Brother Gregory and Pea
It is spring in Brno, so Brother Gregory and Brother Joseph want you to help them plant their pea seeds and carry out more investigations into Plant Hybridization.

At the start of each investigation they will ask you a question or questions. To find the answers, you must take two of their pea plants and carry out a series of carefully controlled experiments. In these experiments the plants you choose become the parents of a set of offspring. From the pattern of inheritance seen in these offspring pea plants, you will be able to find the answers you need.

At the start of a genetic cross, the female egg cells of one plant are fertilized with the male pollen from the other plant. Tiny embryos develop, which are nourished with starchy food reserves, these are the seeds (or peas) that will grow into the next generation of pea plants.

You must collect the seeds produced from these genetic crosses, plant them in the ground, wait until they grow and then count the number and type of offspring that you find in the monastery garden.

From the results you obtain Brother Gregory needs to know what you think about his latest theory of inheritance.


Tools of the Trade

A typical genetic cross, as devised by Gregor Mendel, is carried out in three phases, all of which are available to you using the Plant Hybridization simulation.

Phase One:
Choose the Characteristics

- Small, well defined and distinct parts of the phenotype of the plant, known today as traits, were originally selected by Brother Gregory because they were easily seen and were unambiguous.

He has picked out three pairs of traits for you to use; these are

  • Height trait - plants are either tall or short.

  • Flower Color trait - plants have either purple flowers or white flowers.

  • Pod Color trait - the seed pods are either green or yellow.

Any parent plant can have any one (or any two) of the above three traits. For example, a plant can have green pods and a short height, while another plant might have purple flowers and yellow pods.

However, the same plant cannot have both options for the same trait. For example, a single plant cannot show both purple and white flowers, or tall height and short height.

The simulation will ignore any attempt to force a parent plant to show both options of any particular trait.

now do this At the start of every genetic cross experiment you must choose at least one option for at least one trait for each parent. You do this by first clicking on one of the "radio" buttons in the "Traits" menu. You then click on either of the larger panels under the "Parent One" or "Parent Two" headings. The option for the trait you have chosen will appear in the box.

Phase Two:
Collect the Seeds

When Brother Gregory carries out this part of the experiment, he carefully collects the pollen grains from the flower of one plant onto the tip of a small paint brush. He then dusts this pollen onto the female structures within the flower of a different plant.

He knows that to get an new plant embryo there must be a contribution from two parents, one male (pollen) and one female (an egg cell), but he is not sure what this contribution is, or what it does.

After the pollen has fertilized the egg cell, the resulting zygote (which is the cell that results from the fusion of the male and female contributions) begins to divide and develop into a new, tiny embryo.

Shortly the embryo stops growing, and is surrounded by a starchy reservoir of food. It is the combination of embryo and food reserves that we call a seed and which, when planted in the ground, has the potential to grow and develop into a completely new plant.

now do this The simulation carries out this part of the genetic cross for you. All you have to do is click on the button called "Collect seeds".

Phase Three:
Plant Seeds and See the Results
- Once the seeds are in the ground their embryos begin to grow again. Acting under the genetic instructions they received from their parents, the new plants produce roots, stems, leaves, flowers and eventually more seeds in pods.

Brother Gregory has found that he can learn a lot about the inheritance mechanism but observing and counting the phenotypes that appear in the new, first filial or F1 generation of Pisum plants.

now do this The simulation will give you both the numbers and type of offspring that can occur from your chosen genetic cross. You must write down and record exactly what you did and what kind of result you saw. These quantitative and qualitative observations are the data on which you will base your conclusions and use to deduce the answers to Brother Gregory's questions.


Science at a Distance
© 1999 Professor John Blamire