Gene distribution during cell division

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

Gene distribution during cell division

Now let's look at how this information relates to what we know about chromosomes and the formation of gametes.

We have already discussed homologous chromosomes. Remember that in most plant cells (all except the reproductive cells), chromosomes occur in pairs. Corresponding chromosomes-the two chromosomes that make up a pair-are described as homologous.

The genes for individual traits are located on homologous chromosomes. Let's look at a simple example of a plant with two chromosome pairs.

We'll stick with peas, and with our red and blue chromosome diagrams. Let's say that the gene for seed color is located on the long, red chromosome. Since the chromosomes occur in pairs, there will be one gene for seed color donated from the egg parent on one chromosome, and one gene for seed color donated from the sperm parent on the other chromosome.

Let's follow the seed coat characteristics as well. Remember, the two options are round and wrinkled. Round is dominant (R), wrinkled is recessive (r). We'll say that the gene for seed coat is located on the blue chromosome. To make things easier, we'll indicate the genes with little coded balls.

Now let's look again at the formation of gametes. Remember that the diploid cell divides to form haploid spores. These spores then divide by mitosis to form haploid gametes.

For this example, we'll begin with a cell that contains one dominant and one recessive gene for each trait: YyRr

There are two possible configurations in the daughter cells after the first cell division of meiosis:

Which configuration will it be, A or B? Let's have a look...

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