Definitions related to Biometrical Techniques in Plant Breeding

• Adaptation. The fitness of a genotype or population in a given environment or the process of adjustment of organisms to the changes occurring in the environment.
• Adaptability. The capacity of a genotype for genetic change in adaptation or capacity of a genotype or population to give stable performance over a wide range of environment.
• Additive × Additive Epistasis. Interaction between two or more loci each exhibiting lack of dominance individually. It is denoted as AA and is fixable.
• Additive × Dominance Epistasis. Interaction between two or more loci, one exhibiting lack of dominance and the other dominance. It is denoted as AD and is nonfixable.
• Additive Gene Action. Additive variance plus additive × additive type of epistasis.
• Additive variance. Average effect of alleles on all segregating loci. It results when there is lack of dominance.
• Analysis of covariance. A statistical procedure that splits the covariation of two variables into different components.
• Analysis of variance. A statistical procedure that splits the total variation into different components.
• Arithmetic mean. The sum of all the observations of a sample divided by their number.
• Average heterosis. Superiority of a hybrid over the mean values of its parents.
• B₁ and B₂. Back cross of F₁ with P₁ (first parent) and P₂ (second parent), respectively of a hybrid.
• Biometrics. The science which deals with the application of statistical concepts and procedures to the study of biological problems; also called biometry.
• Biometrical Genetics. A branch of genetics which utilizes statistical concepts and procedures for the study of genetical principles. Since biometrical genetics utilizes various statistical concepts and procedures, it is also referred to as statistical genetics or mathematical genetics.
• Biometrical technique. Various statistical procedures employed in biometrical genetics.
• Biparental Cross. Crossing of randomly selected plants in the F₂ or subsequent generation in a definite fashion.
• Bit. A binary digit, 0 and 1.
• Byte. A group of eight bits.
• Bus. A group of lines used to transfer bits between the microprocessor and the components of computer system.
• Coadaptation. A selection for a balanced combination of genes in an individual or population.
• Coefficient of determination. The square of multiple correlation coefficient.
• Coefficient of variation. The ratio of standard deviation of a sample to its mean expressed in percentage. It is a measure of variability.
• Coheritability. The ratio of genotypic covariance to the phenotypic covariance expressed in percentage. It is a measure of simultaneous inheritance of two characters.
• Computer. An electronic device that can transmit, store and process information or data. Computers are of four types: super, large, mini and microcomputers.
• Correlation. The ratio of appropriate covariance to the product of two standard deviations, i.e. Cov. xy/SDx. SDx. It is the statistics which measures the degree and direction of association between two or more variables, it is represented by r.
• Combining ability. The ability of a genotype to transmit superior performance to its crosses.
• D₂ Statistics. A biometrical technique used for the study of genetic divergence in a population.
• Diallel Cross. Mating of selected parents in all possible combinations, i.e. n(n–1)/2.
• Diallel Analysis. Analysis of a set of diallel crosses.
• Dominance Hypothesis. Heterosis due to superiority of dominant alleles over recessive alleles. Heterosis is directly proportional to the number of dominant genes contributed by each parent.
• Dominance × Dominance Epistasis. Interaction of two or more loci, each exhibiting dominance individually. It is represented as DD and is nonfixable.
• Direct Effect. In path analysis, the straight way effect of an independent character on dependent character.
• Discriminant function. A statistical approach used in the construction of selection index.
• Dominance. Masking effect of one allele over the other on the same locus.
• Dominance variance. Deviation from the additive scheme resulting from intra allelic interaction, i.e., alleles of the same locus.
• Economic heterosis. Heterosis over the commercial cultivar.
• Environment. External conditions that influence expression of genes of a genotype or individual.
• Environmental index. Mean performance of genotypes in each environment.
• Environmental Path. Path coefficients that are worked from all possible environmental correlation coefficients among various characters included in the study.
• Epistasis. Interaction between alleles of two or more different loci.
• Epistatic Variance. Deviation from the mean value as a consequence of non-allelic interaction i.e., interaction between two or more genes. It is of three types, viz., additive × additive, additive × dominance and dominance × dominance.
• F₁. The progeny obtained by crossing two different genotypes. The first generation from a cross.
• F₂. The progeny obtained by selfing or intermating of F₁ population of a cross.
• F₃. The selfed progeny of F₂ plants.
• F. Test. A test of significance that is used to compare the difference among several means.
• Five Parameter Model. A model of generation mean analysis which is based on five populations, viz., P₁, P₂, F₁, F₂ and F₃ generations of a cross. It provides information about five parameters, viz., m, d, h, i and l.
