Pre-eclampsia: a parent-offspring conflict

Genomic imprinting - the story of the other half and the conflicts of silencing

Genomic imprinting is an epigenetic mechanism that produces functional differences between the paternal and maternal genomes and plays an essential role in mammalian development and growth. There are a number of genes in our genomes that are subject to genomic imprinting where one parent's copy of the gene is expressed while the other is silent. Silencing of one allele predetermines that any function ascribed to that gene are now dependant on the single active copy. Possession of only a single active allele can lead to deleterious health consequences in humans. If imprinted genes are crucial in mammalian development, one would also expect mutations in these genes to cause diseases. Since imprinting is an epigenetic mechanism, mistakes in maintaining epigenetic mark also cause imprinting disorders. Here we in this review focus on the current understanding of this unique genetic mechanism more than two decades after the first description of the imprinting phenomenon was given by McGrath and Solter. Although the possible molecular mechanisms by which imprinting is imposed and maintained are being identified, we have a long way to go in understanding the molecular mechanisms that regulate the expression of these oddly behaving genes, the function of imprinting and the evolution. Post genomic technologies might ultimately lead to a better understanding of the 'imprinting effects'.

Death in Venice: the homosexuality enigma

A hypothesis is presented which regards homosexuality neither as an aberration of 'normal' human sexuality, i.e. heterosexuality, nor as a 'defect', genetically transmitted from parent(s) to offspring. Nor is homosexuality regarded as the regrettable result of accidental circumstances. Homosexuality, it is maintained, is simply inherent in the human reproductive strategy; an option which evolved during the millions of years of human evolution as a solution for problems inherent in a polygynic, yet social species living in relatively small groups: homosexuality diminishes intra-male competition on the 'reproductive market'. This enables males to work closely together in all fields of society (hunting, war etc), rather than competing with each other for access to females. Homosexuality thus largely contributes to group stability. However, because our present-day situation differs vastly from the situation in which the human reproductive strategy evolved, the phenomenon hardly plays a role any more in the maintainance of the fitness and the stability of the population as a whole. Instead, due to 'cultural', often religious prejudices, homosexuals nowadays are treated as belonging to an 'out-group', and discriminated against accordingly.

Honor your father and your mother

While on the one hand there is much mutual love and care in the relationship between parents and their offspring, there may, on the other hand, be also much mutual 'sound and fury', which sometimes is far from 'signifying nothing' (William Shakespeare, Macbeth). Indeed, from conception on, individuals are confronted with parent-offspring conflicts of all kinds. Initially these conflicts concern physiological matters (implantation, nutrition, weaning, etc.), but later in life the accent is on psychological ('you must this', 'you must that', 'don't do that' etc.) and social affairs, and phenomena such as child abuse, infanticide and incest may occur. It is, therefore, certainly not self-evident that children honor their parents. To reinforce their position, parents (societies) may appeal to a 'divine' commandment which helps them make their children suppress any tendency to conflict toward them (and hence to their culture), so that children conform to their parents' norms and values. When such psychological and sociological parent-offspring conflicts are not resolved satisfactorily, it can be suggested, children may (consciously or unconsciously) have aggressive feelings toward their parents: Freud's 'Oedipus complex'. This complex, it is argued, can also be seen as a parent-offspring conflict. Given their biological basis, parent-offspring conflicts can hardly be considered as abnormal. Conflicts between adults and their offspring have always existed and will always exist, simply because it is inherent in our genetic make-up: parents and offspring of sexually reproducing species--humans included--are only about 50% genetically related and hence have different interests at all levels of being. Indeed, parent-offspring conflicts are such stuff as we are made on, and our little life is rounded with its consequences (adapted from William Shakespeare, The Tempest).