How do dominant and recessive alleles affect phenotype?
Your phenotype depends on the dominant allele.
If you have one dominant allele and one recessive allele, your phenotype will appear from the dominant allele.
For example, if you have a brown eye colour allele, and the blue eye colour allele, then you would result in having brown eyes from your phenotype, as the brown eye allele is dominant.
Dominant alleles are denoted by capital letters, such as "B", while recessive alleles are denoted by lowercase letters, such as "b".