How is it possible for an offspring to exhibit a recessive trait if neither parent exhibited that recessive trait? What must be true about the parents’ genes for this to occur?

it is possible for an offspring to exhibit a recessive trait if neither parent exhibited that recessive trait if both parents are heterozygous for the trait. The parents' genotype must be heterozygous i.e., having one dominant allele and one recessive allele.

Explanation: It is possible for an offspring to exhibit a recessive trait when neither of the parents exhibited the recessive trait.

For example, if (A) is the allele for normal skin colour and it is dominant to (a) which is the allele for albinism that is recessive, two parents with heterozygous genotype Aa will have offsprings with the following possible genotypes: Aa x Aa = AA, Aa, Aa and aa.

One of the offsprings will inherit recessive allele for albinism from each parent (aa), and thus will manifest outwardly as albino child.

allowed for the prediction of the properties of missing elements.