Hayes and Garber - Cucurbit Breeding

Mutant.
that of its
DEFINITIONS 297
An individual possessing a genotypic character differing from
parent or those of its parents, and not derived from them by a
normal process of segregation.
Mutate. To undergo a change in genotypic character independently of
normal segregation.
Ovule. Female sex cell with its immediate surrounding parts.
Ovum. Egg cell.
PI, P2, etc. The 1st, 2nd, etc. generation of the parents.
Palea. The upper of the two bracts immediately enclosing each floret in
grasses.
Panicle.
and irregular, as in oats, rye, proso, etc.
A compound inflorescence with pediceled flowers usually loose
Pedicel. A stalk on which an individual blossom is borne.
Peduncle. The primary stalk supporting either an inflorescence or a
solitary flower. In grasses the uppermost internode of the culm.
Pericarp. The matured wall of the ovary.
Phenotype. The apparent type of an individual or group of individuals,
i.e. the sum of the externally obvious characteristics which an individual
possesses, or which a group of individuals possess in common; contrasted
with genotype.
Presence and Absence Hypothesis. The hypothesis that any simple
Mendelian difference between individuals ,
results solely from the presence
of a factor in the genotype of the one individual, which is absent from that of
the other.
Presence and absence of unit-differences as a convenient method
of describing the results of genetic experiments should be carefully distinguished
from the presence and absence hypothesis. The method is purely
objective and entirely free from hypothetical implications.
Probable Error. A measure of accuracy for results obtained by statistical
methods. The chances are even that the true value lies within the limits
marked by the probable error.
Probable Error of a Single Determination. S. D. X 0.6745.
Probable Error of a Difference. The square root of the sum of the
squares of probable errors of the two results, or the probable error of a
single determination multiplied by the \/2.
Pubescent. Hairy in a general sense; in special use, covered with short,
soft hairs.
Pure Line. A group of individuals derived solely by one or more selffertilizations
from a common homozygous ancestor. Sometimes erroneously
applied to groups of individuals believed to be genotypically homogeneous
(a homozygous biotype or a clone) without regard to the method of
reproduction.
Recombination.
Union of parental factors in individuals of the second or
later generations after a cross.
Reduction Division. That in which homologous chromosomes separate
preparatory to formation of gametes.
Repulsion. Such a relation between two genetic factors that both are
not, as a rule, included in the same gamete, referring especially to cases in
which the factors in question give rise to obviously different characteristics;
also called "spurious allelomorphism."