Gregory, It’s arbitrary. This is just an example – you are free to sketch your own example, the point is that at the grandparent level, for this chromosome, there will be about two crossover points – you can place them anywhere you want – they are random. Then if you have two crossovers, you have three segments – which will alternate between the two grandparents. To sketch an example you are free to use 7-6-7 or 6-7-6 on this maternal chromosome. On the paternal chromosome, with two crossovers, you could show 4-5-4 or 5-4-5. Just remember in the preceding generation – for Great grandparents – to use the correct Ahnentafel numbers. In other word if a 7 segment is divided in the next generation, it will have to be 14-15 or 15-14 – your choice for an example. In actual chromosome mapping there is only one correct solution. And it will not be the same as the hypothetical example I show – it will be different and unique for each person. Jim