The causal sequence of meiosis
• . i . • pro6eeds"., and where crossing-over takes place. These prime wriables ..at6 ghe.eontaet-point, the th~e-lhnit of pairing and. the torsion in paired regions. Their action has been inferred from the comparison of pairing in ~dated forms witt{ variabie pairmg frequencies and ohiasma distribution ; from ~he pa.h-ing in hybrids, mutants and po]yploids; and h'om the ~ifieiaI !n}errnption of normal pairing. Suc]a comparisons have to be m~de ~vifla even ~ea te r accuracy and detgii if gee theory of meiotic p~mng.as to be ~ested and consolidated. The time has now arrived for an exac$ definitio~ of the individual aoti.ons and of the interactions of the t~{'egva.riables and of {Heir effect onohiasma formatim.~. k it}~iJ.y of pagfing variM;ion rest~Ith~g from genetic aad :from en~dr0nmental Souzces, i o an interspeeitie eo.mparison wibh varied environmental eoi~Ntigns,i.forms ~ahe most promising approach. ~,r,gt~igcvria., which h.a,s proved such Useful material in the discovery of ~he ele.me~lts o:[ mitosis and . . . . meiosis, is eminent.]y st~ita, ble :for further ana.].gsis} :[or the following rea.soJ.is:
The origin of iso-chromosomes
SummaryFollowing misdivision of the centromere at meiosis in diploid and triploidFritillaria new telocentric chromosomes are formed whose broken ends rejoin within the centromere. This type of chromosome is delayed at metaphase and anaphase in the pollen-grain mitosis. It may then, either break again at the centromere, or pass without separation to the pole as a new iso-chromosome.The misdivision and the origin of the iso-chromosome are each likely to be important as affecting the genetic structure of the chromosome and the mechanical properties of the centromere.
Remote estimation of nitrogen and chlorophyll contents in maize at leaf and canopy levels
a b s t r a c t Leaf and canopy nitrogen (N) status relates strongly to leaf and canopy chlorophyll (Chl) content. Remote sensing is a tool that has the potential to assess N content at leaf, plant, field, regional and global scales. In this study, remote sensing techniques were applied to estimate N and Chl contents of irrigated maize (Zea mays L.) fertilized at five N rates. Leaf N and Chl contents were determined using the red-edge chlorophyll index with R2 of 0.74 and 0.94, respectively. Results showed that at the canopy level, Chl and N contents can be accurately retrieved using green and red-edge Chl indices using near infrared (780-800 nm) and either green (540-560 nm) or red-edge (730-750 nm) spectral bands. Spectral bands that were found optimal for Chl and N estimations coincide well with the red-edge band of the MSI sensor onboard the near future Sentinel-2 satellite. The coefficient of determination for the relationships between the red-edge chlorophyll index, simulated in Sentinel-2 bands, and Chl and N content was 0.90 and 0.87, respectively.