Biological organisms are composed of phenotypes and genotypes. The phenotype is the physical characteristics such as the stem length or the presence of flowers, while the genotype refers to the genes that an organism possesses.
Genes or genotype determine what the phenotype of an organism will be and are the characteristics that are inherited from parents to offspring. Because genotype is what is inherited, we can determine the ancestry of an individual by studying its genes or genetic sequence and therefore, know if it has ancestors in common with another organism.