Glossary Plant Breeding

Heteroduplex. A DNA double helix formed by annealing single strands from different
sources. If there is a structural difference between the strands, the heteroduplex may
show such abnormalities as loops or buckles.
Heterogametic Sex. The sex having heteromorphic sex chromosomes (XY, for example)
and thus producing two different kinds of gametes with respect to the sex
chromosomes.
Heterogeneity. A description of the state of a population containing a number of pure
lines or genetically different individuals (in case of a random mating population).
Heterogeneity in such a population (especially in selfers) often leads to: (a)
phenotypic interactions providing gains in performance, and (b) mutual buffering or
homeostasis resulting in steadier performance. Therefore, such a population is
expected to contain cooperative or synergistic neighbours (genotypes). In other words,
heterogeneity in this kind of population is favoured for synergistic genotypes.
Heterogeneous Nuclear RNA. Assortment of RNA types found in the nucleus, including
mRNA precursors and other types of RNA. It is designated as HnRNA.
Heterokaryon Test. A test for cytoplasmic mutations, based on new associations of
phenotypes in cells derived from specifically marked heterokaryons.
Heteromorphic Chromosomes. A chromosome pair with some homology but differing
in size, shape, or staining properties.
Heteromorphic Incompatibility. An incompatibility system which operates through
differences in the morphology of flowers on different plants coupled with sporophytic
control of incompatibility reaction of the pollen. The best-known case is found in
Primula species; however, it is practically unimportant in higher plants.
Heteromultimer. A protein consisting of at least two polypeptide subunits, with at least
two of the subunits being nonidentical (e.g., haemoglobin).
Heteroplasmon. A cell containing a mixture of genetically different cytoplasms and
generally different mitochondria or different chloroplasts.
Heteroploidy. A condition of deviation from the normal chromosome number by a few
chromosomes (2n ± a few chromosomes).
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