ARS | Publication request: THE NUMBER OF GENES INVOLVED IN THE SMR TRAIT

Submitted to: American Bee Journal
Publication Type: Abstract
Publication Acceptance Date: April 15, 2005
Publication Date: May 1, 2005
Citation: Harbo, J.R., Harris, J.W. 2005. The Number of Genes Involved in the SMR Trait. American Bee Journal 145(5):430

Interpretive Summary: Suppressed mite reproduction (SMR) is a trait of the honey bee that provides resistance to a parasitic mite, Varroa destructor. This report estimates the number of genes that contribute to this trait by evaluating 28 gametes (drones) produced by a queen that was heterozygous for the trait. For example, if one gene is involved in the SMR trait, about half of the drones (14) from a heterozygous queen would have the SMR allele and 14 would not. If there were two genes involved, about 7 drones would have zero, 14 would have one, and 7 would have two alleles. As the number of genes increases, we expect fewer drones with zero or all-possible alleles (frequencies of zero and all should be equal). For the field test, we mated 28 drones (single drone inseminations) to queens that had 100% of the alleles for the SMR trait. We established 28 colonies with these queens and measured mite reproduction after the queens had been laying for 8 weeks. We calculated the percentage of nonreproducing mites in each colony by evaluating 30 mite-infested worker cells 8-10 days postcapping. Results suggest that there may be two genes involved in the SMR trait and that the alleles may be additive. However, two is only a working hypothesis and estimate. The strongest case for 2 genes is the 1:2:1 distribution. About 25% of the colonies had 100% expression of the trait, about 25% were in a low grouping, and the rest were grouped in the middle.

Technical Abstract: 8. Harbo, J.R.(h) & Harris, J.W.(h)¿ THE NUMBER OF GENES INVOLVED IN THE SMR TRAIT ¿ The SMR (suppressed mite reproduction) trait is explained by the hygienic removal of reproductive mites (Varroa destructor), see abstracts #9 and #10). This report describes what a breeder may expect when out-crossing or backcrossing bees with the SMR trait. To estimate the number of genes, we evaluated 28 gametes (drones) produced by a queen that was heterozygous for the trait. For example, if one gene is involved in the SMR trait, about half of the drones (14) from a heterozygous queen would have the SMR allele and 14 would not. If there were two genes involved, about 7 drones would have no SMR alleles, 14 would have one, and 7 would have two. As the number of genes increases, we expect fewer drones with none or all-possible alleles (the number of drones with none or all should be equal). For the field test, we mated 28 drones (single drone inseminations) to queens that (in our judgment) had 100% of the alleles for the SMR trait. We established 28 colonies with these queens and measured mite reproduction after the queens had been laying for 8 weeks. We calculated the percentage of non-reproducing mites in each colony by evaluating 30 mite-infested worker cells 8-10 days post-capping. Results suggest that there may be two genes involved in the SMR trait (see figure) and that the alleles may be additive. However, two is only a working hypothesis and estimate. The strongest case for 2 genes is the 1:2:1 distribution. About 25% of the colonies had 100% expression of the trait, about 25% were in a low grouping, and the rest were grouped in the middle. Figure Caption Frequency of reproductive mites in 28 test colonies (white bars). Gray bars represent an expected distribution of 28 colonies if there are: 2 genes involved, no colony variation, and no measurement error. Except for ¼ of the expected data being at 100% non-reproduction, the other expected frequencies have no predicted percentages and were subjectively placed to provide the best fit.