Honey Bees: From Genotype to Phenotype

DNA, deoxyribonucleic acid, is the blueprint for the making of an individual organism. A gene contains a sequence of nucleotides, which then is converted into a sequence of amino acids that produce a protein. Proteins are used to build cells and determine how those cells function. For example, some proteins are enzymes that produce chemicals that are used as pigments for hair. The sequence of a gene can vary, and these different gene variants are called alleles. If the sequence of the gene varies, the amino acid sequence of the protein can vary, and these different proteins may have different activities. These different activities can result in different structures or processes. For example, if a protein that produces a pigment is not functional, then the pigment is not produced, and the individual has a different hair color. 

An individual's genotype, or genetic makeup, describes all the genes that are present in the DNA (or genome) of an individual. The traits that result from the activity of the proteins of those genes are called the phenotype. Honey bee phenotype examples are exoskeleton color, pollen hoarding behavior, and resistance to chalkbrood.

Some traits are inherited from a single gene, while others are the result of multiple genes. Thus, it is important to understand how inheritance plays a role in the honey bee traits that are targeted by breeders.

The Cordovan coloration of bees is a recessive trait carried on a single gene. That is, if a female bee receives two copies of the recessive gene, she will have a brown exoskeleton rather than the normal black exoskeleton. Because drones are haploid and only inherit one set of genes, they will have a brown exoskeleton with just one copy of the recessive gene.

Most traits are much more complicated in their inheritance. For example, there are at least two but up to nine genes involved in the inheritance of hygienic behavior in bees (Boutin et al. 2015).

In addition, the environment plays a role in the expression of many genes. This is called epigenetics. For example, workers and queens both begin as fertilized eggs. The quality and quantity of the diet fed to the larva influences the expression of genes associated with the queen or worker phenotype. Another example of epigenetics is the winter bee phenotype. Honey bees receive signals from the environment in the fall, such as lower temperatures, fewer hours of daylight each day, and reduced food intake by the colony, and develop into longer-lived winter bees to survive winter in a cluster.  However, researchers still have not identified the environmental factors that trigger the production of winter bees.

Epigenetics influences the expression of many traits of honey bees, which can make breeding a challenge. Researchers have observed both increased and decreased expression of mite resistance behaviors during strong nectar flows and during dearths. This is both fascinating and a source of frustration for beekeepers and researchers.

The fact that honey bee phenotypes vary throughout the season is an important consideration for honey bee colony evaluation and breeding efforts. By carefully comparing colony performance at similar time points and choosing breeding stock from colonies that express desirable traits over the course of more than one season, beekeepers can select stock with stable trait expression.

References:

Boutin S, Alburaki M, Mercier PL, Giovenazzo P, Derome N. Differential gene expression between hygienic and non-hygienic honeybee (Apis mellifera L.) hives. BMC Genomics. 2015 Jul 7;16(1):500. doi: 10.1186/s12864-015-1714-y. PMID: 26149072; PMCID: PMC4491870.

This material is based upon work supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, through the Northeast Sustainable Agriculture Research and Education program under subaward number LNE22-447.