Presentation on gca and sca

Presentation on gca and sca

1. Presentation on GCA and SCA

2. Introduction: Combining ability in crosses is defined as the ability of parents to combine amongst each other during the process of fertilization so that favourable genes or characters are transmitted to their progenies. 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 and others

3. The term GCA is used to designate the average performance of an inbred line in hybrid combinations 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. According to GCA is due to genes which are largely additive in their effects and SCA is due to genes with dominance or epistatic effect .

4. Feature of General Combining Ability It is due to additive genetic variance and additive x additive gene interaction. It denotes combining ability of genotype esp. inbred with various testers. Helps in identification and selection of best genotype to use it in hybridization, as a parent. Estimated by half sib mating Have relationship with narrow sense heritability

5. Procedure for estimating and utilizing General Combining Ability (GCA): 1 ) First Year: Superior plants for the character under improvement are from the base population. The selected plants are selfed and also crosses heterozygous tester having broad genetic base. The selfed seed is kept storage.  2) Second Year: The crossed seed is sown and the combining ability selected plants is evaluated and plants with good GCA are identified.

6. Cont.. 3) Third Year: The progeny of selected plants with good GCA are grown from their selfed seed 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 for completion of each cycle.

7. Features of Specific Combining Ability It represents deviation from gca . It is due to dominance genetic variance and all the three types of gene interactions Helps into identification and hence selection of best cross combinations i.e. those with the desired output. When we see that a inbred line combines well in any cross, it is due to specific combining ability. Estimated by full sib mating Have relationship with  heterosis

8. Procedure for estimating and utilizing special combining activity(SCA) 1) First Year: Several plants are selected and selfed . The selected plant ( male) are also crossed to an tester( female).    2 ) Second Year: R.Y.T is conducted using test cross progeny. Outstanding progenies are identified. 3 ) Third Year: Selfed seed 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

9. Cont. 4) Fourth Year: The combination seed is planted and operation of 1st year repeated. 5 ) Fifth Year: Second year operation repeated. 6 ) Sixth Year: Third year operation repeated.

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