Question

What is dominance and recessiveness?

(I even want to know this in terms of presence of a gene that makes a protein.)

Answer 1

Sexually reproducing organisms carries 2 allele for gene. The two allele may be similar to each other or different. The difference in the allele is based on the protein they code for. If the the two alleles codes for different kinds of proteins then they will show different traits as well and finally a different phenotype. Presence of single dominant allele in a person can produce a dominant phenotype in the individual hiding the effect of recessive allele. While for a recessive phenotype to get expressed there is a need that recessive allele should be in a  homozygous (Both the alleles are recessive) condition in an individual. Presence of a dominant allele (expressing a dominant protein) with a recessive allele in an individual hides the effects of the recessive allele (protein expression by recessive gene).