• Fixable Gene Action. Type of gene action that can be fixed as a true breeding line. It includes additive gene action and additive × additive type of epistasis.
• Floopy disk. A thin plastic disk coated with magnetic oxide and used for information storage.
• Full Diallel. All possible both way direct and reciprocal crosses among n genotypes.
• Full sib. Progeny of the mating of two individuals.
• Gene action. The mode of expression of genes in various characters of a population.
• Gene interaction. Modification of gene action by non-allelic genes.
• General combining ability. Average performance of a strain in a series of cross combinations.
• Generation mean analysis. The biometrical analysis which is based on the mean values of six populations, viz., P₁, P₂, F₁, F₂, B₁, and B₂.
• Genetic advance. The improvement in mean genotypic value of selected plants over the parental population.
• Genetic diversity. Variability between different genotypes of a species.
• Genetic homeostasis. The genetic buffering capacity of a genotype to environmental fluctuations.
• Genetic Polymorphism. The regular occurrence of several phenotypes in a genetic population due to superiority of heterozygote over homozygotes; also called balanced polymorphism.
• Genetic Variance. Heritable portion of total or phenotypic variance. It is of three types, viz., additive, dominance and epistatic variances.
• Genotypic correlation. The inherent association between two variables.
• Genotypic Path. Path coefficients that are worked out from all possible genotypic correlation coefficients among various characters included in the study.
• Half Diallel. All possible one way (direct) crosses among n genotypes.
• Half sibs. Progeny having one parent in common.
• Heritability. The ratio of genotypic variance to total or phenotypic variance (broad sense) and the ratio of additive genetic variance to phenotypic variance (narrow sense).
• Heterobeltiosis. The superiority of a hybrid over its better parent.
• Heterosis. The superiority of a hybrid for one or more characters over its parents.
• Heterozygote. An individual having unlike (dissimilar) alleles on the corresponding locus of homozygous chromosomes.
• Heterozygosity. The proportion of heterozygous individuals in a population.
• Homeostasis. The buffering capacity of a genotype to environmental changes.
• Homozygote. An individual having like (similar) alleles on the corresponding locus of homozygous chromosomes.
• Homozygosity. The proportion of homozygous individuals in a population.
• Hybrid. The progeny of a cross between genetically dissimilar parents.
• Hybrid Variety. The F₁ population that is used for commercial cultivation.
• Inbred. In cross pollinated species, a true breeding line obtained by continuous inbreeding.
• Inbreeding. Mating between closely related individuals. The self pollination is the common form of inbreeding.
• Inbreeding depression. Reduction in vigour, reproductive capacity (fitness) and productivity due to fixation of unfavourable recessive genes in F₂ as a result of inbreeding.
• Indirect Effects. In path analysis, the effects of an independent character on the dependent one via other independent characters.
• Line × Tester analysis. A modified form of top cross used for measuring general combining ability and specific combining ability variances and effects in large number of germplasm lines at a time.
• Luxuriance. Superiority of F₁ over its parents in vegetative growth, but not in yield and adaptation; also called pseudoheterosis.
• Macro-environment. Environmental differences that are easily detectable such as effect of fertilizer doses, planting dates, spacings, irrigation schedules etc.
• Metroglyph analysis. A semigraphic method used for the assessment of morphological variation in the gene pool.
• Mid-Parent Heterosis. Heterosis over the mean value of both the parents; also called mean heterosis.
• Microcomputer. A computer that is designed using a microprocessor as its central processing unit (CPU). It includes four components: microprocessor, memory, input and output.
• Micro-environment. The environment of a single genotype or population as opposed to another genotype growing at the same time in almost the same place.
• Microprocessor. A semiconductor device manufactured by using the large scale integration technique. It includes arithmetic logic unit (ALU), register arrays and control circuit on a single chip.
• Multiple correlation. Joint influence of two or more independent variables on a dependent variable. It is denoted by R.
• Nibble. A group of four bits.
• NCD 1. A design of biparental cross in which in F₂ each male is mated to a different group of females resulting in f crosses, where f is the number of female plants used for crossing in a set.
• NCD 2. A design of biparental cross in which in F₂ each selected male is mated to the same set of female plants resulting in mf crosses, where m and f denote number of male and female plants.
• NCD 3. A design of biparental cross in which in F₂ each randomly selected male plant is mated to P₁ and P₂ parents of original cross resulting in 2m crosses, where m is the number of male plants used per set.
