Pedigree problems are typical tasks in school genetics classes. However, they are perceived as difficult and often are not successfully completed. Therefore, the purpose of this study is to determine relevant factors that might have an impact on success in pedigree analysis. Based on previous research, we investigate the influence of the superficial appearance of the pedigree (relating to a well-known misconception), the mode of inheritance, content knowledge, reasoning abilities, the last biology grade, and mental effort. This means, we are simultaneously examining student and task characteristics. For this purpose, we analyse data from N = 135 students, who solved four pedigree problems each, using Generalised Linear Mixed Models (GLMMs). Specifically, we use multilevel logistic regression to determine the influence of the variables in question. The final model shows mixed results: For example, the represented mode of inheritance has no significant influence. The superficial appearance of the pedigree, in contrast, is one of the important predictors of success in identifying the present mode of inheritance. Therefore, our results imply that students make decisions based on misconceptions when analysing pedigree problems. This and all other results are discussed in order to infer implications for teaching and learning pedigree analysis.