Glossary Plant Breeding

D 2 -Statistic (Mahalanobis 1928). A statistic used to determine the degree of divergence
among populations/ breeding lines/ genotypes in terms of generalized group distance.
Numerically, it is the sum of squares of differences between any two-populations/
genotypes for each of the uncorrelated variables/traits. (Correlated variables are
transformed to uncorrelated ones by pivotal condensation method). It is useful in
Plant Breeding as it facilitates in making choice of divergent parents for hybridisation
purposes.
Dalton. A unit of molecular weight. One Dalton equals one-twelfth the mass of C 12 .
Darwinian Fitness. The relative probability of survival and reproduction for a genotype;
also called biological fitness or fitness.
Darwinism. Evolutionary concept (descent with modification) as propounded by Charles
Darwin. The four main premises are: (a) life is constantly changing, and all forms of
organisms are transformed over time, (b) all organisms evolved from a common
ancestor, (c) species multiply by splitting into descendent sibling species when
isolated in geographically or ecologically divergent space, and (d) changes occur
gradually over time. Evolution under Darwinian and Mendelian principles is
essentially a two phase process: (i) production of variation, and (ii) biological fitness
of variants in the struggle for existence.
Daughter Cells. Two identical cells formed by asexual division of a cell.
Daughter Chromosomes. The sister chromatids at the anaphase of mitosis or anaphase-II
of meiosis.
Dee-geo-woo-gen. A semi-dwarf variety of rice discovered inTaiwan. Itwassemi-dwarf,
stiff strawed, erect leafed and high yielding. The semi-dwarf trait appears to be
monogenic recessive (sd 1 ). The gene reduces plant height; however, it does not reduce
panicle length.
Deep Water Rice. Rice grown in varying depths of water (1.0-5.0 metres). Such rice
varieties are usually photosensitive. Two independent recessive genes (duplicate
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