Pleiotropy-A single gene that has an effect on the expression of two or more phenotypic traits is said to have a pleiotropic effect- on the traits. For example, testosterone controls the development of what are referredto as secondary sexual characteristics, but testosterone also relates to behavioral traits like aggression. Thus, a gene that controls the level of testosterone would have a pleiotropic effect on the expression of many secondary sexual traits which are morphological, as well as behavioral
2. Polygenic Iftwo or more genes are responsible for a single trait, the phenotypic trait is said to be governed by polygenic factors. For example, growth rate is undoubtedly caused by a number of genes that act in a complex cascade.
3. Mendelian inheritcance : It states the following :
(a) Law of Dominance
(i) Characters are controlled by discrete units called factors.
(ii) Factors occur in pairs.
(iii) In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive).
(b) Law of segregation:Aeles do not show any blending and both the charactors are recovered in `F_2` generation though one of these is not seen at the `F_1` stage.
(c) Law of independent assortment: When two pairs of traits are combined in a hyhrid, segregation of one pair of characters is independent of the other pair of characters.
(b) See point 2., Polygenic inheritance [above]. .
