Biometrics is the science dealing with statistical analysis of biological problems. Quantitative genetics studies inheritance of quantitative traits using statistics. The two requirements for plant breeding are genetic variation and exploiting that variation through selection. Phenotype is influenced by both heritable (genetic) and non-heritable (environmental) factors. Quantitative traits are more influenced by environment and genetic background than qualitative traits. The relationship between genotype and phenotype for quantitative traits is partially hidden by environmental effects.

1. BIOMETRICS – COMPONENTS OF GENETIC VARIATION
Biometry or biomatrics is the science thatdeals with the application of statistical procedures
to the study of biological problems.
Biometrical genetics or Quantitative genetics is that branch of genetics, which attempts to
unravel the inheritance of quantitative traits using statistical concepts and procedure.
INTRODUCTION :
The two basic requirements of Plant Breeding are the presence of genetic variation
and exploitation of this variation through selection. The selection of plants from a population
is almost always based on their phenotype. Phenotype has both heritable and nonheritable
components. The heritable component is due to the genes present in plants, that is genotype.
The non-heritable component consists of the effects of environment. The value of progeny
obtained from a selected plant, therefore, would largely depend upon therelative contributions
by the heritable and the non-heritable components to its phenotype., clearly, the breeder
should be thoroughly familiar with the laws of inheritance and the relative importance of the
genotype and the environment in determining the concerned phenotype.
Qualitative and Quantitative characters :
Some characters are little affected by other genes, i.e. the genetic back ground, or the
environment. Such characters are generally governed by one or few genes with large, easily
detecta ble effects, such genes are known as oligogenes. The characters produced by
oligogenes show distinct classes and are known as qualitative characters or olygogenic
traits. On the other hand, the development of many characters is very much affected by the
genetic background and, more particularly, by the environment. These characters are
governed by several genes with small individual effects; these genes one known as
polygenes. The characters produced by polygenes are referred to as quantitative
characte rs, because they do not show clear -cut classes and have to be studied by
measurement. They are also called Polygenic traits since they are governed by polygenes.
The inheritance of both qualitative and quantitative characters follows the laws of Mendel.
But the effects of individual genes in the two cases are totally different in magnitude
consequently, the techniques used to study the two types of characters are also different.
Role of the environment in Quantitative Inheritance
Quantitative characters are considerably affected by environment. The main result of this
effect is that the relationship between genotype and phenotype is partially or completely
hidden i.e. the phenotype doesnot reveal the genotype.
For eg: Phenotype = Genotype+ Environment P=G+E
If environment = 0 then phenotype = Genotype. However the effect of environment
is seldem zero. So phenotype is the joint action of Genotype and Environment.
In crop improvement, the breeder selects plants on the basis of their phenotype.
The effectiveness of selection depend on the proportion of phenotype due to the genotype.
Therefore, it is important to know the extent to which environment influences different

2. quantitative characters.
To estimate the effect of environment on a character, large No. of strain / genotypes are
grown in a replicated trial and the data is subjected to analysis of variance as per the
experimental design used.
The genotype x Environmental interaction signifies that the relative performance of various
genotype in effected by the environment. For eg: Performance of genotype ‘A’ may be
superior to the genotype ‘B’ in one environment but in another environment inferior to that of
‘B’
If G X E interaction is absent, genotype ‘A’ will be superior ‘B’ in all the environments.
artificial selection plays an important role.