Apomixis in hawkweed: Mendel's experimental nemesis

Nemesis Reconsidered

The hypothesis of a companion object (Nemesis) orbiting the Sun was motivated by the claim of a terrestrial extinction periodicity, thought to be mediated by comet showers. The orbit of a distant companion to the Sun is expected to be perturbed by the Galactic tidal field and encounters with passing stars, which will induce variation in the period. We examine the evidence for the previously pro...

Medical nemesis?

Nemesis of neglected neurosarcoidosis

Neurosarcoidosis (NS) is diagnosed when noncaseating granulomas develop in the nervous system, often associated with similar pathology in other organs. While lung and skin manifestation are more common, the neurological manifestations including meningitis, parenchymal brain or spinal cord lesions, or cranial or peripheral nerve damage are among the most serious and difficult to treat manifestat...

Apomixis and cassava.

Apomixis means seed formation without fertilization. In cassava (Manihot esculenta) it is an alternative to reproduction by cuttings, which normally transmits pathogens and leads to an accumulation of viral and bacterial diseases. Apomixis also assures preservation of heterosis and avoids genetic segregation. It occurs in wild relatives of cassava and has been transferred successfully from Mani...

Genetic mechanisms of apomixis.

The introduction of apomixis to crops would allow desirable genotypes to be propagated while preventing undesirable gene flow, but so far there has been little success in transferring this trait from a natural apomict to another species. One explanation is the sensitivity of endosperm to changes in relative maternal and paternal contribution owing to parental imprinting, an epigenetic system of...