• Non-additive Gene Action. Joint effects of dominance and additive × dominance and dominance × dominance epistasis.
• Nonfixable Gene Action. Type of gene action that can not be fixed as a true breeding line. It includes dominance gene action and additive × dominance and dominance × dominance types of epistatic gene actions.
• Outbreeding. Mating between unrelated individuals. The cross pollination is the common form of outbreeding.
• Overdominance. The superiority of heterozygote (Aa) over both the homozygotes (AA and aa).
• Overdominance Hypothesis. Heterosis due to superiority of heterozygote over both the homozygotes.
• P₁ and P₂ The first and second parent of a cross, respectively.
• Partial correlation. The correlation between two variables eliminating the effect of third variable. It is denoted as r₁₂.₃
• Partial diallel. The number of sampled crosses per parent or per array in all possible combinations of a given set of parents.
• Path analysis. A standardized partial regression coefficient which splits the correlation coefficient into the measures of direct and indirect effects and measures the direct and indirect contribution of each independent variable on the dependent variable.
• Path Diagram. A line diagram which is constructed in path analysis to depict the cause and effect situation.
• Phenotypic correlation. The observable correlation between two variables.
• Phenotypic Path. Path coefficients that are worked out from all possible phenotypic correlation coefficients among various characters included in the study.
• Phenotypic variation. The total or observable variation in a population. It consists of genotypic and environmental components.
• Physiological homeostasis. The physiological buffering capacity of a genotype to environmental changes.
• Polygenic inheritance. The inheritance of quantitative character.
• Program. A set of instructions written in a specific sequence for the computer to accomplish a given task.
• Quadriallel analysis. The analysis of double cross hybrids.
• Qualitative trait. A character showing discontinuous variation and governed by oligogenes.
• Quantitative genetics. A branch of genetics which deals with the inheritance of quantitative or polygenic characters.
• Quantitative trait. A character showing continuous variation and governed by polygenes.
• Range. The difference between the lowest and the highest value of observations in a sample. It is a measure of variability.
• Regression coefficient A measure of change in the dependent variable with unit change in independent variable.
• Residual Effect. In path analysis, the measure of the effect of other possible independent variables, which were not included in the study, on the dependent variable.
• ROM. (Read Only Memory) A memory that stores binary information permanently. The information can be read from this memory but can not be altered.
• R/WR. (Read/Write Memory) A memory that stores binary information during the operation of computer. This memory is used as writing pad to write user programs and data. The information stored in this memory can be read and altered easily.
• Selection differential. The difference between mean genotypic value of the progeny of selected plants and parental population. It is denoted by K.
• Selection parameters. The biometrical estimates which aid in the selection of elite genotypes from a diverse or segregating population.
• Shuttle breeding. A breeding programme in which seed shuttles between two or more locations for varietal testing to develop cultivation with broad adaptation.
• Simple correlation. The association between two variables.
• Six Parameter Model. A model of generation mean analysis which provides information about six parameters, viz., m, d, h, i, j and l.
• Specific combining ability. The deviation of a particular cross from the general combining ability.
• Stability. The suitability of a variety for general cultivation over a wide range of environmental conditions.
• Standard deviation. The sum of square of deviations of all observations of a sample from its mean, divided by degrees of freedom and taking the square root or it is the square root of variance and is the measure of variation.
• Standard error. A measure of uncontrolled variation in a sample. It is estimated by dividing the standard deviation by the square root of the number of observations in a sample.
• Standard heterosis. The superiority of a hybrid over the local commercial hybrid of a crop.
• Statistics. A science which deals with the collection, presentation, analysis and interpretation of numerical data.
• Test of significance. Statistical procedure that is used to decide whether the differences under study are significant or non-significant. It includes z test, t test and F test.
• Tester. A common parent used in crossing with several lines.
• Three Parameter Model. A model of generation mean analysis which provides information about three parameters, viz., m, d and h.
• t-Test. A test of significance that is used for comparing two means when sample size is small (30 and less). It is of two types, Student’s t-used with paired observations, and Fisher’s t-used when observations are not paired.
• Top Crosses. Various crosses made using a common tester; also known as test crosses.
• Triallel analysis. The analysis of a three way cross or a cross involving three parents.
• Triple test cross. Crossing of randomly selected F₂ plants with both the parents (P₁, P₂) involved in the cross, and with their F₁ hybrid.
• Useful heterosis. The superiority of a hybrid over the commercial variety of a particular region.