You should know that both red/green color vision and hemophilia are sex linked traits.  Study Objectives 19 and 20 for the procedure you use when you work a problem involving a sex linked trait. In particular, note that males have only ONE gene for a sex liked trait. Note how the genotype for males involving sex linked traits is written.
Recessive alleles are always written using a lower case letter.
A genotype that is heterozygous is one in which the two alleles are not the same.
A monohybrid cross is one that is concerned with the inheritance pattern of ONE trait.  A dihybrid cross involves two traits (for example,LLGg X Llgg).  In reality, crosses involve thousands of traits!  One would need a computer to even begin to follow such crosses!
Many characteristic are controlled by more than two allelic forms.  The ABO blood group is the traditional example of multiple alleles used in beginning biology.  One's blood type is determined by any combination of two of the following alleles - I^A , I^B, and i. For example, an individual of blood type A (the individual's phenotype) could have the genotype of either I^AI^A   or I^Ai. This is also a good example of dominance relationships. Note that alleles I^A and I^B are codominant whereas i is recessive to both I^A and I^B.
A WORD is used to describe a phenotype (not letters). When letters are used one is specifying either an allele or the allele that a gamete contains.(example L ) or a genotype (example AA).