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Genetics

 

INHERITANCE

The inheritance is the acquired organic similarity of the ancestors (transmission of the characters of the ascending ones to the descendants). The genetics is the science that takes care of the study of the inheritance tries to clarify the nature of the genetic material transmitted the descendants, as the transference of this material takes place and as they are the processes that assure the material accomplishment the characters.

HISTORICAL ASPECT

From the babylonian and Syria civilizations one knew that the characters are transmitted of ancestors to descendants. After Aristotle still the mechanism was not known transmission. During centuries XVII and XVIII certain preform investigators indicate that the new being or is preformed in the egg or the gametics. Later they saw that this was not certain because when studying the gametics verified that they were masses of protoplasma uniforms, others indicated that there were external mystical forces that caused the development of the egg. From the average age to century XIX the inheritance was studied by breeders of animals indicating that of the union of two ancestors they appeared descending with intermediate characteristics to the ancestors and they called hybrids, its followers were known like hybridists. Kolrenter studied the characteristics of the hybrids comparing them with the ancestors found that: the hybrids not always were of intermediate characteristics, that determined characteristics disappeared in hybrids but they appeared in his descendants.

MENDEL

Father of the genetics, discovered the basic mechanisms of the inheritance, studied the plant of the pea through different processes:

a) Selection of a variety of pure line for each character: Red x Red : 100% red

b) I cross plants that were different in a character being pure lines, Smooth x Rough : 100% smooth one; these could as well be crossed giving Smooth x Smooth : 25 % rough and 75 % smooth.

c) I cross lines of plants that were different in two characters, tall-Rojas X Small-White: 100% red and tall; when crossing itself between tall-red x tall - Red: red tall, high white, small red, small white. In order to explain this it defined the hereditary units that appear by pairs and each one will be the person in charge of a character.

Laws of the inheritance

Law of the segregation; the hereditary units exist by pairs in the individual during the formation of the gametics these separate and each one will go to a gametic, of this form each single gametic has a unit of each type.

Law of the combination; the distribution of each pair of the hereditary units is independent of the distribution of other pairs.

Terms

Parenteral generation, is the first generation. F1; first filial generation. F2; second filial generation. Phenotype, physical appearance that is from the activity of a pair of genes. Both genes that control a characteristic represent by a pair of letters, one is dominant which masks the action of the recesiv. Genotype, set of all the genes of an alive being. Individual homozygote, the one that both has genes that determine. Individual character heterozygote, the one that both has genes that determine a different character alleles, genes that are in opposition monohybrid crossover, crossover in which is present solely a pair of allele dihibrid crossover, crossover in which are present two pairs of alleles

Cytological base of the inheritance

The hereditary units must have relation with the chromosomes, after Mendel was discovered the conduct of the chromosomes during the gametogenesis. The chromosomic theory arises from the propose inheritance by Sutton (1902), the genes are in the chromosomes and they are transmitted to the descendants during the gametogenesis.

Cytoplasmic inheritance

Most of hereditary factors depends on the genes which are in the chromosomes. In many cells units exist that reproduce in the cytoplasm and they are in him transmitting itself of generation in generation, to these units is called plasmogenes, plasmones to them or plásmidos. During the mithosis the plasmids ones are divided in halves and each part goes to a certain cell, all do not have the same information but she is practically identical. How it is the prediction of results in the genetic crossovers? Examined the data we can predict the results. The possible genotypes are based on the combinations that are possible with the types of gametics. Punnett I devise the diagram or chessboard of Punnett. These are the awaited data but that they do not have to agree with the observed ones, speech of probabilities. Action of the genes. It is accepted that each gene exerts a specific action and any change in its structure is going to produce consequences at level of alteration in the activity of the lost gene and of the activity of the gene.

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