Genetics

• Genetics the study of heredity and variation.
• Genetics derived from the Greek word genesis meaning origin.
• Genetics is concerned with the transmission, expression and evolution of genes.
• Moist Vapour Theory 

  Pythagoras believed that each organ of the body male produced moist vapours during coitus which formed the body parts of the embryo.
• Fluid Theory

  Empedocles , proposed that each body part produced a fluid. The fluid of different body parts of the two parents mixes up and is used in the formation of embryo. Any defect in the descent and mixing up of the fluids results in missing of characters of one parent or both the parents
• Reproductive Blood Theory

  Aristotle thought that the males produce highly purified reproductive blood containing the nutrients from all body parts. Females also produce reproductive blood but this is impure. The two reproductive bloods coagulate in the body of the female and form the embryo. Due to purity of reproductive blood, the contri-bution of characters by the male is more than the female. 
• Preformation Theory

  The theory of preformation believes that the organism is already present, i.e., preformed in the sperm or egg in a miniature form called homunculus. 
• Homonculus fertilization is required to stimulate its growth. 
• Sperms were observed for the first time by Leeuwenhoek, in 1672.
• Preformation theory was given by Swammerdam (1679) and advocated by Malpighi (1673). 
• Theory of Acquired Characters

  Proposed by the famous French biologist Lamarck (1744-1829) this theory states that a new character once acquired by an individual shall pass on to its progeny.
• Acquired Theory It means if a man develops a strong muscle by exercise, all his children would have strong muscles. On the other hand, if a person becomes weak all his children would be weak.
• This concept was totally rejected by Weismann on the basis of experiment on rats performed through 22 generations.
• Theory of Epigenesis

  Proposed by a German biologist Wolff (1738-1794), the theory states that the egg and sperms are undifferentiated cells. 
• Theory of epigenesis the differentiation into various organs/parts takes place only after fertilization in the zygote resulting in the development of adult tissues and organs. This concept is universally accepted
• Blending theory

  The mixture of sperm and egg resulted in progeny that were a “blend” of two parent’s characteristics.
• The mixture of sperm and egg resulted in progeny that were a "blend" of two parents' characteristics. Sex cells are known collectively as gametes (gamos, Greek, meaning marriage). 
• Blending inheritance was discarded with the general acceptance of particulate Mendelian inheritance during the development of modern genetics after 1900.
• 1859: Charles Darwin publishes The Origin of Species, which describes the theory of evolution by natural selection.  This theory requires heredity to work.
• 1866: Gregor Mendel publishes Experiments in Plant Hybridization, which lays out the basic theory of genetics.  It is widely ignored until 1900.
• 1871: Friedrich Miescher isolates “nucleic acid” from pus cells.
• Austrian Monk, born in what is now Czech Republic in 1822
• Austrian Monk Son of peasant farmer, studied Theology and was ordained priest Order St. Augustine.
• Austrian Monk

  Went to the university of Vienna, where he studied botany and learned the Scientific Method

  Worked with pure lines of peas for eight years

  Prior to Mendel, heredity was regarded as a "blending" process and the offspring were essentially a "dilution"of the different parental characteristics. 
• Mendel was the first biologist to use Mathematics – to explain his results quantitatively.

  Mendel predicted

  The concept of genes

  That genes occur in pairs

  That one gene of each pair ispresent in the gametes
• Theory of Pangenesis

  This theory, proposed by the famous English naturalist Charles Darwin (1809-1882), states that very small, exact but invisible copies of each body organ and component (called gemmules) are transported by the blood stream to the sex organs. 
• These gemmules are assembled in the gametes. After fertilization these gemmules move out to different parts of the body resulting in the development of respective organ
• Germplasm Theory; This theory, advocated by August Weismann (1889), a German biologist, states that body tissues are of two types,; germplasm and somatoplasm.
• The germplasm refers to the reproductive tissues or cells which produce gametes. The somatoplasm includes all other body tissues which are not related to sexual reproduction. Thus, transmission of characters from one generation to other takes place only through germplasm. 
• Any change in the germplasm will lead to change in the next generation. This theory is accepted in a broad sense
• friedrich miescher publishes his discovery of nuclei
• friedrich miescher he had isolated an acidic, phosphorus-rich component from the nuclei of white cells which he is harvested in pus. he called the substance nuclei, renamed nuclei acid
• Thomas Hunt Morgan Studied fruit fly eye color, determining that trait was sex-linked Won the Nobel Prize in 1933 for his work on chromosomes and genetics
• Thomas Hunt Morgan

  By this point, it was known that genetic material was located on a chromosome

  This genetic material was in discrete units called genes
• Thomas Hunt Morgan

  It was NOT known whether the gene was simply a protein, or whether it was composed of DNA
• 1926: Hermann J. Muller shows that X-rays induce mutations.
• 1944: Oswald Avery, Colin MacLeod and Maclyn McCarty show that DNA can transform bacteria, demonstrating that DNA is the hereditary material.
• 1953: James Watson and Francis Crick determine the structure of the DNA molecule, which leads directly to knowledge of how it replicates
• Used wire models to conform with the measurements that Franklin and Wilkins had come up with

  Determined the structure to be a double helix
• Lead to understanding of mutation and relationship between DNA and proteins at a  molecular level

  1959 – “Central Dogma”