Answer:
In a pedigree chart, a filled-in symbol (usually a circle or square) typically indicates that the individual represented by that symbol has the trait or condition of interest. This trait or condition may be a genetic disorder or a physical characteristic that is being studied.
For example, in a pedigree for a genetic disorder such as Huntington's disease, a filled-in circle or square would indicate an affected individual who has inherited the disease-causing allele from one or both parents. In contrast, an unfilled symbol would indicate an individual who does not have the disease or does not carry the disease-causing allele.
Overall, the use of filled-in symbols in a pedigree chart helps to visually represent the inheritance pattern of a trait or condition within a family.