How come drones are male bees, when they arise from unfertilized eggs?

Answer

Dear Susan,

Indeed, the sex of an organism can be determined in several ways, and this can be either genetic or environmental (as a combination) of both.

Within the gender-related sex determination you also have different options. Here you should know that you have two ‘types’ of chromosomes, the sex chromosome (just think of the X or Y chromosome in humans), and the autosomes (all other chromosomes). Both an egg cell and a sperm cell each have one set of chromosomes (i.e. a sex chromosome and the autosomes) and these are called haploid. When an egg cell is fertilized by a sperm cell, we get a diploid cell (a cell with two sets of chromosomes). Depending on which sex chromosomes you get from your parents (a mother can only pass on the X chromosome because she herself is XX – a father can pass on either the X or the Y chromosome, because fathers are of the XY type) you get daughters (XX) or sons (XY). This is the ‘standard’ sex determination as we know it in mammals.

Well, bees belong to the Hymenoptera group (along with wasps and ants). In these organisms, the sex is not determined by sex chromosomes, but by the number of sets of chromosomes that an individual receives. A queen bee egg that is fertilized results in a cell with two sets of chromosomes (also called a diploid cell) and these become the workers (or queens); an unfertilized egg can also develop although it has only one set of chromosomes (namely those of the queen) and these then become males or drones (having one set of chromosomes is also called haploid). Depending on the type of food that fertilized eggs receive from the workers, they will develop into workers or queens. So with bees it is simple: fertilized eggs become females (workers and queens), unfertilized eggs become males (drones). So what matters is how many SETS of chromosomes they have: one (haploid) or two (diploid); hence this type of sex determination is sometimes called haplodiploidy.

If you think about it further, you will also come to the following conclusions: drones have no father and no sons (only daughters because drones fertilize eggs and therefore only give rise to diploid cells), but they do have a grandfather and grandsons. ..

Greetings,

Kurt Jordans

Royal Museum for Central Africa – Entomology