Haplodiploidy means that a male develops from an unfertilized egg and is therefore haploid. Females develop from normally fertilized eggs and are diploid.

Sisters are related by .75

Haplodiploidy occurs in the Hymenoptera: the ants, wasps, and bees. Termites, as well as ants and the more highly organized wasps and bees are eusocial. Eusocial insects: 1) cooperate in caring for the young; 2) have a reproductive division of labor with sterile individuals helping to raise the offspring of their producing nestmates; and, 3) the overlap of generations means that offspring assist parents at some time in their lives.

An obvious advantage of haplodiploidy in these insects is that it seems to minimize the "cost of sex." That is, haploid males are produced only when the queen cannot lay any more fertilized eggs that will develop into diploid females.

A cautionary note: The relatedness values we have just calculated assume that the queen only mates with 1 male. If two workers do not share the same father, they are only related by .25. In honeybees whose queen mates up to 20 times, the average relatedness is far less than .5. However, workers are able to discriminate between suisters that are more or less related.

Modified from a page on Altruism in Social Insects.
Note: Haplodiploidy occurs in insects other than the hymenoptera.

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