Two traits at once

The idea

When plants differing in two traits are crossed, the F1 show both dominant traits, while the F2 include new combinations of traits, showing that different traits are inherited independently.

Height and seed shape

Mendel crossed a tall plant with round seeds and a short plant with wrinkled seeds. The F1 plants are all tall with round seeds. Then the F1 plants self-pollinate to give F2.

Which kinds of plants might he find in F2?

• Some with new combinations, such as tall with wrinkled seeds
• Plants exactly like the F1 plants
• Plants exactly like the two original parents

Follow the cross

Press Next step.

Traits move separately

Some F2 plants were tall with wrinkled seeds. Others were short with round seeds. Neither combination was in the parents. This is possible because height and seed shape are inherited independently.

When plants differing in two traits are crossed, the F1 show both dominant traits, while the F2 include new combinations of traits. This shows that different traits are inherited independently.

Notes

Crossing plants that differ in two traits: F1 shows both dominant traits; F2 has new combinations, so different traits are inherited independently.

Check yourself

Both traits in the F1 plants of this cross were…

Which F2 plants show a new combination of traits?

What do the new combinations in F2 show?

Which traits are the dominant traits in this cross?

• tall and wrinkled seeds. The F1 plants all had round seeds. Wrinkled seeds were not seen in F1.
• short and round seeds. The F1 plants were all tall. Shortness was not seen in F1.
• tall and round seeds, the dominant traits — correct. Yes!
• Tall plants with wrinkled seeds — correct. Yes!
• Tall plants with round seeds. This combination was already in one of the parent plants, so it is not new.
• Short plants with wrinkled seeds. This combination was already in the other parent plant, so it is not new.
• Height and seed shape are inherited together as one unit. Tall plants with wrinkled seeds appeared, so the two traits do not have to stay together.
• Height and seed shape are inherited independently — correct. Yes!
• The F1 plants were a mixture of the two parents. The F1 plants were all tall with round seeds, with no mixture.
• Shortness and wrinkled seeds. These traits were not seen in the F1 plants, so they are not the dominant ones.
• Tallness and wrinkled seeds. Wrinkled seeds were not seen in the F1 plants, so wrinkled seeds are not dominant.
• Tallness and round seeds — correct. Yes!