I don't know the lesson you are referring to, but I do know the patterns of inheritance...
1. Complete Dominance- In this pattern, the only way to have a recessive gene is to not have any dominant genes. At. All.
2. Incomplete Dominance/Codominance
This is the only pattern that can use two different alleles
This is what happens when the offspring are show neither the dominant or recessive genes in their phenotypes, resulting in a kind of mix.
3. 2 Trait Crosses/Dihybrids
You solve this pattern with a 4x4 Punnett Square, and this pattern is used when determining 2 traits with 2 variations.
4. Sex Linked traits
Sex Linked Traits are passed down thru the female x chromosome.
5. Multiple Alleles
This pattern occurs when there are more than 2 alleles/genes to pick from, such as blood type.
6. Polygenic Inheritance
This pattern results in a gradient, and occurs when 2 or more set of alleles affect the same trait. You do not need to make a cross. An example of such a pattern is the amount of melanin every person has.