Glossary Plant Breeding

x. Basic number of chromosomes in a polyploid series; the smallest number of
chromosomes in a chromosome set.
X 1 , X 2 , X 3 . Symbols used to denote first, second, third… generations from an irradiated
ancestral plant (X 0 ).
X Chromosome Inactivation. The process by which the genes of an X chromosome in a
mammal can be completely repressed as a part of the dosage compensation
mechanism. Such an inactivated chromosome is referred to as a Barr body.
X Linkage. The association of genes present on an X chromosome (but not on the Y).
X–and–Y Linkage. The inheritance pattern of genes found on both the X and Y
chromosomes.
X-ray Crystallography. A technique for deducing molecular structure by aiming a beam
of x-rays at a crystal of the test compound and measuring the scatter of rays.
X-ray Diffraction. Scattering of x-rays by the atoms of a crystal in a manner such that
the resulting diffraction pattern provides information about the structure and/or
identity of the substance.
Xenia. Effect of pollen on the embryo and endosperm.
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Y Linkage. The inheritance pattern of genes found on the Y chromosome. Thus far, only
a few genes have been reported to have their association on the Y chromosome.
Yield. A measure of the relative reproductive capacity of an individual or a genotype.
ZTest.A statistical test of significance for difference between means of large samples
(>30). It is supposed that z-test is not affected by sampling error that must remain in
the estimation of population standard deviation due to small size of samples in t-test.
Zein. The main protein of Indian corn present in the endosperm portion of the seed.
Zero Selection. Highest selection pressure such that zero per cent individual is selected,
that is, 100 per cent individuals are rejected (selection intensity is most stringent, that
is zero).
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