Haplodiploid sex-determination system

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The Haplodiploid sex-determination system is a system that some Hymenopterans (bees, ants, and wasps) use to determine the sex of their offspring, and preserve eusociality. In this system, there are no sex chromosomes. Instead, the sex is determined by the number of chromosomes. Haploid offspring (which are from unfertilized eggs) are males, while Diploid offspring (which are fertilized eggs) are females.

In honeybees the drones (males) are entirely derived from the queen, their mother. Males do not contribute to males - therefore males have no fathers or sons. The genetic makeup of the female worker bees is half derived from the mother, and half from the father. Thus, if a queen bee mates with one drone, her daughters share 3/4 of their genes with each other. The diploid queen's genome is recombined for her daughters, but the haploid father's genome is inherited by his daughters "as is". Although the queen lays eggs with a 1:1 sex ratio, the worker bees manipulate the feeding of offspring so that a sex ratio of 3:1 (females to males) is preserved. The worker bees are short lived and are constantly being replaced, so this kin selection is possibly a strategy to ensure the proper working of the hive.

Shared gene proportions in haplo-diploid sex-determination system relationships

Sex	Daughter	Son	Mother	Father	Full Sister	Full Brother	Niece/Nephew
Female	1/2	1/2	1/2	1/2	3/4	1/4	3/8
Male	1/2	0	1/2	0	1/2	1/2	1/4

Since a queen normally mates with 10-15 drones, and holds the semen fairly discretely separated, the workers make up subfamilies within the hive. When a queen runs out of semen from one drone, and begins to lay eggs fertilized by sperm from another, the behavioral characteristics of the hive (which are genetically determined) can change significantly. There is a heritable variation in the expression of different types of social behavior. When the daughters of particular drones are tracked, they tend to be in the same 'occupation' in the hive (workers, guards, etc.).

If a queen accidentally mates with her brother, there will be large gaps in brood production, either from nonviability of the eggs, or by removal of such eggs by workers.