A genetic interaction (GI) between two genes generally indicates that the phenotype of a double mutant differs from what is expected from each individual mutant. In the last decade, genome scale studies of quantitative GIs were completed using mainly synthetic genetic array technology and RNA interference in yeast and Caenorhabditis elegans. These studies raised questions regarding the functional interpretation of GIs, the relationship of genetic and molecular interaction networks, the usefulness of GI networks to infer gene function and co-functionality, the evolutionary conservation of GI, etc. While GIs have been used for decades to dissect signaling pathways in genetic models, their functional interpretations are still not trivial. The existence of a GI between two genes does not necessarily imply that these two genes code for interacting proteins or that the two genes are even expressed in the same cell. In fact, a GI only implies that the two genes share a functional relationship. These two genes may be involved in the same biological process or pathway; or they may also be involved in compensatory pathways with unrelated apparent function. Considering the powerful opportunity to better understand gene function, genetic relationship, robustness and evolution, provided by a genome-wide mapping of GIs, several in silico approaches have been employed to predict GIs in unicellular and multicellular organisms. Most of these methods used weighted data integration. In this article, we will review the later knowledge acquired on GI networks in metazoans by looking more closely into their relationship with pathways, biological processes and molecular complexes but also into their modularity and organization. We will also review the different in silico methods developed to predict GIs and will discuss how the knowledge acquired on GI networks can be used to design predictive tools with higher performances.

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It is shown that the inversion parameter, v, in the cubic spinel (MnvNil-v) [Mnz-vNiv]04 changes from 0.74 when the sample is quenched from a high temperature to 0.93 when slowly cooled. The cell parameter is a linear function of v and is a minimum when v is a maximum; the oxygen positional parameter is independent of thermal treatment. The short range order between nickel and manganese atoms in the B sites was examined and the correlation coefficients were determined. The variation of internal energy as a function of the degree of inversion was also calculated and discussed.

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Structure magn6tique du spinelle antiferromagn6tique ZnFe,O, Par B. BOUCHER, R. Bum') et M. PERRIN~) On a fabriqub et btudib par diffraction de neutrons un 6chantillon de ZnFe,O,. Ce corps est un spinelle normel. A 10,6 O K l'ordre antiferromagnbtique B grande distance s'6tablit. La maille magn6tique (a, a, 2 a ) a un volume double de celui de la maille chimique (a, a, a). Trois mod&les de structures magnbtiques rendent compte des rbsultats expbrimentaux. Les moments sont dirigbs suivant les axes [lo01 et [OlO]. A 4,2 O K le moment magnbtique du Fe3+ est 4,Op~.On dbtermine la variation de la valeur du moment en fonction de la tempbratwe.A sample of ZnFe,O, has been prepared and then studied by neutron diffraction in which a normal cubic spinel structure was found. At 10.6 O K long range antiferromagnetic order occurs. The volume of the magnetic cell (a, a, 2 q) is twice the chemical one (a, a, a). Three models of magnetic structures are in agreement with the experimental results. The magnetic moments lie along the [lo01 and [OlO] axes. At 4.2 OK the FeS+ moment is 4.0 pm A dependence of the magnitude of the magnetic moments with temperature has been obtained.

Pure iron manganite FeMn2O4 was prepared at 1250°C and quenched. It crystallizes in the b.c. tetragonal system D4h19. Neutron diffraction measurements above the Curie temperature (120°C) show that the inversion parameter is 0.91 (nearly inverse spinel). The spontaneous magnetization at 4.2°K measured in high static and pulsed fields is 1.55 μB/mol. The magnetic moment was observed to increase linearly above 70 kOe and showed the presence of a strong anisotropy with easy axis near the [101] direction (unusual fact). Neutron diffraction measurements at 4.2°K lead to the determination of the magnetic structure of FeMn2O4. The tetrahedral sublattice moments (4.3 μB) are collinear in a (010) plane making an angle of − 172° with Ox [100]. Spins in octahedral sites (3.1 μB) are divided into four magnetic sublattices with a pyramidal arrangement whose axis of symmetry lies in the plane (010) and makes an angle of 14° with Ox [100]. At 55°K the spins of the octahedral sublattices become collinear, the easy magnetization direction remaining unchanged up to 310°K where it changes to the [110] direction, the magnetic structure of FeMn2O4 becoming completely collinear.

Mn3O4 is a tetragonal spinel I41/amd. It is ferromagnetic below Tc = 43°K. At 4.2°K neutron diffraction measurements on powdered samples show the presence of 8 sublattices in a unit cell a, 2a, c which is double the chemical unit cell. These 8 sublattices are arranged as follows: 2 sublattices at tetrahedral sites and 6 sublattices at octahedral sites. At 4.2°K the moments are 4.65 μB on A sites and 3.55 μB on B sites with a resulting moment of 1.85 μB/molecule along the (010) direction. The study of thermal variation of the structure shows that at 33°K a rearrangement of moments occurs such that the chemical and magnetic unit cells become identical.

Cobalt manganite CoMn2O4 is prepared at 1250°C and quenched from different temperatures. It always crystallizes in centered tetragonal system but its lattice parameters and inversion degree change by quenching. Measurements of paramagnetic susceptibility above the Curie temperature and magnetization in high fields show the ferrimagnetic behavior of CoMn2O4 with a very weak spontaneous magnetization at 4.2°K. Anisotropy is very strong. The magnetic structure of CoMn2O4 has been worked out from low-temperature neutron-diffraction patterns. In tetrahedral sublattice, spins are collinear, and their mean length is in very good agreement with theory assuming that Co2+ and Mn3+ moments are spin-only ones. In octahedral sublattice, a Yafet-Kittel structure is in very good agreement with experimental results. The B resulting moment is collinear with the A spins along the [110] direction. The net spin value in B sublattice is much smaller than the theoretical one. This low-temperature structure becomes collinear at 70°K.