Chapter 9 Gene Drive Strategies for Population Replacement

Gene drive systems are selfish genetic elements capable of spreading into a population despite a fitness cost. A variety of these systems have been proposed for spreading disease-refractory genes into mosquito populations, thus reducing their ability to transmit diseases such as malaria and dengue fever to humans. Some have also been proposed for suppressing mosquito populations. We assess the alignment of these systems with design criteria for their safety and efficacy. Systems such as homing endonuclease genes, which manipulate inheritance through DNA cleavage and repair, are highly invasive and well-suited to population suppression efforts. Systems such as Medea, which use combinations of toxins and antidotes to favor their own inheritance, are highly stable and suitable for replacing mosquito populations with disease-refractory varieties. These systems offer much promise for future vector-borne disease control

Sequence Expression of Supernumerary B Chromosomes: Function or Fluff?

B chromosomes are enigmatic heritable elements found in the genomes of numerous plant and animal species. Contrary to their broad distribution, most B chromosomes are non-essential. For this reason, they are regarded as genome parasites. In order to be stably transmitted through generations, many B chromosomes exhibit the ability to "drive", i.e., they transmit themselves at super-Mendelian frequencies to progeny through directed interactions with the cell division apparatus. To date, very little is understood mechanistically about how B chromosomes drive, although a likely scenario is that expression of B chromosome sequences plays a role. Here, we highlight a handful of previously identified B chromosome sequences, many of which are repetitive and non-coding in nature, that have been shown to be expressed at the transcriptional level. We speculate on how each type of expressed sequence could participate in B chromosome drive based on known functions of RNA in general chromatin- and chromosome-related processes. We also raise some challenges to functionally testing these possible roles, a goal that will be required to more fully understand whether and how B chromosomes interact with components of the cell for drive and transmission

Geometrical effects on energy transfer in disordered open quantum systems

We explore various design principles for efficient excitation energy transport in complex quantum systems. We investigate energy transfer efficiency in randomly disordered geometries consisting of up to 20 chromophores to explore spatial and spectral properties of small natural/artificial Light-Harvesting Complexes (LHC). We find significant statistical correlations among highly efficient random structures with respect to ground state properties, excitonic energy gaps, multichromophoric spatial connectivity, and path strengths. These correlations can even exist beyond the optimal regime of environment-assisted quantum transport. For random configurations embedded in spatial dimensions of 30 A and 50 A, we observe that the transport efficiency saturates to its maximum value if the systems contain 7 and 14 chromophores respectively. Remarkably, these optimum values coincide with the number of chlorophylls in (Fenna-Matthews-Olson) FMO protein complex and LHC II monomers, respectively, suggesting a potential natural optimization with respect to chromophoric density.Comment: 11 pages, 10 figures. Expanded from the former appendix to arXiv:1104.481

Magnetsko-optička svojstva legure In1−xGaxP

The room-temperature dependence on composition of the energy gap is measured for the ternary alloy system In1−xGaxP semiconductors. The cross-over point from the direct to indirect optical transition energy gap is found at x = 0.718. An empirical relation for the alloy system energy-gap dependence is found for both direct and indirect transition regions. From the empirical relations belonging to the direct region transition, the values of the expected indirect energy transition at Γc1 are calculated. The difference between these values and the corresponding indirect energy (Γc1−Xc1) are also calculated. The change of Eg due to the effects of magnetic field up to 1.6 T (Tesla) was also measured. The magnetic coefficient is found to be between 3.33×10−7 and 3.87×10−7 eV/T for x = 0.31 to x = 1. A clear deviation of the magnetic coefficient occurred for the change from the direct-region to that of the indirect-region transition.Mjerili smo ovisnost energijskog procijepa u trojnom sustavu poluvodičke legure In1−xGaxP na sobnoj temperaturi. Našli smo prijelaznu točku od izravnih k neizravnim optičkim prijelazima za x = 0.718. Izveli smo iskustvenu ovisnost energijske ovisnosti energijskog procijepa tog sustava za izravne i neizravne prijelaze. Na osnovi iskustvene ovisnosti za područje izravnih prijelaza izračunali smo energiju neizravnih prijelaza za Γc1. Izračunali smo također razlike tih vrijednosti koje odgovaraju energiji neizravnih prijelaza (Γc1−Xc1). Promjene Eg zbog učinaka magnetskog polja mjerili smo do 1.6 T. Našli smo magnetski koeficijent između 3.33 × 10−7 i 3.87 × 10−7 eV/T za x = 0.31 do x = 1. Opaža se jasan otklon magnetskog koeficijenta pri prijelazu od izravnih k neizravnim prijelazima

Bimodality in low-luminosity E and S0 galaxies

Stellar population characteristics are presented for a sample of low-luminosity early-type galaxies (LLEs) in order to compare them with their more luminous counterparts. Long-slit spectra of a sample of 10 LLEs were taken with the ESO New Technology Telescope, selected for their low luminosities. Line strengths were measured on the Lick standard system. Lick indices for these LLEs were correlated with velocity dispersion (σ), alongside published data for a variety of Hubble types. The LLEs were found to fall below an extrapolation of the correlation for luminous ellipticals and were consistent with the locations of spiral bulges in plots of line strengths versus σ. Luminosity weighted average ages, metallicities and abundance ratios were estimated from χ2 fitting of 19 Lick indices to predictions from simple stellar population models. The LLEs appear younger than luminous ellipticals and of comparable ages to spiral bulges. These LLEs show a bimodal metallicity distribution, consisting of a low-metallicity group (possibly misclassified dwarf spheroidal galaxies) and a high-metallicity group (similar to spiral bulges). Finally, they have low α-element to iron peak abundance ratios indicative of slow, extended star formation