How many alleles must be present in order for a trait to show up in the offspring?

The characteristics or features that an organism has, such as eye color, skin color, hair color, tall or short is called a trait. In order for a trait to show up in the offspring, there should be two alleles present. One coming from the father, and the other from the mother. When fertilization occurs, the new offspring will have two alleles for every trait. The combination one has (coming from the father and from the mother) is called genotype. The two matching alleles is called homozygous while the two different alleles is called heterozygous. The allele that is expressed in heterozygous individuals is the dominant allele, while the allele that is not expressed is the recessive allele. The traits that are expressed make up you phenotype.

I’m confused so sorry