Agriculture Reference
In-Depth Information
Controlling for sex
The next complication stems from the first: the sex of bees is controlled by what
could be called a lethal gene, or sex allele. Despite a colony's fairly complicated family
structure and despite the fact that a male bee emerges from an unfertilized egg, the basic
principles of genetics still apply to bees. We must now, therefore, go beyond generalities
and plunge into chromosomes, genes and alleles.
The specific place on a chromosome where particular genes are found is called a locus.
All the forms of a gene that occur at a locus are called alleles. 'Allele' is simply a word
that means a version of a gene. For example, genes for blue eyes and brown eyes are
alleles of the eye-colour gene. Importantly in bees, there is a gene that controls a bee's
sex, and this, of course, is called the sex allele. If two different sex alleles are present, the
bee will develop into a female (worker or queen). If only one allele is present, the bee
will develop into a drone.
There are two ways that only one sex allele can be present. First, as described above, the
egg may be unfertilized and thus contain one sex allele only. Second, both the mother
and father may contribute the same allele in a fertilized egg, and so this egg - even
though fertilized - will also develop into a drone. The drone will therefore have two
sets of chromosomes instead of the normal one set (i.e. a diploid drone) and will not be
able to function as a normal drone. These diploid drones are always destroyed by the
workers, who eat them on hatching. When inbreeding occurs - i.e. when the mother
and father have the same allele - the queen lays her diploid drone eggs in worker
cells, and these eggs are subsequently eaten. The brood pattern will therefore be holes
alternating with normal larvae. Most beekeepers will have seen this shot brood pattern.
The closer the relationship between the mating partners, therefore, the fewer the viable
brood. A brother and sister who mate, for example, will produce only 50% viable brood,
and the brood pattern will look terrible.
Genetic variability is, therefore, of paramount importance and queens flying to a
drone congregation area (DCA) to breed with as many drones as possible from as
many different colonies as possible now assumes greater validity. Scientists believe
there are around 19 alleles of the sex gene and, the more such alleles present in the
bee population, the more solid will be our brood patterns and so the more bees will be
available to collect honey.
Search WWH ::




Custom Search