How is a recessive allele different from a dominant allele apex?

For the trait that is coded by a recessive allele to be expressed, the must be homology, which means that an offspring has to inherit that recessive allele from both its parents.

A dominant allele will dominate over the recessive allele, so for the trait coded by a dominant allele to be expressed, the offspring only needs to inherit the allele from one of its parents.

For example: "R" is brown eyes, "r" is blue eyes.

Now you get one R from each of your parents.

RR (homozygote) = brown eyes

Rr (heterozygote) = brown eyes

rr (homozygote) = blue eyes