From Seed to Seed:
Plant Science for K-8 Educators

The Role of Chance

Now we come to a key point in the study of genetics: The way that the chromosomes segregate during meiosis is entirely random. It is impossible to predict which genes will migrate to which cells.

OR

These are the possible combinations of chromosomes in the spores. Because the spores divide by mitosis, these combinations will be passed down to the daughter cells, the gametes.

Remember that the production of egg and sperm takes place in different parts of the plant body, so each can have any one of the combinations above. Now suppose fertilization takes place, and egg and sperm are united. Again, chance plays a role.

Which particular egg and which particular sperm unite during fertilization is also entirely random.

There is no way to predict which reproductive cells will unite.

There are nine possible combinations of chromosomes in a zygote resulting from union of any two of these eggs and sperm. Here are the nine, along with which expression of the traits they'll exhibit:

You can see that eight out of the nine will express one or both dominant traits. Which of the combinations of genes results in a plant that exhibits the recessive traits, green seeds and wrinkled seed coat? Only the last one, yyrr.