Genetics 6
Genetics of the Drone

The queen possesses two sets of 16 chromosomes each associated with a sex allele (a1 and a2). Thus the egg laid by the queen contains a set of 16 chromosomes which is associated with either allele a1 or a2. This unfertilized egg which produces a drone is haploid. Because of crossover and the random arrangement of the chromosomes at the metaphase during meiosis each drone is of a unique genotype, i.e. the drones only contain their mothers genes but nevertheless each is genetically unique. This has been simplified on the diagram.

Since each drone has only one set of 16 chromosomes its sperm can only contain that single set of 16 chromosomes. All sperm from a single drone are clones.

So whereas the egg which the queen lays has a great deal of generic diversity because of crossing over, the sperm from the drone has none.
Genetic diversity

The multiple mating of the queen in which 10 drones or more might be involved ensures that only a small number of them will share the same sex alleles as the queen. By instinct the queen collects a mix of sperm which ensures that there is a maximum amount of genetic diversity in the hive.

Each worker belongs to a sub-set of sisters having the same father and sharing 75% of their genes, i.e. they share 50% of the queen's genes but 100% of the drone's.

However, the different sub-sets of workers share the same mother but have different fathers and hence only share 25% of their genes. This genetic difference in relationship has many effects on the life and work of the colony.

The genetic shuffle which starts with crossing over of genes before meiosis and continues with the random shuffle of chromosomes at the metaphase stages, ensures that the egg so formed already contains a genetic mix before fertilization; making each bee in the colony genetically unique.
drone genetics
genetics of the queen and workers
Genetics of the Queen and Workers

The diagram below illustrates the situation when the queen mates with a number of drones. (5 drones are shown for simplicity on the diagram but 10 is the norm).

The drones are haploid each assumed to have a different set of 16 chromosomes each with a different sex allele.
The queen is diploid with 2 sets of 16 chromosomes with 2 sex alleles. The queen lays an egg with one set each of 16 chromosomes and 1 allele, but now this egg is fertilized by sperm from the drone.
The result is a worker having 2 sets of 16 chromosomes and a combination of 2 alleles. (A queen may result instead of a worker but she will have the same 2 sets of 16 chromosomes and 2 associated alleles.) The queen and workers are thus diploid.
Next page: Genetics 7.
gemetic diversity
In August 2013 one of the colonies started producing bees with an orange banding on the first and second tergite. The colony had a new queen and the normal colour of the worker would be expected to be very dark brown or black. These orange bees came as a complete surprise.

These bees look very like a Buckfast bee. But in so far as I have never had Buckfast bees (nor are there any in the neighbourhood as far as I know) it is difficult to explain where these came from. The new queen is the grand daughter of the queen I have used for breeding so I would assume that she is from the line of black bees. But clearly either the new queen must have mated with a Buckfast drone or had been carrying Buckfast genes which had up till now have remained hidden.

This observation illustrates the genetic diversity which is present in all colonies but is not otherwise so apparent.

It will be interesting to observe this colony and follow what happens to these orange bees.
copyright©2017 killowen.com
Terms of Use