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Honey Bee Genetics

Clones with No Sons and Males with No Father

Let's get straight to the point - bee genetics are downright weird!

Most of us have heard of the importance of genes, how a mother and father each contribute their important element and so on. We accept, without question, that the mother contributes chromosomes from her egg and the father from his sperm. Much of the animal kingdom operates with these principles.

But that is not the case with honey bees.

But that is not the case with honey bees. They use an altogether different approach to the passing of chromosomes, with some strange implications. For example, consider these facts about drones, the male bee.

  • They have no father
  • They have a grandfather
  • They can be fathers to daughters, granddaughters and grandsons
  • They can't have sons

Confused? Read on...

Diploid and Haploid

The cause of all this weirdness is a sex-determination system called haplodiploidy. In high school biology we were taught that all eggs are fertilized and either female or male offspring result. Such is the case with humans, for example.

But in the curious world of the honey bee, a male is created from an unfertilized egg - just an egg laid by a queen, without being fertilized by sperm. The male bee is referred to as hapliod. The process of reproduction from unfertilized eggs is called parthenogenesis.

The more familiar situation, where the queen fertilizes an egg with sperm, results in a female bee. This means the egg is destined to be either a worker a queen bee. Female honey bees are referred to as diploid.

Haploid or Diploid
Male bees are referred to as haploid and females are diploid.

If you'd like to drill down a little more on this topic, check out this video from Jon Zawislak, at the University of Arkansas, Division of Agriculture.

The Impact on Genes

So what does all this mean in terms of the transfer of genes across generations? Let's consider, as a baseline, how humans compare.

Our genes are contained in chromosomes. We receive 46 chromosomes - 23 from our mother and 23 from our father. The transfer of genes through the generations means the characteristics of both sides of our family are evident in us and represented by factors such as eye color, height and so on. This is all because we result from an egg contributed by our mother and sperm contributed by our father.

With bees, the same basic principle exists - but only in female bees.

Female bees are created when a queen lays an egg that she then fertilizes. Though the numbers are different with bees (as compared to humans), each side of the family contributes the same number of chromosomes (16).

But it becomes a little stranger when we turn to the haploid - the drone. Male bees only include the chromosomes from the egg, since they have not been fertilized. Thus, drones have just 16 chromosomes, all from the queen.

Chromosome Counts
16 chromosomes from the queen + 16 from the sperm of the drone = female (worker or queen). 16 from the queen + 0 from the sperm of the drone = male (drone).

Mixing vs. Cloning

A queen's eggs contain 16 chromosomes. Thus, since she herself has 32 chromosomes (remember, as a female she has chromosomes from both her mother and father), she cannot "squeeze" all her 32 chromosomes into each egg. This means that eggs from a queen have a variety of combinations of chromosomes, from the queen and the sperm-donating drone.

Compare this with the drone. He has 16 chromosomes and his sperm can contain just that same number. And so, each sperm created by the drone is identical, since they all have the same 16 chromosomes. This makes for the creation of clones! Drones produce clones.

The Benefits of Genetic Diversity

With this fascinating background, let us turn to the issue of genetic diversity. One cannot underestimate the importance of diversity for bees. Where there is limited genetic diversity, the entire population is potentially vulnerable to the same diseases. If one of those hits the population then it can have a devastating effect.

By comparison, in a population with significant genetic diversity, a single disease may impact a percentage of the population, but others may be resistant. This means that genetic diversity reduces the chances of a catastrophic event wiping out the entire colony.

The Queen's Promiscuity

The queen's behavior at mating time has evolved to encourage such diversity. During her mating flights, early in life, she will mate with many drones. Since these drones have various genetic traits, they offer a genetic diversity that will serve the queen and her offspring well.

Her mating flights, across a few days, will result in collecting sperm from 10-25 dronesShe will store this sperm in her spermatheca for many years.

Back at home - perhaps in your beehive - she will start her life of laying eggs, around 2,000 per day. As she does so, she may or may not fertilize each egg, therefore deciding the gender. When she does fertilize an egg, she draws from a broad "stock" of sperm in her spermatheca. This means that all members of the colony have the same mother - the queen - but her female offspring have various fathers.

Her drone offspring will only have a mother, whereas if she fertilizes an egg to create a female she will use a sperm from one of many different potential fathers.

The Role of Royal Jelly

In looking at bee reproduction, the creation of queens vs. workers is interesting. Both, of course, are females and so have chromosomes from the mother (the egg-laying queen) and a father (through the sperm of a drone).

But what turns a fertilized egg result into a queen, as opposed to a worker? The answer lay in the feeding of royal jelly, a food fed to all larvae in their first three days.

In the majority of cases the feeding of royal jelly will cease after three days. This will result in either a worker or a drone, depending on whether the egg was fertilized. However, the colony will decide when it needs a new queen. When it does, a female larva will continue to be fed royal jelly, beyond the third day.

This changes the way in which genes are "marked" i.e. how they develop. Rather than promote the development of queen-relevant genes (as is often assumed), this  takes place through the limitation of worker genes.

How do bees make a queen?
They keep feeding her royal jelly, beyond her third day as a larva! The continued feeding of royal jelly inhibits the development of genes that would be found in a worker bee. It is the lack of these genes in a female larva that results in a queen.

How Beekeepers Can Hurt the Bee Population

As beekeepers we like to think we're helping the bee population and, therefore, the planet. However, an increasing number of beekeepers does not in itself mean the situation is improved. Without awareness, it may in fact be harmful.

Here's why:

As we have seen, genetic diversity is important for any species. And yet it's not uncommon for beekeepers - commercial or otherwise - to raise many queens from a single genetic line. This greatly constrains genetic diversity and, over time, leaves the population vulnerable to the wrong disease at the wrong time, with the potential to devastate the population.

For a deeper look at this topic here's a lecture by Debbie Delaney at the National Honey Show.

5 comments on “Honey Bee Genetics”

  1. Question. I'm into my second year of bee keeping here in So. Cal. I have an issue with highly aggressive bees. All my bees are from feral sources ie: cutouts, trap-outs and the majority from swarms. If these traits originated from Africanized gene lines, what is the greater source of these traits? Queen or Drones? Does requeening have as much an impact if the drones are still in the equation or is it a longer term effort of re-queening to gentle the colonies? Your opinions would be appreciated.

    1. This is really not an answer to your question but I also keep wild bees in southern California. The wild bees exhibit a range of behavior, from docile to aggressive. If I get a hive that is aggressive, I kill it. I don't want to deal with them and I don't want their genes going out into the wild gene pool.
      My definition of aggressive is that the bees follow you when you leave the bee yard and won't leave you alone. Docile bees leave you fairly quickly when you leave the bee yard. Don't put up with aggressive bees. There are a lot of swarms and cutouts available in our area to replace an aggressive hive.

  2. A queen has 32 chromosomes, 16 from her mother (queen) and 16 from her father (drone).
    When the queen "splits" her 32 chromosomes into 16 to lay a drone egg, which 16 chromosomes is she passing to the drone? Is she passing her mother's? Or her father's? Or some combination?

  3. The feeding of royal jelly does not trigger the change of cast from worker to queen. Bee worker larvae fed royal jelly in a laboratory only become poorly fed workers. It is thought that other substances fed to the queen larvae by hundreds of bees turn off the development of a worker allowing a queen to develop.

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