AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

PRE - MENDELIAN IDEAS ON HEREDITY

• As early as the sixth century B.C., Greek philosophers had begun to search for explanations of how and why the world and human beings came to be formed and organized as they were.
• The work of Socrates (470-399 B.C.), Plato (429-347 B.C.), and Aristotle (384-322 B.C.) established the foundations of Western philosophy.
• Pythagoras (570-495 B.C.) proposed the theory that animals are born from one another by seeds and that seed is a drop from the brain which contains in itself a warm vapour; and that when this is applied to the womb, it transmits virtue, and moisture, and blood from the brain, from which flesh, and sinews, and bones, and hair, and the whole body are produced. And from the vapour is produced the soul, and also sensation.
  • Pythagoras was one of the first to elaborate a theory of generation, the biological production of offspring.
• According to Aristotle, the female parent contributed only unorganized matter to the new individual while the male provided the form.
• Jan Swammerdam made observations using microscopes in the late 17^th century, and interpreted their findings to develop the preformation theory, supposing that an egg contained all the future generations of its kind as preformed miniatures.
• William Harvey (1578-1657), in his publication the generation of animals (1651) argue that all living beings arose from eggs.
• Dutch microscopist Antonie van Leeuwenhoek (1932-1723) was one of the first to observe spermatozoa.He reasoned that the movement of spermatozoa was evidence of animal life, which presumed a complex structure and, for human sperm, a soul.
• In 1694, Nicolas Hartsoeker produced an image of tiny men inside the sperm, which he called " animalcule" or "homunculus ".
• Carl Linnaeus (1707-1778) Swedish naturalist and explorer was the first to frame principles for defining natural genera and species of organisms and to create a uniform system for naming them (binomial nomenclature).
• Lamarck (1744–1829) pioneer French biologist who is best known for his idea that acquired characters are inheritable, an idea also known as Lamarckism, and which is controverted by modern genetics and evolutionary theory.
• Lamarckism or Lamarckian evolution refers to the once widely accepted idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring (also known as based on heritability of acquired characteristics or "soft inheritance"). Lamarck stressed two main themes in his biological work.
  • The first was that the environment gives rise to changes in animals.
  • The second principle was that life was structured in an orderly manner and that many different parts of all bodies make it possible for the organic movements of animals. It proposed that individual efforts during the lifetime of the organisms were the main mechanism driving species to adaptation, as they supposedly would acquire adaptive changes and pass them on to offspring.
• Charles Robert Darwin (1809-1882) English naturalist and founder of modern evolutionary theory proposed and provided scientific evidence that all species of life have evolved over time from common ancestors through the process which he called Natural Selection.
  • Darwin found that those organisms more suited to their environment were more likely to survive. This resulted in the well known phrase survival of the fittest.
  • Pangenesis was Charles Darwin's hypothetical mechanism for heredity. Gemmules, also called plastitudes or pangenes, were assumed to be shed by the organs of the body and carried in the bloodstream to the reproductive organs where they accumulated in the germ cells or gametes.
  • They thus provided a possible mechanism for the inheritance of acquired characteristics, as proposed by Jean-Baptiste Lamarck.
• Regnier De Graaf is famous for having discovered the ovarian follicle (which is named Graafian follicle in his honour).
• A new way of thinking about heredity, fertilization, and development was made possible by the establishment of the Cell Theory in the 1830s.
• The establishment of cell theory is generally attributed to Matthias Jacob Schleiden (1804-1881) and Theodor Schwann (1810-1882), who recognized the importance of Robert Brown's (1773-1858) discover of the cell nucleus.
• Further investigations during the last quarter of the nineteenth century provided many insights into the role played by the nucleus during cell division, and the recognition of fundamental cytological phenomena such as mitosis, maturation, and fertilization and important cellular organelles, such as mitochondria, chloroplasts, and the Golgi apparatus.
• Cytological studies led to the discoveries that linked cytology to inheritance and development.
• Based on these studies, Friedrich Leopold August Weismann (1834-1914) proposed the theory of the continuity of the germplasm and predicted the reduction division of the chromosomes during the formation of the germ cells. He advocated the germ plasm theory, according to which (in a multicellular organism) inheritance only takes place by means of the germ cells -the gametes such as egg cells and sperm cells. -
• In Cell-Formation and Cell-Division (1875) Eduard Strasburger (1844-1912) described the division of plant cells.
• Walter Flemming's (1843-1905) Cell Substance, Nucleus, and Cell Division (1882) established a basic framework for the stages of cell division. Flemming used the term chromatin for the nuclear substance and coined the term mitosis.
• Heinrich W.G. Waldeyer (1836-1921) introduced the term chromosome in 1888.