Page 1 :
GENETIC VARIANCES AND GENE ACTION, , ., rac on » 1c AA CLITeEC 4, A, Measureme nt. It is measured by various biometrical techni 1, combining ability [sca] is a measure of dominance varian (ta cae, ce., , , , sy a Saloget ne 7 ; 4, 5. Effect of Se lection. Dominance variance is non-fixable and ,therefore, selecti, traits governed by dominance variance is not effective. a, , 6. Uses. Dominance variance is the chief cause of heterosis or hybrid vigou, “ ~' edi i , :, 7, Effect of Inbreeding. Dominance variance gets depleted though selfing or inbreeding, , EPISTATIC VARIANCE __, , The deviation from the additive scheme of gene action which results due to inter-allelic, interaction Is called epistatic variance, The main points related to additive genetic variance, are presented as follows., , , , , , os Expression. Epistatic__genes interact and sometimes lead to new , phenotypic, expression. The genes may be dominant or recessive. ee, , a. Magnitude. In natural plant breeding population, epistatic genetic variance has the, , lowest magnitude. 4, , 3. Components. Epistatic variance includes both additive and non-additive components., , 4. Types. Epistatic variance is of three types, viz., additive x additive, additive =, dominance and dominance x dominance., , ee, , , , , , Comparison of Genetic Variances, There are several differences among additive, dominance and epistatic variances. These, are presented below [Table 7.1)., , TABLE 7.1. Differenc, , Particulars | Don ance Variance —, A | Expression Incomplete, complete or overdominance, Moderate, , , , , , , s between Additive and Dominance variances., , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Intermediate, , , , , , , , , , , , , , , , , , , , Magnitude in natural Highest, , populations, , , , , , , , , , , , , Biometrical techniques, Heterozygosity, Non-effective, , Heterosis breeding, Not possible, , Negative, , Non-fixable, , Cross pollinated species, , Biometrical techniques, Homozygosity, , Effective, , Pure line & Mass selection, Possible, , Positive, , Fixable, , Self pollinated species, , (i Additive * additive epistasis yefers to interaction between two ormore loci each, exhibiting lack of dominance ‘individually. It is denoted as AA and is fixable. It, ion., , comes under additiv, , Measurement by, Associated with, Selection, , Used for, , Transgressive segregation, Effect of inbreeding, Fixable or non-fixable, More in