1.Gene. -
A gene may be defined as the unit of inheritance which is carried from the parent by a gamete in a chromosome and expression of a character in the young one in cooperation with its allele, other gene and environment. Chemically, a gene is a linear segment of DNA.
2.Allelomorphs( Allele) -
A pair of genes that control the two alternative expressions of the same character and have the same loci(sites) in the homologous chromosomes are called allelomorphs or Allele. The term allele used for any two genes of a single character.
Example - The gene T and t for tallness and dwarfness for height of pea plant. Now TT, Tt, tt are considered as allele.
3.Gene locus -
A specific region of a chromosome representing a single gene or allele is known as gene locus. The allelic genes occupy the corresponding loci in a pair of homologous chromosomes.
4.Dominant and Recessive Allele -
When two alleles representing the alternative of a character come together in an individual, usually one allele is expressed fully and the other is not at all. The overpowering of one allele by another is called law of Dominance.
The allele which always expresses itself even in the presence of its contrasting allele is known as the dominant Allele.
On the another hand, the allele which fails to express itself in the presence of its contrasting dominant Allele is called recessive allele.
Example - a guinea pig with allele Bb for coat colour is black. The B allele for black colour coat being dominant express itself and the b for white coat colour being recessive, does not express itself.
Wild and Mutant alleles-
An original allele, dominant in expression and wild spread in the population, is called wild allele.
An allele formed by a mutation in the wild allele, recessive in expression and less common in the population is termed as mutant alleles.
Homozygous organism -
An organism in which both the alleles of a character at the corresponding loci in homologous chromosomes are identical is said to be homozygous or genetically pure organism. Homozygous individuals breed true for the specific trait i.e produce offspring with similar genotype and phenotype on inbreeding. They are called pure individual.
Example - The pea plant with TT and tt allele pair are homozygous for height. The combination Of TT allele is homozygous dominant; and the combination of tt allele is homozygous recessive.
5.Heterozygous organism -
An organism in which the two allele of a character at the corresponding loci in the homologous chromosomes are unlike is said to be heterozygous for their character. Heterozygous individual do not breed true and are said to be hybrid for their character.
Example - The pea plant with Tt allele pair is heterozygous for height ia heterozygote, one allele codes for dominant trait and the other is recessive trait, and usually the dominant allele is expressed and the recessive allele remains latent.
So, the homozygous and heterozygous individual are called homozygote and heterozygote respectively.
6.F1 generation -
It is the first filial generation of hybrid offspring produced in a genetic cross between two genetically different but pure parents.
Example -
F1 generation produced by crossing TT and tt parent Pea Plants consists of Tt individuals.
7.F2 generation -
It is the second filial generation of young ones produced in a genetic cross between two F1 organisms.
8.Pure Lines -
A race of genetically pure,true breeding organisms resulting from continued selfing or inbreeding is called a pure Lines. In nature, pure Lines do not produce vigorous offspring because defective alleles may come to exist in homozygous state.
9.Genotype -
It is the sum total of genes inherited from both parents irrespective of whether they are expressed or not.
Example - TT, Tt and tt are genotype for the size of stem in pure tall, dwarf and hybrid tall garden pea.
10.Phenotype -
It refers to the expressed or observable structural and functional trait produced by the interaction of genes and environment.
Example - Tallness in pea plant, colour blindness in man are phenotype.both are noticed by eyes.
Individual of the same genotype have the same phenotype and breed alike. Individuals of different genotype may also have the same phenotype e.g the genotype TT and Tt give rise to tall pea plant.
11.Genome -
A complete set of gene (DNA instructions) contained in the haploid dose of chromosomes and inherited as a unit from one parent is known as genome. A haploid cell contains two genomes, one parental, other maternal. A cell may have more than two genomes also. Such cells are called polyploids.
12.Gene pool-
All the genotype of all the individuals in an inbreeding population make up a gene pool.