Concept:The phenotype is the total set of observable traits of an organism.
Explanation:Phenotype covers all visible features of an organism, including height, eye colour, and blood type.
A phenotype is produced by the interaction between the genetic constitution (genotype) and environmental influences.
For clarity, the genotype is the internal gene combination, while the phenotype is the outward expression.
Heterozygous means having two different alleles for a gene, and homozygous means having two identical alleles.
Neither heterozygous nor homozygous refers to observable features, so they cannot be the answer.
Thus, the phrase "sum total of all observable features" is best defined as the phenotype.
Answer:A. phenotype