An Explanation Of Haplo-Diploidy Reproduction

This page is credited in full to Dave Cushman who created it. His voice is expressed in black colour text and any additions or comments in blue belong to myself. Credit: Dave Cushman’s website.



An Explanation Of Haplo-Diploidy Reproduction

Much of this text is not mine, many of the words are attributed to David H. Headrick, I have merely presented some of his words in an editorial sense in order to help those that have difficulty understanding the difference between human and honey bee reproduction.

There are two types of cells somatic cells and germ cells. Somatic cells form the various tissues and organ systems of the body, bone, muscle, liver, heart, brain, etc. Germ cells form the reproductive tissue from which gametes (sperm and eggs) arise.

In humans, each cell (somatic and germ) has a full complement of chromosome pairs; this condition is known as diploid. However, when the germ cells divide to form gametes, each gamete receives only one set of chromosomes; this condition is called haploid or having one half the number of chromosomes. When an egg and sperm unite the diploid condition is restored.

The most common form of reproduction in insects is sexual. Males and females are present in populations and males pass their haploid gametes to females for fertilization of the haploid eggs to produce a diploid zygote; this form is also called biparental (ie… two parents).

Reproduction can take place in the absence of male gametes, but is not as common. This is termed Asexual reproduction or parthenogenesis (Latin for virgin birth). In this form, eggs produced by females are diploid (they carry the full complement of chromosomes) and develop into females that are genetic clones of their mothers. Many species of aphids, some weevils and some Hymenoptera have this form of reproduction.

A combination of sexual and asexual modes called haplo-diploidy occurs in four insect orders, the Coleoptera, Hymenoptera, Thysanoptera, and Hemiptera. Haplo-diploidy occurs in most of the Hymenoptera or about 100,000 known species. In this form male gametes are haploid and the eggs produced by females are also haploid. Mated females have the choice of fertilizing an egg or not. Unfertilized eggs become male, and thus remain haploid. Fertilized eggs become female, and are diploid.

Our honey bee is a particular example of this type of reproduction. Queen bees are fertilized by haploid drones. The queen then lays fertilized eggs which become female workers. Occasionally the female will lay unfertilized eggs that ultimately become drones.

This takes place in most insects in the median oviduct. Sperm that has been stored in the spermathaeca enters the oviduct by way of a thin tube, and as the egg passes by the sperm enter the egg through the egg shell or chorion through a small opening in one end, known as a micropyle. Fertilization is deemed to take place when the sperm and egg nucleus unite.
Sex Determination

The chromosomes of insects, like most animals occur in pairs. (There are sixteen pairs in honey bees.) There are two types of chromosomes, autosomes and sex chromosomes, there is usually a single pair of sex chromosomes and the genes associated with these chromosomes account for an individual’s ‘maleness’ or ‘femaleness.’ In humans, the sex chromosomes are structurally different. Females have two similar chromosomes called X chromosomes (designated as XX), whereas males have an X chromosome and a smaller Y chromosome (XY). The presence of the Y chromosome, rather than two X’s, is what accounts for being male. In insects, however, the males generally have just one sex chromosome instead of a pair, this condition is referred to as XO. Female insects are generally XX.

In human male gametes, each sperm has either an X or Y chromosome; in eggs the sex chromosome is always X. Thus, the gender of the offspring is determined by whether an X sperm joins with an egg making an XX female, or a Y sperm joins with an egg producing an XY male. In insects, the sperm which does not have a sex chromosome thus creates a male insect (XO).

Yes it is complicated. 🙂


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