Final answer:
An unaffected individual can have alleles of a dominant trait in a pedigree, but they will not express the disease or condition associated with that trait if they are carrying a normal, healthy dominant allele. The statement that an unaffected individual cannot have any alleles of a dominant trait is false.
Step-by-step explanation:
In the context of a pedigree, an unaffected individual can indeed have alleles of a dominant trait. The assertion that an unaffected individual cannot have alleles of a dominant trait is false.
An allele is a variant form of a gene, and dominant alleles are those that express their traits in individuals even if only one dominant allele is present, which is the case in a heterozygous genotype (Aa). However, a person with a dominant disease or condition who does not show symptoms (unaffected) must not have the disease-causing dominant allele. Instead, they can carry a normal, healthy dominant allele. For a trait controlled by simple dominance, affected individuals have at least one dominant allele (could be AA or Aa). Significant information from a pedigree can come from analyzing the genotype of offspring; for example, two parents that appear unaffected but have an affected child must both be carriers of the recessive allele (heterozygous).
To understand completely, one must know that with autosomal dominant inheritance, an individual will show the dominant phenotype if they have at least one dominant allele, whether their genotype is homozygous dominant (AA) or heterozygous (Aa). Thus, a person with an unaffected phenotype could still have one or two copies of a dominant allele that does not cause any disease or condition.