GENETICS; HISTORY !!

 INTRODUCTION TO GENETICS

VARIOUS DEFINITIONS OF GENETICS;

·         Genetics is PRIMARILY and ORIGINALLY a science dealing with heredity, Heredity itself being the transfer of characteristics from parents to offspring. In addition, it also involves the study of the factors which show the relationship between the parent and the offspring and also which account for the characteristics which an organism posseses

·         Genetics is a science which tries to account for variations and similarities between related individuals

·         Genetics is a scientific study of the BIOLOGICAL COMMUNICATION between GENERATIONS using the HEREDITARY FACTORS i.e The science studies the transmission of hereditary factors from parents to offspring

·         Genetics is a science DEALING with heredity and variation and SEEKING to discover laws governing the similarities and differences in INDIVIDUALS related to a descent.BATSEN IN 1906

·         The factors (hereditary factors) are called genes—Johannsen in 1909

CONTRIBUTIONS IN THE WORK OF EVOLUTION

·         HIPPOCRATES; Around 400 BC brought about the theory of the existence of representative elements of all parts of a parent concealed in a semen and that these parts were what directed the development of the embryo. This theory believed that acquired traits of the parents can be transferred to offsprings

·         ARISTOTLE; 384-322 BCE he later disproved the theory postulated by Hippocrates noting the fact that not all crippled or maimed parents produced deformed offspring. He postulated that the fathers semen had the FORM, while the mother’s blood had the SUBSTANCES. The father’s semen had the plan to which the mother’s armophous blood must be conform. Aristotle noticed that this transmission was not just of parts but information that guided the embryonic development and called it a ‘MYSTICAL INFLUENCE’ since it could not be seen. This was later called the ‘AURA SEMINALIS’ by HARVEY

·         JAN SWAMMERDAM; He postulated the ‘PREFORMATION THEORY’ in the 17^th and 18^th century when the sperm and egg cells were discovered. This theory believed that either the sperm or the egg contained the whole organism in a miniaturized but perfect form. For the male, the sperm was belived to contain a miniature human being called HOMUNCULUS. This theory was disproved because it implied that even in the miniature structure is embedded another and another inside the other infinitely

·         CHRISTIAN WOLFF; He disproved the preformation theory in the 18^th  after noticing in plants and animals that the adults developed from embryonic tissues which looked nothing like the adults, he then belived that a vital force was responsible for what he considered a de novo origin of the adults (THEORY OF EPIGENESIS). KARL ERNST VON BAER in the 19^th century modified this theory by stating that the adult emerged from embryonic tissues that had undergone or were undergoing gradual transformation and differentiation. The epigenetic theory was basically correct, but did not state the form in which the transformed materials ( embryonic tissues) existed.

·         PIERRE-LOUIS MAUPERTUIS; In the early 19^th century she postulated that during sexual reproduction, different parts contributed particles that came into fusion from each parents i.e from the male and from the female but in certain cases the male particles may predominate leading to a male child and in other cases the female particles may predominate leading to a female child. This theory took into considerations the contributions from each party involved in the sexual reproduction, but by suggesting that the body parts contributed particles it lead back to the theory of evolution by JEAN-BAPTISTE LAMARCK which basically implied that acquired traits by parents could be transferred to offspring which was later formalized by CHARLES DARWIN in ‘the provisional hypothesis of pangenesis’ stating that exact miniature replicas(gemmules) of the body parts were present in the blood stream and are to be assembled in the gametes. In the zygote, there is appropriate organizing of these body parts and implying that the parents acquired structures or traits are transferred since the gemmules are body parts. The theory of pangenesis was later disproved by AUGUST WEISMANN who carried out experiments cutting the tails  of mice for 22 generations and yet they still produced normal tail length offsprings

·         MENDEL; He carried various experiments using the pea plant and thereby came up with many profound truths about inheritance and are now the basic foundation in genetics