Understand an allelic series -How many possible alleles are there for any given gene? Is there only one recessive allele for a gene? Is there only one dominant allele for a gene? Is an allele always recessive or dominant with respect to other alleles of the gene?
What is a lethal allele? Are lethal alleles usually dominant or recessive? Are there any exceptions? (Hint: Huntington disease in humans). How do we maintain stocks with lethal alleles?
How can you tell if an allele is lethal? If one of the parents has a lethal allele, would all the possible genotypes be present in the progeny? What would happen to the phenotypic ratios of the progeny?
What is pleiotropy?
How can you tell if a trait is determined by more than one gene? What ratios of phenotypes in the F2 generation would you expect if a trait is determined by a single gene?
What is epistasis? How can the genotype at a locus affect the phenotype determined by the genotype at another locus? What are complementary gene action, duplicate gene action, dominant suppression, dominant epistasis, and recessive epistasis?