Glossary Plant Breeding

individuals. Heterosis is supposed to be the outcome of such genetic organization.
Autogamous species too show heterosis since it has also appreciable level of
heterozygous balance. This balance in self-fertilized species is supposed to be
evolutionary remains of their outbreeding ancestors.
Hexaploid. A cell having six chromosome sets or an organism composed of such cells. If
all the sets are identical, the individual is called an autohexaploid (e.g., sweet potato).
If, however, genomes are only partially homologous, it is referred to as allohexaploid.
Hierarchy. An arrangement into a graded series.
High-Input Agriculture. Agriculture augmented with a variety of inputs, such as
irrigation and improved mechanization, and/ or with such inputs as fertilizers,
pesticides, herbicides, and fungicides. Breeding programmes, in general, have been
very successful and efficient in high-input agriculture (resource rich areas), perhaps
because agricultural conditions in farmers’ fields and agricultural research stations in
which most new varieties are bred and developed are closely similar. Furthermore,
most of the variables of the production environments are predictable and manageable.
High Nutrient Rice. Genetically engineered rice with enhanced iron and cysteine
content. It has a ferritin gene from P. vulgaris, andthermotolerantphytase gene from
A. fumigates.
Histocompatibility Genes. The genes that encode the histocompatibility antigens that in
turn determine the acceptance or rejection of a tissue graft.
Histogenesis. The process of formation and development of tissues; also called
histogeny.
Histone. A type of basic protein that forms the unit around which DNA is coiled in the
nucleosomes of eukaryotic chromosomes. Histones are a group of five basic proteins
that associate with DNA in the cell nucleus to form chromatin.
Holandric Inheritance. A type of inheritance governed by genes completely linked to
the Y-chromosome. Such genes (often called holandric or Y-linked genes) are
transmitted exclusively from father to the sons and thus manifestation is limited to the
male sex only.
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