Technology Student
Technology Student: Mechanisms
This site describes mechanisms and simple machines, and the basic components used to build them.
Khan Academy
Khan Academy: The Law of Independent Assortment
Article defines Mendel's law of independent assortment, provides examples, and takes a look at how it is used to make predictions. Also, discusses dihybrid crosses and 4 x 4 Punnett squares.
California State University
Linkage Animation
This animation takes the learner through the steps of linkage and tells how linkage is different from other processes. There is a small quiz available once the animation is finished.
Other
Hognosesam: Linkages
This site illustrates different types of linkages that are used to create different types of levers.
Other
D&t Online: Linkages
This site describes different types of linkages and how they are used in simple machines.