Given an individual who is heterozygous for a recessive disease (i. e., the wildtype allele is dominant), explain how a deletion could result in the expression of the recessive phenotype. Be sure to use the formal vocabulary for full points (3 points)

Let us consider that A signifies the dominant allele and letter a signifies the recessive allele. The dominant allele, A would demonstrate normal phenotype, on the other hand, the recessive allele, a would be accountable for the disease. The possibilities of genotypes and phenotypes would be AA demonstrating normal homozygous individual, Aa demonstrating normal heterozygous individual, and aa demonstrating homozygous individual carrying the disease.  

Based on the given question, the genotype of the individual would be Aa, due to the existence of the dominant allele, normal phenotype would be demonstrated by the individual. In case if the deletion of A allele takes place from the genotype, the left a allele would possess the tendency to show its effect and the expression of the recessive phenotype will take place.  

Hemizygous refers to the condition in which only one allele is found in a diploid organism, and the organism within which it takes place is known as hemizygote.