Biomass determination.

The reasons for and historical backgrounds of biomass determination are discussed under the aspects of theoretical and practical importance, usefulness and representativity. Off-line methods are evaluated and compared with on-line methods; constraints of applications and conclusiveness of results are rated. Special emphasis is given to the fact that mere knowledge of a bio-mass concentration is not sufficiently valuable to learn more about physiology nor to determine the effectiveness of a biotechnological process. A combination of several different alternative measuring principles in parallel as well as the exploitation of software sensors is proposed as a promising future solution.     

Sample size determination

Scientists who use animals in research must justify the number of animals to be used, and committees that review proposals to use animals in research must review this justification to ensure the appropriateness of the number of animals to be used. This article discusses when the number of animals to be used can best be estimated from previous experience and when a simple power and sample size calculation should be performed. Even complicated experimental designs requiring sophisticated statistical models for analysis can usually be simplified to a single key or critical question so that simple formulae can be used to estimate the required sample size. Approaches to sample size estimation for various types of hypotheses are described, and equations are provided in the Appendix. Several web sites are cited for more information and for performing actual calculations     

Bird sex determination

During the evolution, sex determination occurred early. Sex determining factors were progressively isolated from other genes in sexual chromosomes, or gonosomes. Among vertebrates, evolution took two opposite pathways : in mammals, the system of XX:XY sex determination, with Y chromosome, induces male differentiation. In contrast, in birds, the system ZZ:ZW, with the W chromosome, induces female differentiation. But comparative studies show that the two pathways are not so simple. In the chicken as in the lower vertebrates, estrogens play a central role in gonadal sex differentiation. Several genes, show to be critical for mammalian determination, are also expressed in the chicken but their expression pattern differs, indicating functional plasticity. The W-linked female determinants remains still unknown. But comparative studies of the two pathways, with conserved and divergent elements, are broadening our understanding of sex determination.