Genes and Genetic

Genetic Terminology  

• Character: It is a specific feature of an organism e.g. height of stem (plant). 

• Trait: An inherited character and its detectable variant e.g. Tall or dwarf 

• Factor: It is a unit of heredity, a particle present in the organism which is responsible for the inheritance and expression of a character. (factor is passed from one generation to the next through gametes). 

• Gene: It is a particular segment of DNA responsible for the inheritance and expression of that character. 

• Alleles or Allelomorphs: The two or more alternative forms of a given gene (factor) are called alleles of each other. 

• Dominant: It is an allele that expresses its trait even in the presence of an alternative allele i.e. in heterozygous condition only. Alternatively, the allele that expresses in F1 is called dominant. 

•  Recessive: This allele is not expressed in the presence of an alternative allele (in heterozygous condition). It expresses only in the presence of another identical allele. It is an allele that does not express in F1 hybrid. 

• Phenotype: The external appearance of an individual for any trait is called phenotype for that trait. 

• Genotype: Genetic constitution or genetic make up of an organism with respect to a particular trait.  

• Homozygous (pure): An individual possessing identical alleles for a particular trait, is called homozygous or pure for that trait. 

• Heterozygous: An individual possessing contrasting alleles for a particular trait, is called heterozygous. 

• Pure line: An individual or a group of individuals (population) which is homozygous or true breeding for one or more traits, constitutes pure line i.e. plant which breeds true for a particular character 

• Monohybrid: It is heterozygous for one trait and is produced from a cross between two pure parents differing in single pair of contrasting characters.  

• F1 generation: It refers to the first filial generation. It consists of all off-springs produced from a parental cross. 

•  F2 generation: The second generation (progeny) produced by selfing (inbreeding) of F1 generation offsprings is called second filial generation. 

• Punnett square/ Checkerboard: It is a diagrammatic representation of a particular cross to predict the progeny of a cross. 

• Homologous Chromosomes: The morphologically, genetically and structurally essentially identical chromosomes present in a diploid cell, are called homologous chromosomes. Such chromosomes synapse during meiosis. 

• Back cross: It is a cross of F1 progeny with any of the parents (e.g. F1 tall × pure tall; F1 Tall × pure dwarf i.e. Tt × TT/tt). 

• Test cross: It is a cross of F1 progeny with homozygous recessive parent (e.g. F1 tall u pure dwarf i.e. Tt × tt). 

• Phenotypic ratio: It is the ratio of the offsprings produced in F2 and subsequent generation with respect to their physical appearance. 

• Genotypic ratio: It is the ratio of the offsprings produced in the F2 and subsequent generation with respect to their genetic make up