Gene Linkage 2.
Drosophila Experiments on Gene Linkage
Use an online fly lab to repeat some of the experiments which helped Thomas Hunt Morgan in the discovery of linked genes, and the recognition of the role of chromosomes. Students learn that sometimes alleles are not independently assorted. Drosophila eye colour is one example. The connection between parent phenotypes, F1 phenotypes and recombinant genotypes is illustrated using historical experiments. Linkage notation is also introduced.
Explain this prediction, “The association of chromosomes in pairs and their subsequent separation during [meiosis] may constitute the physical basis of the Mendelian law of heredity.” Sutton, W. S. 1902.
Why did it take Thomas Hunt Morgan eight years before he could prove this with a genetic breeding experiment?
Activity 1 Experiments on Drosophila
This is a step by step guide to the activity on the Drosophila experiments of Thomas hunt Morgan.
Use this short presentation to guide students in the experiments on the worksheet.
Use this online simulation to carry out the experiments
Keep a record of the results of the simulation experiments on The discovery of linked genes - Morgan 1910 worksheet below. Answer the questions on the worksheet. Does the data you collect support the idea that inheritance of sex and of other genetic traits depends on the chromosomes?
Activity 2 Extra reading about linkage notation.
If this is the first time students have seen this notation then the following slides will be some help:
These six slides explain clearly how the genes for some characteristics of Drosophila are linked to others
Activity 3 Further online breeding experiments with Drosophila flies
This is a more advanced online Drosophila breeding lab. Use it to find out about Drosophila traits and other Drosophila experiments. The computer calculated chi squared values are nice too.
This is a video introduction.
This is the simulation itself. Click the link.
This activity is designed to help students develop the skill of using chi squared tests of goodness of fit to evaluate whether evidence from genetic experiments actually supports an hypothesis or not.
Students will also learn to predict phenotype ratios, recombinant phenotypes, parental phenotypes and to identify gene linkage when it appears in data from di-hybrid genetics experiments.
The introductory powerpoint is designed to be projected by the teacher while students follow the worksheet which explains how to make predictions and how to test the results. Details of using the simulations for the breeding experiments are outlined in the powerpoint.
The worksheet outlines the story of genetic experiments carried out on Drosophila flies over 17 years by Thomas hunt Morgan in the USA. He was the first to find conclusive experimental proof of gene linkage and later went on to map the positions of genes on chromosomes before winning the Nobel Prize. There are points worth making here about International Mindedness and the nature of scientific discovery.
The Drosophila simulations in activity 2 will give a useful extension for faster students.
There is a wide range of Drosophila activities possible in this animation.
I'm working on some model answers which can be seen on this page: Gene linkage 2 - model answers