Dominant and recessive
One copy of T is enough.
Two copies, one trait
A pea plant has two copies of the gene for height. A copy can be T, which makes plants tall, or t, which makes plants short.
A plant has one T copy and one t copy. What will it look like?
What this lesson covers
The idea
A trait whose single copy is enough for it to be expressed is dominant (TT and Tt both show T); a trait expressed only when both copies are alike, as in tt, is recessive.
Two copies, one trait
A pea plant has two copies of the gene for height. A copy can be T, which makes plants tall, or t, which makes plants short.
A plant has one T copy and one t copy. What will it look like?
- Tall
- Short
- Medium height
Choose the copies
Set the two copies and look at the plant.
One T is enough
TT and Tt plants were both tall. Only tt was short. So a single copy of T is enough, but short needs both copies to be t.
A trait whose single copy is enough for it to be expressed is dominant: TT and Tt both show T. A trait that is expressed only when both copies are alike, as in tt, is recessive.
- Copies | Plant
- TT | tall
- Tt | tall
- tt | short
Notes
A trait expressed from a single copy is dominant (TT and Tt show T). A trait expressed only when both copies are alike, as in tt, is recessive.
Check yourself
What are plants with the copies TT and Tt like?
Which pair of copies makes a short plant?
Why is T called a dominant trait?
A trait expressed only when both copies are alike, as in tt, is called…
- TT is tall and Tt is of medium height. There are no halfway characteristics. A single copy of T is enough to make the plant tall.
- Both are tall — correct. Yes!
- TT is tall and Tt is short. In Tt a single copy of T is enough to make the plant tall.
- Tt. In Tt, a single copy of T is enough to make the plant tall.
- TT. TT is a tall plant. Both copies have to be t for a plant to be short.
- tt — correct. Yes!
- A single copy of it is enough for the trait to be expressed — correct. Yes!
- It needs both copies to be expressed. That describes a recessive trait such as t, which is expressed only when both copies are alike.
- It is hidden when the other copy is t. In Tt the plant is tall, so T is expressed even when the other copy is t.
- dominant. A dominant trait is expressed with just a single copy.
- recessive — correct. Yes!
- F1. F1 names the first generation of progeny. It is not a kind of trait.