Chapter 1 Introduction We Live in the Age of Genetics In December 1998 Iceland granted deCode Genetics a biotechnology company a license to create and operate a database drawn from medical records of all its 270 000 residents until 2012 This is a real example of the increasingly complex interaction of genetics and 1 1 Genetics Has a Rich and Interesting History 300 B C A D 1600 Few significant ideas were put forward to explain society heredity William Harvey Theory of epigenesist States that an organism develops from the fertilized egg by a succession of developmental events that eventually transform the egg into an adult This theory conflicted with the theory of preformation that each fertilized egg contained a homunculus Schleiden and Schwann 1830 The Cell Theory All organisms are composed of cells derived from preexisting ones Darwin Theory of Natural Selection Explained the mechanisms of evolutionary change Darwin began the very basic idea of inherited variation genetics however he lacked the key concepts of genetic variation and inheritance Mendel expanded the idea of genetics by experimenting with pea plants And exploring how traits are passed down from generation to generation Genetics Book definition the branch of biology concerned with the study of inherited variation Sutton and Boveri 1900 The chromosomal theory of inheritance States that inherited traits are controlled by genes residing on chromosomes inherited traits are controlled by genes residing on chromosomes faithfully transmitted through gametes maintaining genetic continuity from generation to generation 1 2 Genetics Progressed from Mendel to DNA in Less Than a Century Advances in microscopy have identified chromosomes Figure 1 2 and establish that most eukaryotes are diploid 2n two sets of chromosomes Diploid Book definition the condition in which each chromosomes exists in pairs Chromosomes in diploid cells exists in pairs called homologous chromosomes Book definition chromosomes that synapse or pair during meiosis and that are identical with respect to their genetic loci and centromere placement You are given a metaphase chromosome preparation a slide from an unknown organism that contains 12 chromosomes Two that are clearly smaller than the rest appear identical in length and centromere placement Answer Homologous chromosomes Human diploid number 46 Genes are transmitted through gametes This transmission maintains genetic continuity from generation to generation Genes are the functional unit of heredity A chromosome is composed of DNA complexed with proteins and many genes are found along the length of a single chromosome Alternate forms of a gene are called alleles Book definition one of the possible alternative forms of a gene often distinguished from other alleles by phenotypic effect That is alleles for various eye colors Variations in genes alleles DNA sequences are the result of mutations Book Definition heritable changes in the DNA sequence Mutations are the source of genetic variation Mutations produce alleles of a gene Genotype The set of alleles for a given trait Book Definition the allelic or genetic constitution of an organism The expression of the genotype produces an observable trait or phenotype Book Definition the overt appearance of a genetically controlled trait A lot of controversy was being produced when scientists were trying to figure out what carried genetic variation Avery MacLeod and McCarty 1944 DNA nucleic acid not protein is the carrier of genetic information 1 3 Discovery of the Double Helix Launched the Era of Molecular Genetics Watson and Crick 1953 DNA is an antiparallel double stranded helix Monomer nucleotide Book definition in nucleic acid chemical nomenclature a nucleoside covalently linked to 1 of more phosphate groups Sugar bonded to a phosphate and four bases Adenine cytosine guanine and thymine These nucleotides form A T and G C complementary base pairing across the helix RNA nucleic acid is similar to DNA except that it is usually single stranded it has adenine cytosine and guanine but has uracil U in place of thymine T the sugar in RNA nucleotides is ribose instead of deoxyribose Transcription is the process by which the information on a DNA strand is transcribed into a messenger RNA mRNA Book Definition of Transcription It is the transfer of genetic information from DNA by the synthesis of complementary RNA molecule using a DNA template Book Definition of mRNA An RNA molecule transcribed from DNA and translated into the amino acid sequence of a polupeptide Transcription occurs in the nucleus The mRNA moves into the cytoplasm where it binds to a ribosome Book Definition A ribonucloprotein organelle consisting of 2 subunits each containing RNA and protein molecules Ribosomes are the site of translation of mRNA codons into the amino acid sequence of a polypeptide chain The information in the mRNA is translated into a protein translation Book Definition The derivation of the amino acid sequence of a polypeptide from the base sequence of an mRNA molecule in association with a ribosome of tRNA The genetic code consists of triplet nucleotides present in mRNA Book Definition of genetic code The deoxynucleotide triplets that encode the 20 amino acids or specify termination of translation Each triplet codon encodes for insertion of a specific amino acid into a growing protein chain Book Definition of codon A triplet of nucleotides that specifies a particular amino acid or a start or stop single in the genetic code There are 20 different amino acids commonly found in proteins Once a protein is made its action or location in a cell plays a role in producing a phenotype Enzymes are the largest category of proteins Book Definition serve as biological catalysts lowering the energy of activation in reactions and allowing cellular metabolism to proceed at body temperature Other proteins include hemoglobin insulin connective tissue actin and myosin This is known as the central dogma of genetics Figure 1 8 That DNA is a template for making RNA which in turns directs the synthesis of proteins explains how genes control phenotypes Mutations altering a gene may modify alter or even eliminate the protein s usual function and cause an altered phenotype A mutation in the gene encoding B globin causes Sickle Cell Anemia Causes hemoglobin molecules in red blood cells to polymerize when the blood s oxygen concentration is low forming long chains of hemoglobin that distort the shape of red
View Full Document
Unlocking...