Hi! Before going into the next lesson, let's recap what we've learn in the past 2 lessons. Try to fill in the keywords that are missing below. If you really have trouble, use your mouse cursor to highlight the blank space where the answer should be, and it should be visible.

Let's Go!

In the past lessons, we saw that children look like their parents because they inherit, or get many of their features from their parents. These features are known as traits. This 'getting' of traits from your parents is called:

[Heredity] <-- Highlight Here for the answer

We also learned that people have been studying Heredity for a long time. The first man to discover Heredity was an Austrian monk who lived in the 19th Century (1800s) called:

[Gregor Mendel]

This man planted a special plant as part of an experiment. He did this experiment to see whether the adult plant would pass tall or short height traits to its seedlings. This plant was a :

[Pea Plant]

Mendel discovered, through his experiment, that the tall and short plants produced seedlings in a peculiar way. Sometime, all the new plants were tall, sometimes, one was short. Mendel, was confused. However, he was also a brilliant scientist and quickly thought of an explanation for this......

We know that Mendel did a very confusing experiment, because some pea plants happened to be tall and some happened to be short.

However, he was also a outstanding scientist and was able to explain why this happened.

Mendel observed that although he cross bred a tall plant and a short plant, only tall plants were produced, and what made the plants short seemed to disappear. .

However, these short plants appeared again when 2 tall plants were cross bred, and for every 3 tall plants, there was 1 short plant.

Mendel came up with an explanation for this strange happening....

He said that each cell that makes up a plant contains 2 special genes (Find out more about Cells and Genes here) . These special genes control whether the pea plants are tall or short. Mendel used the capital letter T to represent the tall gene, and the small letter t to represent the short pea plant.

The baby pea plants in the first breeding were bred from a tall plant AND a short plant. Therefore, they have both tall genes(T) from the tall parent plant, and short genes(t) from the short parent plants, and thus they since they have 2 genes to control height, they have the genes (Tt)

Therefore, new pea plant seedling contains two genes, one that makes it tall and one makes it short. However, these 2 genes don’t mix, the tall gene manages to "block" out the effect of the short gene. Because of the blocking out of the short gene, the plant is still tall.

Still don't understand what happens when a plant has both tall(T) ans short(t) genes. Play the animation below!

Mendel thus called the tall gene the dominant gene, because it was more "powerful" and blocked and dominated and took control, making the plant tall. The short gene that was being blocked out was called the recessive gene, because it took a back seat and was block out by the tall gene.

Therefore, as long as there is a dominant gene (more "powerful" gene), that gene will control a person's traits. For example, in eye colour, the brown eye gene is a dominant gene, and if a person's father has brown eyes and his mother has blue eyes, both will be passed to the baby, but the brown eyes will "block" out the blue eyes, and the baby's eyes will be brown.

However, as you observed from the experiment, and by looking at people around you everyday, the recessive genes that are supposed to be blocked out still appear. There are still people with blue eyes, and Mendel still managed to get 1 short plant. How did this happen?

A plant is short only when there are no dominant tall or brown eye genes. If plants get 2 (t) genes, they don't have any dominant (T) genes, and therfore they become short, since the (t) gene makes them short.

Okay, that was a lot for now. Let's take a break. You can go take a Quiz to see how much you know, and also be sure to look at the side lesson on DNA and Genes if you aren't sure. When you're ready, go on to Part 2

Lesson 3 : Part 2