Glossary Plant Breeding

Single Cross. An F 1 hybrid between two different inbreds. The number of possible
single crosses involving n inbreds will be [n.( n-1 ) / 2 ]. The current trend in breeding
hybrid maize is to develop single cross hybrid as it displays heterosis twice as much
as double cross hybrids.
Single Pod Descent Method. A method of handling segregating generations in which F 2
plants and their progenies are advanced rapidly in succeeding generations by seeds
from a single pod. Evaluation of progeny rows start in F 6 generation. (Also see single
seed descent method).
Single Seed Descent Method (Goulden 1939). A modification of bulk population
breeding in which F 3 and succeeding generations are advanced from single seeds of
each harvested plant of the previous generations followed by progeny evaluation from
F 6 /F 7 . Theobjectiveistomaintainthedescendants from a maximum number of F 2
plants during segregating generations. It is usually accepted that this method is quite
convenient, timesaving, and economical and is able to maintain considerable
variability. However, the inherent drawback attached to this method is that a number
of superior worthwhile genotype may be lost at any stage of advancement.
Single Test. Evaluation of genotypes performed only once. This does not provide an
accurate picture of the genetic variance as it contains various interaction variances in
addition. However, progressively more and more of the interaction variances can be
identified and removed as more and more locations and times are sampled.
Single Factor Experiments. Experiments with varying levels of a single factor while all
others are kept constant. For example, most crop variety trials are single-factor
experiments because the variety is a single factor and the factor levels (that is,
treatments) are the different genotypes/varieties. Only the variety differs from one
experimental plot to another while all management factors are applied uniformly to all
plots.
Sire. Themaleparentinmammals.
Sister Chromatids. Chromatids derived from the same chromosome through duplication.
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