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Genetic Terms

Just started to read Genetics? First, go through these terms.


1. Factors:- Unit of heredity which is responsible for inheritance and appearance of characters. These factors were referred to as genes by Johannsen(1909). Mendel used the term "element" or "factor".Morgan first used symbol to represent the factor. Dominant factors are represented by capital letters while recessive factor by small letters.

2 Allele:- Alternative forms of a gene that are located in the same position [loci] on the homologous chromosome is called Allele. The term allele was coined by Bateson.

3. Homozygous:- A zygote is formed by the fusion of two gametes having identical factors is called a homozygote and the organism developed from this zygote is called homozygous. Eg. TT, RR, tt

4. Heterozygous:- A zygote is formed by the fusion of two different types of gamete carrying different factors is called heterozygote (Tt, Rr) and an individual developed from such zygote is called heterozygous. The term homozygous and heterozygous were coined by Bateson.

5. Hemizygous:- If an individual contains only one gene of a pair then the individual is said to be Hemizygous. The male individual is always Hemizygous for a sex-linked gene.

6. Phenotype:- It is the external and morphological appearance of an organism for a particular character.

7. Genotype:- The genetic constitution or genetic make-up of an organism for a particular character.

Genotype & phenotype terms were coined by Johannsen.

8. Phenocopy:- If different genotypes are placed in different environmental conditions then they produce the same phenotype. Then these are said to be Phenocopy.

9. Hybrid vigour/Heterosis - Superiority of offspring over its parents is called Hybrid vigour & it develops due to Heterozygosity. Hybrid vigour can be maintained for a long time in vegetatively propagated crops. Hybrid vigour can be lost by inbreeding (selfing) because inbreeding induces Homozygosity in offspring.

Loss of Hybrid vigour due to inbreeding is called inbreeding depression.

10 Cistron

It is the functional unit of DNA consisting of several nucleotides that is capable of synthesizing a polypeptide chain

11 Recon

It is the smallest unit of DNA that would undergo crossing over and recombination

12 Mutant

It is the smallest unit of DNA that could undergo mutation

13 Mutation

Sudden drastic changes in hereditary that stay in heredity as disorders are called a mutation.

14 Trait

Genotypic characters transferred by the parent to offspring is called a trait.

15 Hybrid

Organism formed by the crossing of the gamete of contrasting character is called hybrid and the phenomenon is called hybridization.

Hybrid is formed by inbreeding cross (cross made between the gamut of the closely related organism).

16 Cybrid

Cybrid is formed by the outbreeding that is made after crossing between the gamut of a far related organism.

17 Back Cross

The Cross between the F1 generation and parental generation is called the back cross.

18 Test Cross

A test cross is a cross made between the F1 generation and recessive parent. It is often done to know if the offspring is homozygous or not or to obtain a homozygous individual.

19 Out Cross

Outcross is the cross made between the F1 generation and the dominant parent.