Conventional cytogenetic techniques can distinguish homologous chromosomes in a qualitative manner based upon obvious morphological features or using in situ hybridization methods that yield qualitative data. We have developed a method for quantitative genotyping of single-nucleotide variants in situ using circularizable DNA probes, so-called padlock probes, targeting two different alpha satellite repeat variants present in human chromosome 7 centromeres, and a single-nucleotide variation in alpha satellite repeats on human chromosome 15 centromeres. By using these PCR-generated padlock probes, we could quantitatively distinguish homologous chromosomes and follow the transmission of the chromosomes by in situ analysis during three consecutive generations.