The Chromosomal theory Or chromosomal theory of inheritance is one that developed in the path of biologists to try to explain the transmission of phenotype and genotype of the progenitors to their offspring.
This theory states that alleles are parts of paired homologous chromosomes and was independently developed in 1902 by Theodor Boveri (Germany) and Walter Sutton (United States).
This pair of scientists, for their part, observed a relationship between the inheritance of inheritable factors and the behavior of the chromosomes during the processes of meiosis and fertilization.
Thus they deduced that the hereditary factors, called genes by Johannsen in 1909, resided in the chromosomes.
However, this approach had many detractors, until Thomas Hunt Morgan, in 1915, proved its validity and was accepted by the scientific community.
The chromosomal inheritance theory explains the free and independent heritability of one allele over another, by assuming that the different alleles are located on different chromosomes that combine in the midst of the process of maturation and fertilization, and then distribute independently one of the others.
Background and evolution of chromosome theory
Johann Gregor Mendel , in his work" Experiments on plant hybrids "Published in 1865, with which he attempted to explain the subject of heredity, postulated the law of gene segregation (Mendel's first law) and the law of independent gene transmission (Mendel's second law).
Without realizing it introduces the fundamental concepts of the genetics, unknown for its time as also were the molecule of DNA or the chromosomes.
Nevertheless, his work remains hidden or misunderstood until 1900, when Hugo de Vries (Holland), Carl Correns (Germany) and Erich Tschermak (Austria), rediscovered it.
This is due to the fact that even when they independently investigated they reached the same conclusions as Mendel: the proportions 3: 1 and 9: 3: 3: 1 for mono and dihybrid crosses, respectively, and the laws of segregation and independent transmission of genes .
At the same time, in England, William Bateson reviewed Mendel's work for the first time and disseminated it by recognizing it as an unprecedented contribution.
In fact, in Mendelian postulates he based his investigative work since 1905, according to which the transmission and appearance of certain traits, from parents to children, is due to the presence or absence of certain"factors".
His research led him to discover that such"factors"can interact with each other, and give rise to different and new characters (proportions 9: 4: 3 and 9: 7 of dihybrid crosses).
In this way, Bateson treated the exceptions that were discovered and that rivaled the proposal of Mendel. He called these exceptions"coupling"and"repulsion"of factors.
It was these"exceptions"that also interested Thomas Hunt Morgan and his disciples (the Drosophila group) who began their work in 1910.
In their inquiries, they observed three pairs of homologous chromosomes (autosomes) in males of the vinegar fly species, along with a pair of similar chromosomes, which were not identical, which they called heterochromosomes and identified with the letters X and Y.
Later, Morgan discovered that various features such as the color of the fly's body, the color of its eyes, the size of its wings, etc., were inherited and transmitted together.
After several tests concluded that there were four groups of genes that were inherited linked, because they were on the same chromosome. For this reason he called them linked genes.
Morgan continued his research and determined that the genes are located linearly on the chromosomes.
He also determined that the exchange of chromosome fragments responds to recombination, and that genetic information conserves and transmits these chromosomes through the process of mitosis.
All this meant that the chromosomes are distributed along with the factors it contains, during the processes of reduction and reproduction. These are: coupled, not independent.
It was thus, thanks to the work of Morgan and his"Drosophila group"(Alfred Henry Sturtevant, Calvin Blackman Bridges and Hermann Joseph Muller), that the chromosomal theory of heredity was finalized.
Importance of chromosome theory
It should be noted that these seem obvious today, but as with all the great discoveries of science it took all these experiments and antecedents to reach the genetics that is known today.
For example, at that time it was not known that genes are specific portions of DNA inserted in the chromosomes, which was known at the beginning of years 50 and only after surpassing the findings of the genetics of populations and on the physical nature of the Genes.
In fact, those early works on the physical mapping of genes were performed at the cellular level.
It was Alfred Sturtevant who made the first genetic map of a chromosome as a graphical representation of the possible organization of the factors in it, but he recognized the limitation of the fact that the mapping was based on data from genetic crosses rather than analysis Cytological tests.
However, these maps were then built on the basis of current mapping of molecular markers.
All these works and discovery paved the way for what has become known as the DNA era, a period in which the elucidation structure of DNA was detailed (James Watson and Francis Crick, 1953), the cloning and Restriction enzymes were discovered.
The latter ended up deriving the famous Human Genome project.
In short, the chromosomal theory proves to be a step in the long road that has traveled humanity to decipher the aspects related to DNA and human genetics.
References
- Cornide, M T; (2001). Plant genetics, breeding and society. Tropical Crops, 22 () 73-82. Retrieved from redalyc.org
- Cruz-Coke M, Ricardo. (2003). Recognition of classical works in the history of genetics. Medical Journal of Chile, 131 (2), 220-224.
- Figini, Eleonora and De Micheli, Ana (2005). The teaching of genetics in the middle level and polymodal education: conceptual contents in the activities of textbooks. Retrieved from ddd.uab.cat
- Jouve, Nicolás (1996). Advances in genetics and its use in non-university education. Journal: Alambique: Didactics of Experimental Sciences, 1996 OCT; III (10). Page (s): 69-78.
- Lorenzano, Pablo. (2008). Theoretical incommensurability and empirical comparability: the case of classical genetics. Philosophical analysis, 28 (2), 239-279. Retrieved from Scielo.org.ar.