PBS
Pbs Learning Media: Mendel's Laws of Genetic Inheritance
This interactive activity, adapted from the Dolan DNA Learning Center, uses Punnett squares to illustrate Mendel's laws of inheritance and how a particular gene combination results in a 3-to-1 ratio of dominant-to-recessive traits.
Cold Spring Harbor Laboratory
Dna From the Beginning: Genetic Inheritance Follows Certain Rules
Find out what happened when Mendel crossed two hybrid pea plants. The animations do a good job explaining why these crosses produce a 3:1 ratio of traits.