Other contributors have said "Are dominate alleles that cause lethal disorders are more common in populations than recessive alleles tha cause disorders?" is the same question as "Why are most lethal genetic disorders recessive?" If you believe that these are not asking the same thing and should be answered differently, click here
If these genetic disorders were to be caused by homozygous alleles they would selected against and would be removed from the population. The recessive alleles can remain hidden in heterozygotes.
A carrier is a person who has one recessive allele for a trait, but does not have the trait. For example (where colorblindness is the trait [the trait is noted as c): Jamal and Kim is a couple. Jamal...