genotype

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genotype

(jēn`ətīp'): see geneticsgenetics,
scientific study of the mechanism of heredity. While Gregor Mendel first presented his findings on the statistical laws governing the transmission of certain traits from generation to generation in 1856, it was not until the discovery and detailed study of the
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.

genotype (and phenotype)

the unique collection of genes an individual receives from both parents as a result of cell division (meiosis) and fusion of the ovum and sperm (fertilization). All these genes have the potential to determine, or help determine, characteristics of the individual, but not all will in fact exert an influence since they are received from both parents and the gene for a characteristic, e.g. eye colour, from one parent may be dominant over that from the other parent. The genotype therefore expresses genetic potential, and even though genes may not be expressed in the individual they will be passed on to the offspring.

While the genotype is the total genetic potential of the individual, the phenotype is the actual expression of the genes as the individual. The phenotype therefore describes the pattern of genes that have influenced the development of the individual, e.g. the gene for the individual's eye colour, but not for the eye colour not exhibited, though still carried in the genotype.

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

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.
References in periodicals archive ?
The contribution of social effects to heritable variation in finishing traits of domestic pigs (Sus scrofa).
Gametophytic selection in Raphanus raphanistrum: a test for heritable variation in pollen competitive ability.
45% A July paper suggested that common variants may explain as much as 45 percent of heritable variation in height.
Heritable variation in stomatal responses to elevated [CO.sub.2] in wild radish, Raphunus raphanistrum (Brassicaceae) Am.
These estimates provide information on whether narrow-sense heritabilities computed in laboratory environments can be related to heritable variation in the field.
It is clear that heritable variation (usually maternal genotype), maternal environment, and germination environment can all contribute to variable germination behavior.
Natural selection acts on this heritable variation among a population to adapt it to changing environmental conditions.
Maynard Smith (1978, 1985) argued that heritable variation of the preferred male traits would decrease as these traits became fixed leaving no genetic advantages for the choosy females compared to those mating at random.
Several suggestions have been made as to how heritable variation in egg size can persist in the population in spite of selection.
However, values of "explained" heritable variation (VQTL) were generally higher in the MN than in the MA or NA populations.
The extent of heritable variation of a polygenic trait determines its immediate evolutionary response to selection (Falconer 1989).
Heritable variation was calculated by two-way ANOVA where one factor was the RI genotype and the other was the environment (SAS, 1988).