A comprehensive simulation package, with 40 exercises that reinforce the principles of:
Homozygous/heterozygous genotypes
Dominance and no dominance
Comparing observed and expected ratios
Genetic notation for linked and unlinked loci
Estimating recombination and drawing genetic maps

A feature of the program is that it allows gene symbols to be shown or hidden, and allows trials in which students can work out the principles with gene symbols shown and then test themselves with symbols hidden. All exercises can be computer marked, and hand marking is facilitated in the more advanced exercises where it is desirable for students to hand in reports.

Here's an example of one exercise. It involves a cross between two plants:



The description of the exercise assumes that you know some of the terms of genetics, 'heterozygote' and 'genotype'.

At first it is not obvious what is happening. All the plants look the same. But you can generate more offspring simply by dragging plants out of the box, after which another one is produced. After you have repeated this process several times, the following occurs:


Now it becomes clear what is going on. Blue petals are 'recessive' to red. You are ready to answer the first question:


You answer the question simply by clicking on the individual which is 'homozygous' for the blue gene:


You are correct!


But now comes a question that is much harder.


Can this be done? Since the red gene is dominant, the heterozygote and homozygote for the red gene will look the same. One way out, as the exercise description says, is to just look at the underlying genotypes when you need to. The program allows you to look at genotypes, and to edit gene symbols:


When you click on OK, the following is shown:


so that it is now obvious which are the homozygotes and which the heterozygotes.

This problem could have been solved without asking for the genotypes. If you had testcrossed the red plants, by crossing to the blue plant, you would eventually find one which did not give blue offspring, and therefore must have been homozygous for red.

If you want to set a problem in which the student does not get the opportunity to shortcut the exercise by looking at the genotypes, how would you do it? The following screen shows the basis for the exercise we have just looked at:


Every aspect of the exercise is set from this screen. It specifies that there will be a single locus segregating, that there will be two parents that are both heterozygous. The 'Show genotypes' line indicates that genotypes are available, but hidden initially. This line could easily have been changed to hide genotypes.

One other screen is available which controls various parameters of the overall simulation:


It controls whether exercises are elementary or advanced, sets the degree of automation, nominates whether the exercises are graded by the computer or not, and sets various other parameters of the simulation. It makes Mendelsim into a truly general program for genetic simulation in a learning context.