Definitions of Important Terms

Heredity :

Transmission of characters from one generation to the next generation is called heredity.

Variation :

The differences between parents and offspring or among the offspring of the same parents and among individuals of same species is called variation.

Genetics :

It is the branch of biology which deals with the study of heredity and variation. The term genetics was coined by William Bateson is 1906.

Factor :

Particle present in the organism which is responsible for the inheritance and expression of the character.

Gene :

Specific segment of DNA which determines a particular character of an organism.

Alleles or Allelomorphs :

Two or more alternative forms of a gene present at the same loci of homologous chromosomes and controlling the same character are called as alleles or allelomorphs.

Homozygous :

An individual having identical alleles for a particular character is homozygous for that character. It is pure or true breeding e.g. TT, tt.

Heterozygous :

An individual having dissimilar alleles for a particular is heterozygous for that character. It is a hybrid. e.g. Tt

Genotype :

It is the genetic constitution of an organism. e.g. TT, Tt, tt

Phenotype :

The external appearance of an organism. e.g. tallness, dwarfness.

Monohybrid cross :

A cross between two pure parents differing in single pair of contrasting character is called monohybrid cross. The ratio for this cross is 3 : 1.

Dihybrid cross :

A cross between 2 pure parents differing in two pairs of contrasting characters is called dihybrid cross. The ratio for such cross is 9 : 3 : 3 : 1.

F1 generation :

The hybrid individuals obtained by a cross between two pure parents with contrasting characters is called F1 generation or first filial generation.

F2 generation :

The generation of offspring obtained by selfing of F1 individuals is called F2 generation or second filial generation.

Dominant :

The character expressed in F1 generation is called dominant character.

Recessive :

The character which is not expressed in F1 generation is called recessive character.

Offsprings :

The individuals produced by the sexual reproduction are called offsprings.

Progeny :

All offsprings produced by the parents are called progeny.

Hybrid :

Heterozygous individual produced by parents having contrasting characters.

e.g. Tt.

Character :

A visible feature is a character e.g. height, seed colour.

Trait :

One form of the visible feature e.g. tallness or dwarfness, yellow or green.

Homologous chromosomes or Homologues :

Morphologically, physiologically and genetically similar chromosomes present in a diploid cell are called homologues or homologous chromosomes.

In each pair of homologous chromosome, one chromosome is maternal and the other is paternal.

Emasculation :

Removal of stamens well before anthesis is called emasculation. It is done in bud condition.

Dihybrid :

It is heterozygous for two traits and produced in a cross between two parents differing in two pairs of contrasting characters.