GENETICS

Abstract

Genetics is the science of heredity. Its applications invade our daily lives. Whether it is prenatal diagnosis, agronomy, biology or forensic science, the precision of genetic methods is appreciated. It is both a science, a scientific theory of biological heredity, and an investigative tool exportable to all fields of biology, in order to undertake the analysis of the most varied phenomena. Genetics studies the transmission of traits from one generation to the next as well as the passage of genes to traits. The discoveries of sexuality, Mendel's laws, the modalities of fertilization and the formation of gametes, the notions of gene, genotype and phenotype are also important for the history of genetics in all its dimensions. One of the most fascinating properties of life is that it reproduces itself every generation from single cells such as zygotes (fertilized eggs). This regeneration has existed since the origin of life and all organisms currently living on Earth, from the smallest such as bacteria to the largest such as whales, result from millions of regeneration cycles. The history of genetics begins with the discovery of sexuality and reproduction. In animals and humans, this discovery is very old, and dates back beyond Antiquity, while in plants it is much more recent, with its discovery at the end of the 17th century by "Rudolf Jakob Camerarius" and its general recognition during the 18th century. At that time, in plants as in animals, the notions of heredity, fertilization and embryo development were confused in the notion of generation, in the sense of reproduction of individuals. Naturalists, even philosophers, sought to explain the ability of living organisms to reproduce by giving descendants who, overall, resemble them. They were interested at the same time, in a non-distinct way, in reproduction, in the formation of the embryo in animals and in the transmission of characters, but with more interest in the first two points. To witness the emergence of a science of heredity, seen as the study of resemblances between parents and their children, it was necessary to wait until a separation was conceived between reproduction, the development of the embryo and the transmission of characters from generation to generation; this could only really be achieved after the work of "Gregor Mendel" who published in 1865 the result of his experiments on the crosses of strains of peas showing variations transmitted from one generation to the next. Mendel not only provided the experimental results of controlled crosses, but he also deduced the existence of discrete "factors" that transmit developmental information from a parent to its offspring. In 1900, the Dutch botanist "Hugo De Vries" rediscovered the laws established by Mendel and published in a text entitled ''on the law of segregation of hybrids'', considered as the birth certificate of genetics even if this name was not given to the new discipline until a few years later. In the same year, almost simultaneously, Carl Correns and Erich "Von Tschermak" obtained the same results as "De Vries". It was then extended to animals by "Lucien Cuenot and William Bateson". At the beginning of the 20th century, it became evident that the information specifying the development of organisms was contained in the chromosomes of the cell nucleus. The accumulation of information elements, begun in the 1920s, led to the conclusion that DNA is the genetic material.