The author of your text describes the gene for sickle cell anemia as being recessive. I prefer to think of it as codominant. What is there about this gene and the way it is expressed that it would best be described as codominant?
What is incomplete dominance?
Describe what is meant by “continuous variation”.

Why do recessive X-linked traits occur more often in males than in females?
Explain the difference between Mendel’s first law and Mendel’s second law.

Why does nondisjunction occurred more frequently in older females? And don’t just say that it is because their eggs have been around longer.