Glossary Plant Breeding

Pericentric Inversion. An inversion that involves centromere of the chromosome. It
greatly alters the morphology (and hence, arm ratio) of the chromosome. The changed
arm ratio facilitates its easy detection. Like paracentric inversion, crossover types are
not recovered but for a different reason. Recombinants are simultaneously duplicated
(for one part) and deleted (for the other) products. Thus there is selective recovery of
parental types in an inversion heterozygote.
Permissive Conditions. Those environmental conditions under which a conditional
mutant shows the wild-type phenotype.
Ph.D. Doctor (docere: a Latin word, which means to teach) of philosophy (philo +
sophia; the Greek words, which imply love and knowledge, respectively). Thus it
denotes a person having love for knowledge and teaching.
Phenocopy. An environmentally induced phenotype that resembles the phenotype
produced by a mutation. Of course, this effect is not inherited.
Phenotype. A description of all aspects of individual’s morphology, physiology,
behaviour, and its ecological relationships. The phenotype, which is the observable
properties of an organism, is brought about by its genotype in concert with the
environment in which the organism develops. The term has been derived from a
Greek word that literally means “ the form that is shown”. In practice, however, it is
used in a more restricted sense; that is, we say phenotype with respect to a particular
trait. Contrary to genotype, it is a dynamic entity, which changes with time.
Phenotypic Assortative Mating. Mating between individuals which resemble each
other more closely phenotypically than the rest members of the population. The final
result of phenotypic assortative mating amounts to that for genetic assortative mating
so long as heritability is complete (that is , 100 per cent). Under condition of complete
heritability, the rate of approach towards homozygosity gets slower with the increase
in the number of loci involved. When heritability is not complete, 100 per cent
homozygosity is not possible (‘F’ cannot reach unity).
Phenotypic Disassortative Mating. Mating between individuals having contrasting
phenotypic traits. It tends to maintain (or even slightly increase) heterozygosity,
decrease the population variance, and reduce correlation between relatives. It may be
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