Medical Genetics Lecture 1 PDF

MEDICAL GENETICS KNUR 221 INSTRUCTOR: OTABIL EMAIL:[email protected]  2 INTRODUCTORY GENETICS WHAT IS GENETICS? It is the branch of biology that deals with heredity and variation. The hereditary units transmitted from generation to generation (i.e. Inherit...

MEDICAL GENETICS KNUR 221 INSTRUCTOR: OTABIL EMAIL:[email protected]  2 INTRODUCTORY GENETICS WHAT IS GENETICS? It is the branch of biology that deals with heredity and variation. The hereditary units transmitted from generation to generation (i.e. Inherited) are called GENES.  Genetics is concerned with the transmission, expression, and evolution of genes (i.e. the molecules that control the function, development and the ultimate appearance of individuals). Early Ideas About Heredity The existence of biological heredity is obvious in the resemblance of children to their parents. It was long known that in humans and animals, the sexual act was involved in procreation.  5 It was therefore natural to assume that semen was the carrier of heredity, but how this was accomplished proved difficult to establish GENETICS THEORIES Pangenesis Lamarckism Pre-formation Epigenesis Charles Darwin Jean Baptiste Lamarck  6 PANGENESIS Every inherited structure will pass on its characteristics by contributing a small amount to the gonads (sex glands, reproductive glands). Particles (pangenes or gemmules) formed in each body part are transported through the blood vessels to sperms/eggs and then inherited by offspring.  7 Proposed by Charles Darwin The similarity between parents and offspring was accounted for by postulating that the pangenes or gemmules formed in each part of the body reflected the characteristics of that part. Aristotle and other ancient Greeks supported this theory. It prevailed for many centuries into the 19th Century.  8 LAMARCKISM Evolution was the result of acquired characteristics accumulated over many generations: e.g. in body modifications such as muscle development in an athlete, these characteristics could be transmitted to the offspring if the semen formed throughout the body would reflect such modifications. Another explanation was that organisms acquired traits during their life-times and then passed on those traits to their offspring.e.g. tattoo or scar would be inherited as tattoo or scar pangenes.  9 GERMPLASM THEORY The first serious challenge to the theory of pangenesis was made by August Weismann. He proposed, instead, the germplasm theory. (Read more about this theory)  10 PREFORMATION Explains the differentiation that takes place in the zygote which contains tiny amount of material into a human being. E.g., after cell proliferation, there is differentiation into arms, legs, liver, etc. with diverse shapes and functions. In the late 17th century, an observer using a primitive microscope and a lively imagination claimed to have seen a miniature figure called a homunculus of a man inside the human spermatozoon. Jan Swammerdam and Charles Bonnet discovered this theory and were supported by other scientists then.  11 Homunculus: little man in a sperm cell The human body, according to some preformationists, was already preformed in the spermatozoon. Development was simply a matter of growth of the zygote There were the “spermatists” and the “ovists”.  12 EPIGENESIS Kasper Wolff and Karl Ernst von Baer proposed this theory in the 18th and 19th centuries. This theory discredited or disproved Pangenesis, Lamarckism and Preformation. According to this theory, the sex cells are largely homogenous bits of organic matter and contain nothing resembling the body that will develop from them. Development is differentiation as well as growth. The various tissues and organs gradually form from the zygote through a series of transformations.  13 CONCLUSIONS What is transmitted from parents to offspring is a set of “instructions”, i.e., the genetic information in the DNA, which interacting with the environment, direct the development of the organism. The theory of epigenesis was more accurate than that of preformation. The organism is not preformed in the zygote.  14 RECOMMENDED TEXTBOOKS Principles of Genetics; 8th Edition (1991). Gardner, E. J.; Simmons, M. J. & Snustad D. P. Principles of Genetics; 4th Edition (1993). Tamarin, R. H. Modern Genetics; 2nd Edition (1984)Ayala, F. J. & Kiger Jr, J. A. Concepts of Genetics; (1983). Klug, W. S. & Cummings, M. R. THANK YOU