Glossary Plant Breeding

some characters. For instance, if we cross aaBB and AAbb, we are likely to get AABB
and aabb in F 2 generations. These genotypes may have enhanced or retarded
phenotypic expressions compared to their parents.
Transient Diploid. The stage in the life cycle of predominantly haploid fungi (and algae)
during which meiosis occurs.
Transition. A type of nucleotide-pair substitution involving the replacement of a purine
with another purine (adenine with guanine or vice-versa) or of a pyrimidine with
another pyrimidine (cytosine with thymine or vice-versa). This substitution may occur
due to a spontaneous error or mispairing between base pairs under the influence of a
physical or chemical mutagen. It ultimately results in mutation (GC → AT transition,
for example).
Translation. The ribosome-mediated production of a polypeptide whose amino acid
sequence is derived from the codon sequence of an mRNA molecule.
Translocation. The change in the position of a segment of a chromosome to another
location in the same or a different chromosome; the relocation of chromosome
segment in a different position in the genome. If in the same chromosome, it is called
simple translocation.
Transmission Genetics. The study of the mechanisms involved in the passage of a gene
(and thus a trait) from one generation to the next.
Transpiration Efficiency. The ratio of growth (net production) and water transpired
usually expressed as grams of dry matter produced per 1000 grams of water
transpired. Most species of agricultural crops have transpiration efficiency of 2 or
less. However, drought resistant crops, such as sorghum/ millets may have
efficiencies of 4.
Transposable Genetic Element. A general term for any genetic unit that can insert into a
chromosome, exit, and relocate. It includes insertion sequences, transposons, some
phages, and controlling elements.
Transposition. The transfer of a chromosome segment to another position owing to
intra- or interchromosome structural changes. See translocation/ shift.
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