AGB 211: Livestock and Poultry Breeding (2+1)

BREEDING FOR HETEROSIS

To exploit heterosis, lines or breeds with good nicking ability or combining ability are crossed. The combining ability can be determined only by test crosses. A breeder attempting to produce lines which will combine well with each other has to produce large no. of lines. Then he can test them in crosses and find those which give best results. This idea is expensive, time consuming and uncertain. As a general rule the lines or breeds totally unrelated give better heterosis in crosses.

There are two types of combining ability

• General combining ability (GCA) is the mean performance of F1 expressed as a deviation from the mean of all crosses and it is due to additive genetic variance.
• Specific combining ability (SCA) is the superiority of a particular cross over the average GCA of the two lines and it is due to non-additive genetic variance.