Figure 1. Representation of the coinheritance (i.e. genetic transmission) of a disease-causing mutation or genetic variant and surrounding ‘founder’ chromosomal material over a number of generations. Homologous chromosomes are depicted by solid vertical lines. The numbers represent repeat lengths (alleles) associated with a microsatellite locus. The letters designate bases (alleles) at three single-nucleotide polymorphic loci adjacent to the microsatellite locus. The circled ‘G’ base is a dominant and fully penetrant disease causing mutation. The arrows identify sites where recombination has occurred. In generation 1, two individuals produced 4 offspring and two that received the disease mutation (i.e. the inner two offspring). One of these offspring did not receive the entire chromosomal segment or ‘haplotype’ (123-C-G-T) associated with the parent introducing the mutation into the population due to a recombination event which shuffled the 126 allele at the microsatellite locus with the C-G-T subhaplotype. The individuals possessing the mutation produce their own offspring and these offspring produce subsequent lines of descent (denoted by the dashed lines). Two descendants of these individuals (in generation N–1) mate with others and produce two offspring each. The two offspring from both matings receive the disease mutation, G. Note, that all the diseased individuals share the basic core C–G–T haplotype, but in the first mating the repeat allele 126 is coinherited with this haplotype while the repeat allele 123 is coinherited with this haplotype in the second mating.