including abdomenal pigmentation.

Switch back and forth between male and female (panel to the left, below) to familiarize yourself with the differences -- you will need them when it comes time to sort flies!

images adapted from THE PHYSICAL BASIS OF HEREDITY, Thomas Hunt Morgan Philadelphia: J.B. Lippincott Company 1919.

The essential point in science is not a complicated mathematical formalism or a ritualized experimentation. Rather the heart of science is a kind of shrewd honesty that springs from really wanting to know what the hell is going on! - Saul-Paul Sirag


In 1910, while looking through a vial of flies, Morgan discovered a single white-eyed male; normal or "wild-type" Drosophila have red eyes.

He isolated this individual and found that it was fertile when bred with wild type virgin females.

Experiment 3: Characterization of the white-eye phenotype.   You have in your lab the original white eyed male, and normal, red eyed females. Design a series of crosses that will determine whether white eye behaves like a typical mendelian trait.

  • Use javaGenetics to carry out your crosses; describe the phenotypes that you observe.  Does white-eye behave as a dominant or recessive trait? 
  • In your report, include the crosses your carried out, as well as your observations

Use Wikipedia to look up concepts | revised 10-Dec-2005