Try out PMC Labs and tell us what you think. Learn More. Sex chromosomes have many unusual features relative to autosomes. Y or W chromosomes lack genetic recombination, are male- female- limited, and show an abundance of genetically inert heterochromatic DNA but contain few functional genes. X or Z chromosomes also show sex-biased transmission i. Their unusual ploidy level and pattern of inheritance imply that sex chromosomes play a unique role in many biological processes and phenomena, including sex determination, epigenetic chromosome-wide regulation of gene expression, the distribution of genes in the genome, genomic conflict, local adaptation, and speciation. The vast diversity of sex chromosome systems in insects—ranging from the classical male heterogametic XY system in Drosophila to ZW systems in Lepidoptera or mobile genes determining sex as found in house flies—implies that insects can serve as unique model systems to study various functional and evolutionary aspects of these different processes. In many eukaryotic organisms, the two sexes have different chromosomal constitutions. Typically, one sex called heterogametic has a pair of morphologically different chromosomes, and the other sex called homogametic has two identical members of each chromosomal pair. In species with male heterogamety, the sex chromosomes are referred to as X and Y chromosomes XX females and XY males , whereas they are termed Z and W chromosomes in species with female heterogamety ZZ males and ZW females.
Energy, Ecology and Sex
Publication types
Address correspondence to Doris Bachtrog at the address above, or e-mail: dbachtrog berkeley. Insects harbor a tremendous diversity of sex determining mechanisms both within and between groups. For example, in some orders such as Hymenoptera, all members are haplodiploid, whereas Diptera contain species with homomorphic as well as male and female heterogametic sex chromosome systems or paternal genome elimination. We have established a large database on karyotypes and sex chromosomes in insects, containing information on over species covering 29 orders of insects. This database constitutes a unique starting point to report phylogenetic patterns on the distribution of sex determination mechanisms, sex chromosomes, and karyotypes among insects and allows us to test general theories on the evolutionary dynamics of karyotypes, sex chromosomes, and sex determination systems in a comparative framework.
The science behind it all
Female barklice of the genus Neotrogla have this pronounced genital structure, called a gynosome, which some researchers argue constitutes a female penis. Genitals are among the fastest-evolving features in the animal kingdom. Ducks have corkscrew-shaped genitalia. Female cabbage white butterflies have a hinged jaw inside their genital tract. Nature is full of strange reproductive organs with unusual uses. For the most part, though, certain genital morphologies are associated with males, others with females. But in , a tiny insect called the barklouse broke even that rule when researchers reported that the females of all four species of a genus found in the caves of Brazil had a penis.
A species of stick insects found in Britain have stopped having sex with their male counterparts and become a female-only population. The insects - found off the coast of Cornwall - reproduce asexually without the need of male sperm. Clitarchus hookeri - originally from New Zealand - came here by "accident" when plants were brought across. And it took just generations for the species to evolve "barriers to sexual reproduction". Biologists in New Zealand took the insects back to find out what happened more closely. This particular stick insect species is found on the Scilly Isles and is "capable of both reproducing sexually - which is the way most multi-cellular organisms reproduce - and also asexually". Asexual just means only an egg is needed for fertilisation instead of requiring sperm. It's common in other insect species but she says it can be "short-lived" and lead to "an evolutionary dead end".
