Introduction

• 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 detectable effects, such genes are known as oligogenes.
• The characters produced by oligogenes show distinct classes and are known as qualitative characters or oligogenic traits.
• 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 characters, 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.