Glossary Plant Breeding

large (40) and the experimental area has a predictable productivity gradient.
However, if becomes necessary, larger number of treatments can be included at the
cost of reducing plot size for each entry within the blocks.
Randomization. Random assignment of treatments to experimental plots. It ensures that
each entry or treatment will have an equal chance of being assigned to any
experimental plot, and consequently of being grown in any particular environment
existing in the experimental site. In essence, it is a technique to obtain an unbiased
estimate of experimental error.
Range. The simplest measure of dispersion. It is the difference between the largest (L)
and the smallest (S) of observations and provides, at least, some idea of the amount of
variability present. It is affected by fluctuations of sampling and is completely
unrelated to any type of frequency distribution. It is unit-dependent and expressed in
the unit of scale of measurement. Thus it cannot be used to compare variability of two
different traits. To make it comparable, a similar statistic called Range Coefficient
[(L-S)/(L+S)] is used.
RAPD. Randomly Amplified Polymorphic DNA; a set of several genomic fragments
amplified by single PCR primer. It is somewhat variable from individual to
individual. Heterozygotes (+ / -) for individual fragments can act as markers in
genome mapping.
Raphanobrassica (Karpechenko 1928). The classical allopolyploid synthesized by
making a cross between Brassica and Raphanus spp. The objective was to combine
the leaves of cabbage (Brassica) and the roots of radish (Raphanus). However, the
result came out to be just reverse. This clearly showed difficulty in predicting the
precise combination of parental characteristics that would appear in ensuing alloploid.
Reaction Norm. The range of phenotypic reactions of a genotype as manifested by the
variety of phenotypes that the specific genotype is able to produce in response to
environmental influences.
Reading Frame. The codon sequence that is determined by reading nucleotides in groups
of three from some specific start codon.
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