Glossary Plant Breeding

evolutionary terms, it is possible that a symbiotic relationship could have evolved into
the present situation, in which these organelles have only a certain degree of
autonomy.
Symbiosis. A kind of inter-species interaction in which both the interacting partners
benefit from each other. Symbiosis literally means living together. Contrary to
protocooperation, this kind of interaction is obligatory, Rhizobium-legume
association, for example. Instances of mutualism (symbiosis) are more likely to
develop between organisms with widely different requirements whereas organisms
with similar needs are more likely to get involved in competition. Each step of
symbiosis is controlled and/or influenced genetically.
Sympatric. Of two or more populations occupying the same geographical area. Such
populations may remain completely separated by different habitat preferences, or by
different habits.
Sympatric Species. Species formation in the absence of geographical isolation by
acquiring mechanisms of reproductive isolation within a panmictic unit.
Syn-0, Syn-I, Syn-II. Symbols for designating the original synthetic population, first
synthetic generation (progeny of Syn-0), and second synthetic generation (progeny of
syn-I)
Syn-II Generation. The panmictic generation following synthesis by crossing a number
of lines having proven combining ability (analogous to F 2 generation).
Synapsis. Close-pairing (point-to-point pairing) between homologous chromosomes at
zygotene sub-stage during meiosis I.
Synaptic Genes. Genes influencing the extent of meiotic pairing.
Synaptonemal Complex. A complex structure that unites homologs during prophase of
meiosis-I. A protein plus a small amount of DNA constitutes the complex structure.
Syncytium. A single cell with many nuclei.
Syndrome. A set of specific characteristics (symptoms) of an abnormal genetic
condition. A genetic syndrome may be transmitted to the offspring as a unit.
Syngamy. Sexual reproduction; the union of male and female gametes leading eventually
to zygote formation.
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