Discovering Genetics

Recap
As always, we need to recap what we've learnt in Part 1 of Lesson 3 : From his pea plant experiment, Mendel said that 2 [genes] controlled height of the pea plants. These two genes were obtained from the parent plants. The controlling or more "powerful" gene that blocked out the other, laid back, recessive gene was the [dominant] gene. Mendel called gave this particular gene the symbol (T), and gave the recessive gene the symbol (t). For any plant to be tall, it must have a (T) gene. A tall plant can have the combination of (Tt) or (TT), because as long as it has the (T) gene, it is tall. A short plant can only have the combination of (tt). If there are any (T) genes, the plant becomes a tall plant. In the experiment, when one of the parent plants was tall, it contained a gene combination of (Tt). However, it remained tall because the (T) gene was dominant over the (t) gene. When one of the parent plants was short it contained a gene combination of (tt). so that there was no dominant gene to block it.

Recap

As always, we need to recap what we've learnt in Part 1 of Lesson 3 :

From his pea plant experiment, Mendel said that 2 [genes] controlled height of the pea plants. These two genes were obtained from the parent plants. The controlling or more "powerful" gene that blocked out the other, laid back, recessive gene was the

[dominant] gene.

Mendel called gave this particular gene the symbol (T), and gave the recessive gene the symbol (t).

For any plant to be tall, it must have a (T) gene. A tall plant can have the combination of (Tt) or (TT), because as long as it has the (T) gene, it is tall.

A short plant can only have the combination of (tt). If there are any (T) genes, the plant becomes a tall plant.

In the experiment, when one of the parent plants was tall, it contained a gene combination of (Tt). However, it remained tall because the (T) gene was dominant over the (t) gene. When one of the parent plants was short it contained a gene combination of (tt). so that there was no dominant gene to block it.

Lesson 3 - The Third Stage : Part 2 - The Punnett Square - The ratio of tall to short
Let's look back at the pea plant experiment. In the end, Mendel got 3 tall plants and 1 short plant, even though he bred two tall plants. However, as we learned before, some tall plants have the genes (Tt). They also have the (t) gene to make them short, but this doesn't do its job becaus it is blocked by the dominant gene, which makes it tall, the (T) gene. Tall plants can also have the gene combination (TT), where there are no short genes to block out at all. Sometime after Mendel's discovery, another man, called Reginald Punnet discovered an easy way to explain the complicated experiment with the pea plants. He used a diagram called the Punnett Square. The Punnett Square was able to explain why Mendel's experiment happened the way it did. Click below to see how the Punnett Square explained the first part of the experiment. After the first breeding of the tall and short parent plants, all four seedlings were tall. These tall plants contained the genes (Tt), because they got one tall gene from the tall parent plant and one short plant form the short parent plant. However. in the second stage, what happens, and why do only 3 tall plants appear and 1 short one? Let's find out... Summing Up Therefore, the Punnett Square was able to explain why the pea plants grew in such a way in Mendel's experiment. When Mendel first planted the tall and short pea plant, they had the genes (TT) for the tall plant and (tt). (TT) is a tall plant because both (T) genes are dominant, and don't need to block out anything, and automatically make the plant tall. (tt) is a short plant because there are no (T) genes. Because there are no (T) genes to block out the (t), the (t) gene takes effect and makes the plant short. In the Punnett Square, a parent plant gives 1 of its genes, either (T) or (t) to each four plants. The other parent then also gives 1 of the genes. In the first part, the genes were either (TT) or (tt), so each (TT) gene from the parent gave a (T) and the (tt) gene gave (t), because they had no other gene. The plants that formed got one (T) from the (TT) parent, and one (t) from the (tt) parent, and became (Tt). Howeverm because (T) is the dominant gene, it blocks out (t) even though they both exist in the same cell. However, when two of these (Tt) plants breed, they can give a (T) or (t) because they have both, although the (t) is blocked out. Two parents with (Tt) can give their genes in a way that it produces the genes (TT), (Tt) and (tt) by combining differently, and thus the plant with (tt) remained short and a short plant appeared in the second breeding. Okay, that's all for now. Next Lesson we look at the uses of Genetics in out daily life. Please drop us a mail if you have any questions at our contact page.

Lesson 3 - The Third Stage : Part 2 - The Punnett Square - The ratio of tall to short

Let's look back at the pea plant experiment. In the end, Mendel got 3 tall plants and 1 short plant, even though he bred two tall plants. However, as we learned before, some tall plants have the genes (Tt). They also have the (t) gene to make them short, but this doesn't do its job becaus it is blocked by the dominant gene, which makes it tall, the (T) gene. Tall plants can also have the gene combination (TT), where there are no short genes to block out at all.

Sometime after Mendel's discovery, another man, called Reginald Punnet discovered an easy way to explain the complicated experiment with the pea plants. He used a diagram called the Punnett Square.

The Punnett Square was able to explain why Mendel's experiment happened the way it did. Click below to see how the Punnett Square explained the first part of the experiment.

After the first breeding of the tall and short parent plants, all four seedlings were tall. These tall plants contained the genes (Tt), because they got one tall gene from the tall parent plant and one short plant form the short parent plant.

However. in the second stage, what happens, and why do only 3 tall plants appear and 1 short one? Let's find out...

Summing Up

Therefore, the Punnett Square was able to explain why the pea plants grew in such a way in Mendel's experiment. When Mendel first planted the tall and short pea plant, they had the genes (TT) for the tall plant and (tt). (TT) is a tall plant because both (T) genes are dominant, and don't need to block out anything, and automatically make the plant tall. (tt) is a short plant because there are no (T) genes. Because there are no (T) genes to block out the (t), the (t) gene takes effect and makes the plant short.

In the Punnett Square, a parent plant gives 1 of its genes, either (T) or (t) to each four plants. The other parent then also gives 1 of the genes. In the first part, the genes were either (TT) or (tt), so each (TT) gene from the parent gave a (T) and the (tt) gene gave (t), because they had no other gene.

The plants that formed got one (T) from the (TT) parent, and one (t) from the (tt) parent, and became (Tt). Howeverm because (T) is the dominant gene, it blocks out (t) even though they both exist in the same cell.

However, when two of these (Tt) plants breed, they can give a (T) or (t) because they have both, although the (t) is blocked out. Two parents with (Tt) can give their genes in a way that it produces the genes (TT), (Tt) and (tt) by combining differently, and thus the plant with (tt) remained short and a short plant appeared in the second breeding.

Okay, that's all for now. Next Lesson we look at the uses of Genetics in out daily life. Please drop us a mail if you have any questions at our contact page.