> I'm curious as to what causes a haploid drone from an inbred population to be weaker?  Is it a cytoplasmic or epigenetic effect?

First, I wish to state that my research indicates that these drones are not common for the reason that honey bees in general are not overly inbred, that they are not much of a problem since they would be unlikely to mate, but that there is an interesting flip side, which is to what degree does heterozygosity *improve* the quality of colonies. 

But back to inbreeding, one symptom is fluctuating asymmetry. This has been documented in humans, where the two sides of the face are not exactly the same. It appears that we are attracted to very perfect faces for a reason, these people have a more diverse genetic background. 

My chief interest in the whole question was whether there is a characteristic genetic signature of homozygosity (inbreeding) or heterozygosity (vigor). Apparently by crunching the genomic data, some folks have found inbreeding coefficients that may be useful in evaluatung for stock selection. More work to do.

Meanwhile here is a bit on FA:

> Fluctuating asymmetry is often assumed to be negatively correlated with developmental stability: since both the genotype and the gross external environment are usually considered to be the same for the left and right sides of a developing organism, all deviations from perfect bilateral symmetry in the fluctuating case should be the result of accidental perturbations of developmental pathways.   

> Many studies have noted a decrease in asymmetry with increasing heterozygosity.  Lerner (1954) suggested that heterozygosity increases developmental stability, and thus decreases fluctuating asymmetry. His prediction is supported by associations between fluctuating asymmetry and several correlates and measures of genomic heterozygosity, including inbreeding levels. 

> It is not clear from these studies if the important feature is heterozygosity at specific loci or overall level of heterozygosity throughout the individual’s genome. In addition, the developmental mechanisms whereby interactions within and among loci affect asymmetry are unclear (but see MacKenzie and Clarke, 1988).

Fluctuating asymmetry in the honey bee, Apis mellifera: effects of ploidy and hybridization
D. R. Smith, et al      J. evol. biol. 10 (1997) 551 574

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