**7. Finding polymorphic frozen blocks and their ancestral haplotypes**

The best clue to the location of these blocks is segmental duplication [17, 37].

To characterize the PFB, it is helpful to amplify haplospecific geometric elements [30], see also Table 3. Essentially, this approach reveals duplications as seen in Figure 8. McLure developed the approach to find PFB throughout the genome [36]. Paralogous regions are also helpful as shown in Figure 9.

Once identified, we recommend tracking the polymorphism through panels of multigenera‐ tional families as illustrated in Figure 10. Although the region is over 10 megabases, recombi‐ nation was not found. The different haplotypes in the three breeds must have been conserved for at least hundreds of generations and mark differences in function such as the melting point of fat [37].
