I read this in wikipedia. It explains what happens when a queen mates with one of her brothers. It emphasized the need for more hives of genetic diversity when mating queens. The result is you can end up with spotty brood since after the egg hatches in 4 days the young brood is detected and removed leaving holes in the brood that the queen has to relay in. I Know it is rewarding to raise your own queens but if you don't have enough bee hives in your area to provide non related drones your queens are going to be inferior because of the amount of brood being removed because of diploid drone eggs. "Drones are produced from unfertilized eggs and therefore represent only the DNA of the queen that laid the eggs, i.e. have only a mother. Workers and queens result from fertilized eggs and therefore have both a mother and a father. A modified form of parthenogenesis controls sex differentiation. The sex allele is polymorphic and so long as two different variants are present, a female bee results. If both sex alleles are identical, diploid drones are produced. Honeybees detect and destroy diploid drones after the eggs hatch. Queens typically mate with multiple drones on more than one mating flight. Once mated, they lay eggs and fertilize them as needed from sperm stored in the spermatheca. Since the number of sex alleles is limited - about 18 are known in Apis - there is a high probability that a queen will mate with one or more drones having sex alleles identical with one of the sex alleles in the queen. It is therefore typical for a queen to produce a percentage of diploid drone eggs."