Chapter 1: Origin & Importance of Genetics PDF

# Chapter 1: Origin & Importance of Genetics ## Biology - Study of life - Contains branches that deal with specific facets of life ## Genetics - Deals with the study of heredity - how organisms pass on information in their genes to create new generations of the same species, or variations of the...

# Chapter 1: Origin & Importance of Genetics ## Biology - Study of life - Contains branches that deal with specific facets of life ## Genetics - Deals with the study of heredity - how organisms pass on information in their genes to create new generations of the same species, or variations of the original. ## Development of the Science of Genetics - **8000-1000 BC:** Domestication of animals and cultivation of plants - **Greco-Roman Philosophy**: Hippocrates and Humorism; Middle Ages: William Harvey and Epigenesis; Theory of Preformation - **Charles Darwin and the Theory of Pangenesis** - **Gregor Mendel and the Dawn of Modern Genetics** - **Modern and Molecular Genetics** ### Aristotle and Vital Health; Greek Literature 5th & 4th BC - Greeks were tied to the idea of heredity because of the constant referral to lineages of kings and gods, and therefore, may have been the basis of the perceptions and theories on heredity and procreation "expressed by the ancient physicians and philosophers in the fifth and fourth centuries BC, which in turn influenced the development of genetics for many centuries". ### Hippocrates Humorism - Aristotle - Similar to Darwin's later ideas on pangenesis, involving heredity material that collects from throughout the body - Suggested that the physical characteristics of organisms are stored in the male semen that interacts with the female menstrual blood to form a new organism with fixed essence - Any variations arising from individuals are merely superficial ### Theory of Epigenesis - Harvey - Structures and organs of an organism only develop in the course of individual development - Has been the dominant opinion since antiquity until the 17th century ### Theory of Preformation - The entire organism is preformed in the sperm (animalkulism) or in the egg (ovism or ovulism) and only had to unfold and grow - **By Marcelo Malpighi** ## Theory of Pangenesis - **Charles Darwin** - Described the units of inheritance between parents and offspring and the processes by which those units control the development in offspring - Darwin coined the concept of gemmules - refers to hypothesized minute particles of inheritance thrown off by all cells of the body - Suggested that an organism's environment could modify the gemmules in any parts of the body, and that these modified gemmules would congregate in the reproductive organs of parents to be passed on to their offspring - Complements his Theory of Evolution via natural selection - suggested that all parts of the parents could contribute to the evolution and development of the offspring ## Gregor Mendel - An Augustinian monk (Johann Mendel) - Conducted the experiment of self and cross pollinations on the pea (Pisum sativum) at the monastery's garden - He presented his findings to the Natural Society of Brünn (1865) and the following year was published under the title "Experiments on Plant Hybridization" - **Laws of Inheritance** - During his time, the leading theory then was that traits blend from generation to generation "blended theory", how children look like depended on the phenotypic boundaries of the parents; but he deviated from this norm by conducting the experiment on the pea plant ### The Pea Experiment - The pea has a short growing period, easy to tend, and monoecious - Allowed Mendel to observe and follow easily observable characteristics of the plant up to two generations a year and allowed him to do self or cross pollination - Pea was a good choice because many varieties existed that differed from one another in clear-cut ways - Seven characteristics were observed - flower color and position, seed shape and texture, pod color and shape and stem length/height which only occurred in two distinct and no intermediate forms - When Mendel tried to cross a purebred pea with long stem, with a purebred short stem, all 1 filial generation (F1) offspring of this cross exhibited long stem, when F1 were crossed, a 3:1 ratio were observed: three parts with long stems and one with short stem; all other traits followed this general rule - 9:1 ratio after Fl is coolved - He concluded that inherited characteristics were carried in discrete, independent units - elementen (genes) and occur as pairs, these units are passed on to descendants unchanged and each parent contributed to one factor each to the offspring and may either be dominant or recessive - His first observations serve as the backbone of gene expression / | Character | Dominant | Recessive | |---|---|---| | Seed color | Yellow | Green | | Seed texture | Round | Wrinkled | | Pod color | Green | Yellow | | Pod shape | Full | Constricted | | Flower color | Purple | White | | Flower position | Axial | Terminal | | Stem height | Long | Short | ### Mendel's Findings - Dubbed as dominance and recessiveness - alleles can take one of two forms of the same character - the seed color can either be green or yellow and its texture either wrinkled