We now go beyond generalities and plunge in chromosomes, genes
and alleles. We know that queens and workers hatch from eggs con-
taining two sets of chromosomes, one set of 16 from each parent
(diploid), and that drones hatch from eggs containing one set of
chromosomes (haploid). This letter process of drones hatching from
unfertilised eggs is termed parthenogenesis.
The chromosomes contian hereditary units called genes. The specific place on a chromosome where genes are found is called a locus. On
rare occasions a gene entering an egg or sperm has changed or
mutated and will have a different effect than the original gene. All
the forms of a gene that occur at a locus are called alleles. Allele is
just a word that means version of a gene. For example, genes for blue eyes and brown eyes are alleles (or different versions) of the eye
colour gene. There is a gene that controls the sex of a bee and is
of course called the sex allele. If there are two different sex alleles
present, the bee will develop into a female (worker or queen). If
there is one allele present, the bee will develop into a drone. There
are two ways that only one sex allele could be present. Firstly as we
have seen, the egg may be unfertilised and so will only contain
one sex allele anyway; and secondly, both the mother and the father
may contribute the same allele in a fertilised egg and this egg even
though fertilised will also develop into a drone. The drone will then
have two sets of chromosomes instead of the normal one (i.e. a
diploid drone) and will not be able to function as a normsl drone.
These diploid drones are always destroyed by workers who eat them
on hatching from the egg in the cell. When therefore inbreeding
occurs and it is more likely that the mother and the father will have
the same allele, the queen will lay eggs in worker cells that are in
fact diploid drones. These will be eaten and so the brood pattern
will be full of holes alternating with normal larvae. So the closer the
relationship between mating partners, the fewer the viable brood.
A brother/sister mating will preduce only 50% viable brood.
Genetic viability is therefore paramount and idea behind queens
flying to a Drone Congregation Area (DCA) to breed with as many
drones as possible from as many different and widespread colonies
as possible now takes on greater validity. Scientists believe that
there are about 19 versions or alleles of the sex gene and the more
such alleles that are present in our bee population, the more solid
will be our brood pattern and so the more bees will be available to
collect honey.
While sex determination is therefore generally complicated, other
charateristics can be even more complex. Different combinations
of alleles at a locus can result in many different expressions of
charateristics and all these different events result in complex
genetic systems that produce a wide variety of charater expression in bees. Alleles at other loci can also affect a charateristic. For example, workers exposed to a component of the alarm pheromone,
isopental acetate was estimated to be influenced by at least 7-8
genes and this variety is some of the raw material necessary for the
genetic improvement of bee stocks.