Glossary Plant Breeding

Two Stage Testing (Hanson and Brim 1963). A scheme for evaluation of advance
generation homozygous lines (F 6 /F 7 ) which involves testing of all lines in one or two
environments and selecting better performing lines for retesting in a number of
environments. The two stage-testing programme is more efficient than testing all the
lines in one or two environments. The use of two locations for the first stage test
provides an insurance against abnormal conditions or seasonal hazards.
Two-factor Cross. A genetic recombination experiment involving two genetic markers
(a+b+/ab).
Two-factor Experiments. Biological experiments that deal with two variables while
keeping constant all other factors. Thus when response to the factor of interest is
expected to differ under different levels of the other factors, factorial experiments are
designed to handle simultaneously two or more factors.
Type Number. The most frequently occurring chromosome number in a particular
taxonomic group (modal number). The term is often used with the implication of its
being the ancestral number of the group in question. Other numbers are then assumed
to be derived from the type number.
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