or smooth - one is always dominant and is always expressed and the other recessive and is masked when it is with a dominant allele (heterozygous) - recessive traits can be expressed only when it is homozygous or paired with the same recessive factor - Determines the traits which are expressed by organisms - **Phenotype**: Determined by genotype - two organisms may look similar but may have different gene combinations - the phenotype of a purple flower is purple, regardless of the allele it contains (allelic combinations are referred to as its genotype) - thus a phenotypically purple flower may have a homozygous genotype (both dominant purple alleles) or a heterozygous purple (one dominant purple allele masking one recessive white allele) - Owing to these observations and inferences, Mendel continued on two fundamental principles of classic genetics: **Principle of Segregation** and **Principle of Independent Assortment** - **Principle of Segregation** - For a trait, a pair of allele separate and only one allele passes from parent to offspring - This separation produces gametes in the process of meiosis and by chance, the sperm and egg unite one allele from each parent at fertilization - **Principle of Independent Assortment** - Traits must sort into gametes separately and the inheritance of one is not affected by the other (independent) - He used plants that were homozygous for two characteristics such as seed color and seed shape - F1 generation were indistinguishable from the parents (3:1), F2 generation produced a ratio of 9:3:3:1: - 315 plants with round yellow seeds - 108 plants with round, green seeds - 101 plants with wrinkled, yellow seeds - 32 plants with wrinkled, green seeds - 9:3:3:1 - This principle explains why the inheritance of dark skin in humans does not increase or decrease the inheritance of a particular blood type. - **F2 9:3:3:1** - Findings of Gregor Mendel are the foundations of modern-day genetics (except for genetic linkage and intermediate dominance); pioneered the genetic trend in biology and established the global pursuit to map and better understand life's diversity through its genome, the totality of genes - Despite the ingenuity of his findings, the scientific community during his time had qualms on whether or not to accept the results - one of the reason was he used mathematics to analyze data, which was not a popular methodology during those times - he employed statistical tools to do away with observational biases and establish significant difference among his figures - After his death, several scientists did the same experiments on other organisms - **Thomas Hunt Morgan** - Used the fruit fly-Drosophila melanogaster - **Even with different organisms, findings still point out to the work of Mendel** ## Modern Genetics - **1905:** Hence, allowed the acceptance of Mendel's findings and he was named as the Father of Modern Day Genetics - **1905:** Genetics became a formal branch of biology when Willian Bateson coined the word "genetics" for the first time - **1905-1920:** Bateson and Punnett made significant findings on genetic linkages - **1944:** Historic experiment of Avery, MacLeod and McCarty on the Pneumococcus that elucidated the role of the DNA as the mediator of heredity - **1952:** Alfred Hershey and Martha Chase confirmed the findings of Avery, MacLeod and McCarty in their bacteriophage labelling experiments - **1953:** Most notable and recognizable historic development - James Watson and Francis Crick jointly proposed the double helix structure of the DNA - The structure is the foundation of many other scientific findings up to this day - Meselson and Stahl used equilibrium density gradient centrifugation to conclude that DNA replication is semi-conservative - **1958:** Fred Sanger developed the polymerase chain reaction (PCR) - **1986:** Dolly the sheep was born - first ever cloned animal from an adult somatic cell using the process of nuclear transfer - **1996:** Drosophila genome was completed - **2000:** CC the cat was born and was the first pet to be cloned - **2003:** The Human Genome Project (HGP) was completed - this was started in 1985 when Robert Sinsheimer pioneered discussions to sequence the human genome - **2006:** Sequence of the last remaining chromosome in the HGP was published in the journal Nature ## The Human Genome Project (HGP) - World's biggest collaborative research project that aimed to map the base pairs in the human genome - Although it was met with a lot of legal, ethical and social issues, the applications of the project were the ones boosted by the funding agencies and researchers, such as significant benefits to medicine and scientific research - Rheinberger (2002) said that "molecularizing disease and their possible cure will have a profound impact on what patients expect from medical help and the new generation of doctors' perception of illness" ## Cytogenetics - Just recently became a branch of genetics - Study of the number and structure of the chromosomes using microscopic analysis ## Molecular Genetics - Now a trend as scientists began to investigate at the cellular and subcellular level - Study of genes and chromosomes at the DNA molecule level using DNA technology - BBEE, BBER, BEE, BbEe, Bbee, bbEE, bbEe, bbee