F1 and F2
Mendel's first crosses.
Tall and short peas
Mendel crossed a tall pea plant with a short pea plant. He looked at the first generation of plants that grew.
What do you expect the plants of this first generation to look like?
What this lesson covers
The idea
Crossing plants with contrasting traits gives F1 progeny showing only one parental trait, with no halfway characteristics; in the F2 from self-pollinated F1 plants, one quarter show the other trait, so both traits were inherited.
Tall and short peas
Mendel crossed a tall pea plant with a short pea plant. He looked at the first generation of plants that grew.
What do you expect the plants of this first generation to look like?
- All tall
- All of medium height
- Half tall and half short
Two generations
Press Next step.
A trait that hides
The F1 plants were all tall, so only one parental trait was seen, not a mixture. Yet when F1 plants self-pollinated, short plants came back in F2. The shortness trait had been inherited, but it was not expressed.
On crossing plants with contrasting traits, the F1 progeny show only one parental trait, with no halfway characteristics. In the F2 from self-pollinated F1 plants, one quarter show the other trait, so both traits were inherited.
Notes
Crossing plants with contrasting traits: F1 shows one parental trait, no mixture. In F2, one quarter show the other trait, so both traits were inherited.
Check yourself
What did the F1 plants of the tall and short cross look like?
One quarter of the F2 plants are short. If there are 400 F2 plants, how many are short?
Answer: 100
One quarter of 400 is 400 divided by 4, which is 100.
Short plants appeared in F2. What does this show?
- All were tall, and none was of medium height — correct. Yes!
- They were of medium height, a mixture of tall and short. There were no halfway characteristics in the F1 generation.
- Half were tall and half were short. All the F1 plants were tall. Only one of the parental traits was seen.
- The F1 plants were a mixture of tall and short. The F1 plants were all tall, with no halfway characteristics. The shortness trait was inherited but not expressed.
- Both the tallness and shortness traits were inherited in the F1 plants, but only tallness was expressed — correct. Yes!
- The shortness trait was lost in F1 and then created again. The shortness trait was still inherited in the F1 plants. It was not expressed, so the plants looked tall.