E A Stark | PubMed Health

PubMed1996

Molecular analysis of the structure of the maize B-chromosome.

The overall composition of the maize B is similar to that of the standard chromosome complement (A-chromosomes). This has been demonstrated by the use of several methods including: (a) genomic in situ hybridization (GISH), (b) analysis of highly repetitive sequences by the comparison of restriction digests of 0B and +B DNA and (c) the characterization of middle-repetitive cloned sequences. By the use of the technique of random amplification of polymorphic DNA-polymerase chain reaction, we have identified a B-specific repetitive sequence family. Sequence analysis of the B-specific clone reveals a relationship to the PREM-1 family of maize retroelements, which are preferentially transcribed in pollen. These results suggest an internal origin of the B-chromosome from within the maize genome, but demonstrate also that specific sequences can evolve by rapid processes of genomic turnover. Models for the origin of the maize B are discussed in the context of the present data.

Base Sequence↗

PubMed1982

Simulation technology and the fixation phase.

Continuing advances in simulator technology have produced almost totally real instrument and aural cue systems, and a number of specialized G-cuing systems are rapidly being matched to the sensory capabilities and needs of flight crews. Intensive research in visual cuing is providing more and more realistic visual scenes and, in general, flight simulators are becoming more real, more complex, and more expensive. It is suggested that Fitts' "fixation" phase of skill acquisition does not require a flight environment, or even a reproduction of the flight environment, for effective learning and transfer. While similarity between training and operational environments appears to be essential for transfer of training to take place, the concept of similarity may not include the total complex of stimuli available in flight as perceived by the instructor or the simulator designer, but may include only the stimuli perceived by the student as he observes, practices, and validates specific tasks within the period of response fixation. It is suggested that special attention be given to the task information required and the learning functions involved in the fixation phase of skill learning.

Aerospace Medicine↗