Genetics L1.pdf

"Chapter 1: Genetics and the Organism"  Genes as determinants of the inherent properties of species * Genes are the units of heredity that determine the inherent properties of a species. Genetics concerns with genes and their effects on all living organisms. Patterns of inheritance of tra...

"Chapter 1: Genetics and the Organism"  Genes as determinants of the inherent properties of species * Genes are the units of heredity that determine the inherent properties of a species. Genetics concerns with genes and their effects on all living organisms. Patterns of inheritance of traits. What makes a species what it is? We know that cats always have kittens and people always have babies. This commonsense observation naturally leads to questions about the determination of the properties of a species. The determination must be hereditary because, for example, the ability to have kittens is inherited by every generation of cats. What causes variation within a species? We can distinguish one another as well as our own pet cat from other cats. Such differences within a species require explanation.  History of Nucleic Acid Discovery Who is this scientist? Gregor Mendel “Father of Genetics” What is he known for? Mendel ’s Laws of Inheritance, 1865  So did Mendel discover Nucleic Acids? You have already covered Mendel’s Laws of Inheritance in BIO210 Pisum sativum  Discovering He discovered DNA and named it Nuclien nuclein. 1869 He is a Swiss medical doctor who dedicated his career in research instead of clinical practice. Why? Friedrich Miescher His experiments were on the chemical composition of Leukocytes. Biochemists at that time already knew the characteristics of : Lipids Leukocytes Proteins Carbohydrates In his experiments, Miescher noticed a precipitate from leukocytes of an unknown substance, with different properties to lipids and proteins: It was resistant to protease digestion. it contained large amounts of phosphorous Because it was from the NUCLEUS it lacked Sulphur. He named it NUCLEIN  Who is this scientist? History of Nucleic Acid Discovery Thomas Morgan Morgan worked with the red-eyed and white-eyed phenotypes in fruit flies and discovered sex-linked He is known for confirming the inheritance patterns which confirmed that “genes are located on chromosomes”. “Chromosome Theory of Inheritance” in 1910  History of Nucleic Acid Discovery Showed evidence of recombination between Chromosomes, 1931 She also discovered transposable elements. Barbara McClintock Start of Molecular Biology The studies just discussed tell us important aspects about “Transmission Genetics” What’s Transmission Genetics? The transmission of genes and how to map genes on chromosomes But! These studies do not tell us that genes are made of DNA and how it works!  Heredity?? Protein or DNA? Griffith’s Experiment Streptococcus pneumonia S-strain (smooth with capsule) R-strain (rough with no capsule) Conclusion: There is a chemical component in the R- strain that causes (virulence/death) and Is resistant to heat and can transform the R- strain. Oswald Avery Avery continued Griffith’s work (Using a process of elimination) he used hydrolytic enzymes. 1. Protease (hydrolyses protein) 2. DNAse ( hydrolyses DNA) 3. RNAse (hydrolyses RNA) Chase and Hershey 1952 they confirmed Avery’s results using bacteria and phage. Discovering Nucleic Acid Structure 1950 – Edwin Chargaff find Cytosine complements Guanine and Adenine complements Thymine. 1952-1953 James D. Watson and Francis H. C. Crick deduced the double helical structure of DNA. Three fundamental properties are required of genes and the DNA of which they are composed. 1. Replication. Hereditary molecules must be capable of being copied at two key stages of the life cycle. 2. Generation of form. The working structures that make up an organism can be thought of as form or substance, and DNA has the essential “information” needed to create form. 3. Mutation. A gene that has changed from one allelic form into another has undergone mutation—an event that happens rarely but regularly. Mutation is not only a basis for variation within a species, but also, over the long term, the raw material for evolution.  Genes as determinants of the inherent properties of species * Genes are made up of DNA, which is a molecule that contains the instructions for building proteins. An organism’s basic complement of DNA is called its genome. The somatic cells of most plants and animals contain two copies of their genome; these organisms are diploid. The cells of most fungi, algae, and bacteria contain just one copy of the genome; these organisms are haploid. The genome itself is made up of one or more extremely long molecules of DNA that are organized into chromosomes. Genes are simply the regions of chromosomal DNA that are involved in the cell’s production of proteins. DNA DNA is composed of two nucleotide chains held together by complementary pairing of A with T and G with C. DNA is replicated by the unwinding of the two strands of the double helix and the building up of a new complementary strand on each of the separated strands of the original double helix. Overview of gene expression How to get proteins? 1- The biological role of most genes is to carry information specifying the chemical composition of proteins or the regulatory signals that will govern their production by the cell. This information is encoded by the sequence of nucleotides. A typical gene contains the information for one specific protein. During transcription, one of the DNA strands of a gene acts as a template for the synthesis of a complementary RNA molecule.  Translation The process of producing a chain of amino acids based on the sequence of nucleotides in the mRNA is called translation. AUU CCG UAC GUA AAU UUG codon codon codon codon codon codon The information in genes is used by the cell in two steps of information transfer: DNA is transcribed into mRNA, which is then translated into the amino acid sequence of a polypeptide. The flow of information from DNA to RNA to protein is a central focus of modern biology Genes and environment * Proteins are the building blocks of cells and tissues, and they play a role in all aspects of an organism's life, including its growth, development, and metabolism. * The environment can also influence the expression of genes, which means that the same gene can produce different phenotypes (observable characteristics) in different environments. Genetic Variation * Genetic variation is the diversity of genes within a population. * Genetic variation is important for evolution, as it allows populations to adapt to changes in their environment. * There are two main types of genetic variation: heritable variation and non-heritable variation. * Heritable variation is passed from parents to offspring. * Non-heritable variation is not passed from parents to offspring. DISCONTINUOUS VARIATION A character is found in a population in two or more distinct and separate forms called phenotypes. “Blue eyes” and “brown eyes” are phenotypes, as is “blood type A” or “blood type O.” Such alternative phenotypes are often found to be encoded by the alleles of one gene. CONTINUOUS VARIATION A character showing continuous variation has an unbroken range of phenotypes in a population. Measurable characters such as height, weight, and skin or hair color are good examples of such variation. Molecular basis of allelic variation If the DNA of the tyrosinase-encoding gene changes in such a way that one of these crucial amino acids is replaced by another amino acid or is lost, then there are several possible consequences. First, the enzyme might still be able to perform its functions but in a less efficient manner. Second, the enzyme might be incapable of any function and cause the disease. Third, more rarely, the altered protein may perform its function more efficiently and thus be the basis for future evolution by natural selection.  The mutational site in the DNA can be : 1- The most common type is nucleotide-pair substitution, which can lead to amino acid substitution or to premature stop codons. 2- Small deletions and duplications also are common. 3- Such mutations are called frameshift mutations. Even a single base deletion or insertion produces widespread damage at the protein level; because mRNA is read from one end “in frame” in groups of three, a loss or gain of one nucleotide pair shifts the reading frame, and all the amino acids translationally downstream will be incorrect. MESSAGE New alleles formed by mutation can result in no function, less function, more function, or new function at the protein level.