Genotype

genotype (jēn`ətīp'): see genetics.

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genotype

Genetic makeup of an organism. The genotype determines the hereditary potentials and limitations of an individual. Among organisms that reproduce sexually, an individual's genotype comprises the entire complex of genes inherited from both parents. Sexual reproduction guarantees that each individual has a unique genotype, except for identical twins, who come from the same fertilized egg. See also phenotype, variation.

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genotype [′jē·nə‚tīp]

(genetics)

The genetic constitution of an organism, usually in respect to one gene or a few genes relevant in a particular context.

(systematics)

The type species of a genus.

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Genotype 

the sum total of all the genes localized in the chromosomes of a given organism. In a broader sense, the genotype is the sum total of all the hereditary factors of the organism, both nuclear (genome) and nonnuclear, or extrachromosomal (that is, cytoplasmic and plastid hereditary factors). The term was introduced by the Danish biologist W. Johannsen in 1909.

The genotype is the carrier of hereditary information, transmitted from generation to generation. It is the system that controls the development, structure, and vital activity of the organism, that is, the sum total of all the characteristics of the organism—its phenotype. The genotype is an integral system of interacting genes, so that the expression of each gene depends on the genotypic environment in which it is located. For example, the red coloration of the blossoms in some varieties of the sweet pea arises only during the simultaneous presence in the genotype of dominant alleles of two different genes, whereas separately each of these alleles causes a white coloration of the blossoms. The interaction of the genotype with the complex of factors of the internal and external environment of the organism cause a phenotypic manifestation of characteristics. The coloration of the fur of rabbits of the so-called Himalayan line serves as an example of the influence of the environment on phenotypic manifestation of genotype. Although they have one and the same genotype, these rabbits when raised in cold temperatures have black fur; when raised in moderate temperatures they have the Himalayan coloration (white with black noses, ears, feet, and tail). When raised in hot temperatures they have white fur. The offspring of these three groups of animals inherit not one immutable coloration of fur but, rather, the ability to produce a particular coloring depending on environmental conditions. Thus, in a general sense, it is more correct to say that the genotype determines the inheritance not of concrete traits but of the norm of reaction of the organism to all possible conditions of the environment. Some genes are in an active state at certain times in an individual’s development, while other genes may become active at other times; therefore, in ontogenesis the genotype functions as a changeable mobile system.

The term “genotype” is sometimes used in a much narrower sense to denote simply groups of genes or even individual genes whose inheritance is being studied. For example, the splitting offspring of the monohybrid cross AA x aa are commonly said to have genotypes AA, Aa, and aa, and the possible differences based on other genes between corresponding individuals (or groups of individuals) is disregarded.

V. I. IVANOV