In social bees, sex determination is controlled by a haplodiploid system:

• Unfertilised eggs develop into haploid male drones ($n$).
• Fertilised eggs develop into diploid female workers or queens ($2n$).
• Male drones produce haploid sperm cells ($n$) by mitosis.
• Female queens produce haploid egg cells ($n$) by meiosis.

In a particular species of social bee, the haploid genome consists of 18 chromosomes in each gamete.