This document discusses combining ability, which refers to an individual's ability to transmit superior performance to its offspring. There are two types of combining ability: general combining ability (GCA) and specific combining ability (SCA). GCA is due to additive genetic effects and relates to an individual's average performance across hybrid combinations. SCA is due to non-additive genetic effects like dominance and epistasis and relates to performance in specific hybrid combinations. The concepts of GCA and SCA were introduced in corn breeding and have been applied to animal breeding as well. Progeny testing is used to examine combining ability.

1. Parvati Tamrakar
M.Sc. FGR 3rd Sem
G.G.V. Bilaspur

2.  Certain inbreed lines will display hybrid vigor
when crossed. These vigor lines are said to
have favorable combining ability.
 Combining ability is the capacity of an
individual to transmit superior performance
to its offspring.
 It is the phenomenon with which the inbreed
lines when crossed give rise to hybrid vigor.
 It is examined by progeny testing.

3.  Two types of combining ability, general (GCA)
and specific (SCA), have been recognized in
quantitative genetics.
 The concepts of general combining ability
(GCA) and specific combining ability (SCA)
were first introduced by in relation to corn
breeding and have been expanded into
animal breeding by others.
◦ Certain inbreeds which have the ability to combine
well with testers have general combining ability
(GCA).
◦ The inbreeds combines well only in certain crosses
have specific combining ability (SCA) .

4.  The term GCA is used to designate the
average performance of an inbred line in
hybrid combinations.
 Featues of GCA:
◦ GCA is due to genes which are largely additive in
their effects. It is due to additive genetic variance
and additive x additive gene interaction.
◦ It denotes combining ability of genotype especially
with other testers.
◦ It helps in identification and selection of best
genotype to use it in hybridization as a parent.
◦ It is estimated by half-sib mating.
◦ It have relationship with Narrow sense Heritability.

5.  First Year
◦ Superior plants for the character under
improvement are selected from the base
population.
◦ The selected plants are selfed and also crossed with
heterozygous tester having broad genetic base.
◦ The selfed seed is kept storage.
 Second Year
◦ The crossed seed is sown and the combining ability
selected plants is evaluated and plants with good
GCA are identified.

6.  Third Year
◦ The progeny of selected plants with good GCA are
grown from their selfed seed is kept in cold
storage.
◦ These progenies are inter mated in all possible
combinations and their crossed seed is composited
to form a new source of population for further
selection.
◦ This complete original selection cycle. Many such
cycles may be made to obtain desired results.
 Main features of this method to use for
genetic improvement of quantitative
characters in which selection is made or the
basis of test crosses performance.
 This method also used for providing good of
population and required three season or year

7.  SCA is used to designate those cases in which
certain combinations do relatively better or worse
than would be expected on the basis of the
average performance of the lines involved.
 SCA is due to genes with dominance or epistatic
effect.
 Features of SCA:
◦ It represents deviation from gca.
◦ It is due to dominance genetic variance and all the three
types of gene interactions.
◦ It helps into identification and hence the selection of
best cross combinations i.e. those with the desired
output.

8. ◦ When we see that a inbred line combines well in any
cross, it is due to specific combining ability.
◦ It is estimated by full sib mating.
◦ It have a relationship with heterosis.

9.  First Year
◦ Several plants are selected and selfed.
◦ The selected plant (male) are also crossed to an tester
(female).
 Second Year
◦ R.Y.T is conducted using test cross progeny.
◦ Outstanding progenies are identified.
 Third Year
◦ Selfed seeds from the progeny are planted in separate
progeny row in a crossing block.
◦ All possible inter cross are made by hand among
progeny.
◦ Equal amount of seed is composited.
◦ This complete the original selection cycle.

10.  Fourth Year
◦ The combination seed is planted and operation of
1st year repeated.
 Fifth Year
◦ Second year operation repeated.
 Sixth Year
◦ Third year operation repeated.