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EXPERIMENTAL SET UP AND BACKGROUND INFORMATION

Now that students have established the following principles, we took a look at the data from CGS #1.

Offspring get half of their genetic information from each parent
All plants have two pieces of genetic information that determine a certain trait (bud shape, leaf shape, flower color, etc...)

The crosses we did in CGS#1 were:

Pointed x Pointed
Pointed x Rounded
Rounded x Rounded

OBSERVATIONS / DATA

Although we collected large amounts of data (students did five of each cross), the compiled data is what is shown below:

Pointed x pointed produced one outcome
- All of the offspring were pointed

Pointed and rounded produced two outcomes
- All offspring were rounded

- Half the plants were rounded and half were pointed

Rounded and rounded also produced two outcomes
- All plants were rounded

- 75% were rounded and 25% were pointed

EXPERIMENTAL SET UP AND BACKGROUND INFORMATION

We had students focus on the following crosses and in the following crosses and in the following order:

Plants with pointed leaves x plants with pointed leaves = all offspring with pointed leaves.
Plants with rounded leaves x plants with rounded leaves = 3/4 offspring with rounded leaves and 1/4 with pointed leaves.

Back To CGS 1

PROCEDURE:

Using the principles established (the science students developed) try to explain how two rounded plants can produce pointed plants?

Remember:

All offspring get half their genetic information from each parent.

Each individual plant has two pieces of genetic information that determine a particular trait (bud shape in this case)

Discussion

Question

If both of the parents have rounded leaves, then how could they produce a pointed offspring?

This question led to the idea that the parents must have pointed genetic information, otherwise there would be no way to explain where the pointed plants came from.

However, they must also have rounded genetic information, otherwise there would be no way to explain why the parents have rounded leaves.

Question:

If the plant with the rounded and pointed genetic information (Rp) has both then why does it look rounded?

The idea proposed was when rounded is with pointed, rounded genetic information "overrides" the pointed information. In other words, whenever rounded genetic information (R) is with pointed genetic information (p), then (R) determines the bud shape and (p) does not, even though it must be present.

The scientific term for this is dominant. In other words, the (R) is dominant genetic information because it controls what the plant's buds look like, even though the (p) genetic information is there.

The genetic information that is there but does not control what the plant's buds look like (p) is called recessive

When (R) genetic information is with (p) genetic information, the (R) determines the bud shape.

This means the the plant with pointed buds must have genetic information that does not contain (R), otherwise it would look rounded like the parents. Thus, its genetic information must be (pp).

And, finally if the pointed plant gets half its genetic information from each parent, then both parents must have (p) genetic information for the offspring to have (pp) genetic information.