Genic Balance, Heterozygosity and Inheritance of Size of Testes in Diploid Drone Honeybees

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Abstract
In order to rear diploid drones with larger testes, the inheritance of testis size was investigated. The genie balance hypothesis was tested in relation to the different additive effects of various X-alleles. Different levels of heterozygosity of multiple loci were also considered. Apis mellifera adansonii and A.m. ligustica were crossed to determine the X-allele composition of the offspring; this resulted also in different degrees of heterozygosity in the progeny. About 300 queens were instrumentally inseminated, and haploid and diploid drones originating from 23 queens were investigated; 1460 testes were measured. The size of the testes of haploid drones of various groups differed very little. The average volume of the testes of various groups of haploid drones was 2·7–6·5 times as large as that of diploids of the same groups. Diploid drones of African bees had larger testes (mean volume 4·14 mm3) than those of Italian bees (mean 1·82 mm3), and backcrosses to Italian queens resulted in medium-sized testes (mean 2·76 mm3). Homozygosity of X-alleles reduced the size of the testes of diploid drones, but this size did not follow the X-allele compositions of the individuals. Thus the different additive ability of various X-alleles was not detected here. An increase of the heterozygosity of loci other than the X-locus did not decrease the size of diploid testes. The inheritance of this size was in accordance with additive action of special polygenes. Thus, breeding diploid drones with larger testes should be carried out on the basis of polygenes.

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