8,003 research outputs found
Technique for abrasive cutting of thick-film conductors for hybrid circuits
Abrasive jet technique, producing prototype conductor networks for thick-film hybrid microcircuits, does not require screening and fixing procedures. Pantograph engraver is used to perform abrasive cutting of the conductor network
Evolution of flowers and inflorescences
Plant development depends on the activity of meristems
which continually reiterate a common plan. Permutations
around this plan can give rise to a wide range of morphologies.
To understand the mechanisms underlying this
variation, the effects of parallel mutations in key developmental
genes are being studied in different species. In
Antirrhinum, three of these key genes are: (l)floricaula ffio)
a gene required for the production of flowers (2) centror&-
dialis (cen), a gene controlling flower position (3) cycloidea
(cyc), a gene controlling flower symmetry. Several plant
species, exhibiting a range of inflorescence types and floral
symmetries are being analysed in detail. Comparative
genetic and molecular analysis shows that inflorescence
architecture depends on two underlying parameters: a
basic inflorescence branching pattern and the positioning
of flowers. Theflo and cen genes play a key role in the positioning
of flowers, and variation in the site and timing of
expression of these genes, may account for many of the
different inflorescence types. The evolution of inflorescence
stiucture may also have influenced the evolution of floral
asymmetry, as illustrated by the cen mutation which
changes both inflorescence type and the symmetry of some
flowers. Conflicting theories about the origins of irregular
flowers and how they have coevolved with inflorescence
architecture can be directly assessed by examining the role
of cyc- and cen-like genes in species displaying various
floral symmetries and inflorescence types
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