The origin of IBD segments is depicted via a pedigree of 12 individuals. Each box (male) and circle (female) represents an individual with two homologous chromosomes as bars. The top row shows three couples with their chromosomes colored differently. Due to crossing over, offspring inherit recombinant chromosomes of their parents. The first order cousins in the bottom row share one IBD segment (borders marked by grey lines). Both have inherited this IBD segment from the same individual, namely their grandfather (orange colored chromosome in the top row).