Question

Example terminologies in heredity​

Answer 1

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Gene, allele, locus, site

In the original terminology, still used by some population geneticists, genes occur in pairs on homologous chromosomes. In thisterminology the four blood groups A, B, O and AB (defined in terms of agglutination reactions) are determined by three (allelic)genes: A, B and O.

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Answer 2

$\Large{\underline{\underline{\bf{Terminologies:-}}}}$

Character: It is distinct well defined morphological or physiological feature of the individual, e.g., height.

Traits : It is a distinguishable expression of a character, e.g., tallness or dwarfness (for the character of height).

Factor: It functions as a unit of inheritance passing from generation to generation and controlling expression of a character, generally alongwith another factor of the same character. The term factor has been replaced by gene

(Johannsen, 1909). Gene is a unit of inheritance which consists of a linear segment of chromosome or DNA that takes part in expressing a particular character.

Alleles: They are various forms of a gene which occur at the same particular position over the chromosome. e.g., TT, Tt, tt.Symbols (Gene Symbols). Each gene or its character is given a symbol generally in the form of a capital letter for the dominant trait and small alphabet for the recessive trait, e.g., T— t (tallness —dwarfness), R— r (round —wrinkled), Y — y (yellow —green).

Phenotype: It is observable characteristic of an individual, e.g., tall, dwarf.

Genotype: It is a gene complement of an individual with regard to one or more characters, e.g., TT, Tt, tt. Genotype TT and Tt are different but they have the same phenotype. The monohybrid ratio of 3 : 1 is phenotypic ratio. Its genotypic ratio is 1 : 2 : 1.

Homozygous: It is an individual having identical alleles of a gene, e.g., TT, tt.

Heterozygous: An individual having both the contrasting alleles of a character is called hybrid or heterozygous individual, e.g., Tt.

Dominant factor : It is a factor or allele which can express its effect whether present in homozygous or heterozygous state, e.g., T (in TT, Tt).

Recessive Factor. The factor or allele which is unable to express its effect in the presence of contrasting factor is called recessive factor (e.g., t)

F_1 Generation: First Filial or Son and Daughter Generation is thegeneration of hybrids produced from a cross between genetically different individuals called parents.

F_2 Generation: F2 or second filial generation is the generation of individuals which develops as result of inbreeding amongst individuals of F1 generation.

Monohybrid Ratio: It is the ratio obtained in F_2 generation when a monohybrid cross is made and the offspring of F_1 generations are self-bred . Monohybrid ratio is 3 : 1 (phenotypicratio) and 1 : 2 : 1 (genotypic ratio).

Dihybrid ratio : It is ratio which is obtained in F2 generation when a dihybrid cross is made and the individual of F1 generation are self-bred. Dihybrid ratio is 9 : 3 : 3 : 1 (phenotypic) .

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