Introduction to Genetics PDF

Introduction to genetics CH 1 Dr. Radhika Bhardwaj  Learning objectives By the end of the lectures related to introduction to genetics, you should be able to: ❖ Describe the scientific terms related to Genetics ❖ Distinguish the primary characteristics of gene...

Introduction to genetics CH 1 Dr. Radhika Bhardwaj  Learning objectives By the end of the lectures related to introduction to genetics, you should be able to: ❖ Describe the scientific terms related to Genetics ❖ Distinguish the primary characteristics of genes. ❖ Relate the structure of the chromosomes to their functions. ❖ Describe Novel Technologies for identifying genes. Genetics explains why organisms have certain traits ◦ How traits are passed from parent to offspring ◦ Relationship between genes and traits The Human Genome 5 1.1 Genetics Progressed from Mendel to DNA in Less Than a Century Mendel’s Work on Transmission of Traits Gregor Mendel, an Augustinian monk, conducted a decade- long series of experiments using pea plants.. The Chromosome Theory of Inheritance: Uniting Mendel and Meiosis About 20 years after his work was published, advances in microscopy allowed researchers to identify chromosomes and later also described chromosome behavior during two forms of cell division, mitosis and meiosis. Genetic Variation The Search for the Chemical Nature of Genes: DNA or Protein?  Chromosomes The DNA in living cells is contained within large structures termed chromosomes. Each chromosome is a complex of DNA and proteins An average human chromosome contains ◦ More than a 100 million nucleotides ◦ about 1,000 different genes Human cells have a total of 46 chromosomes, found in pairs  chromosome, one of the sex-determining chromosomes of D. melanogaster, showing the location of several genes. Chromosomes can contain hundreds of genes. A colorized image of human Chromosome theory of A colorized image of the human male chromosomes that have duplicated inheritance, which states that chromosome set. in preparation for cell division, as inherited traits are controlled visualized using a scanning electron Arranged in this way, the set is called a karyotype. by genes residing on microscope. chromosomes  Inherited Differences in Traits Are Due to Genetic Variation Genetic variation refers to differences in inherited traits among individuals within a population ◦ Example: White versus purple flowers ◦ Example: Black versus brown hair In some cases, genetic variation is very striking ◦ Members of the same species may be misidentified as belonging to different species ◦ Morphs – contrasting forms within a single species Trait – any characteristic that an organism displays Affect the appearance of the organism Morphological traits Example: The color of a flower Affect the function of the organism Physiological traits Example: Ability to metabolize a sugar Affect the ways an organism responds to the environment Behavioral traits Example: Mating calls of bird species Genetic variation results from different kinds of changes at the molecular level Gene mutations Heritable changes in gene sequence Can alter the expression of function of a protein Changes in chromosome structure Large segments of the chromosome may be lost or rearranged Changes in chromosome number One chromosome lost or gained Whole set of chromosomes lost or gained Traits Are Governed by Genes and the Environment Traits cannot be explained by genes alone Traits result from the interaction between genes and the environment Called the norm of reaction Example: Diet has an effect on height, weight and even intelligence Environment may control whether a genetic disease is manifested Example: Phenylketonuria Phenylketonuria (PKU) 1 Phenylalanine hydroxylase enzyme Humans need one or two functional copies of the gene to metabolize phenylalanine Humans with two copies of a rare inactive allele cannot metabolize phenylalanine ◦ Phenylalanine accumulates, causing a number of detrimental effects ◦ Can cause mental impairment 12 Phenylketonuria (PKU) 2 Newborns are now screened for PKU Individuals with PKU are put on a strict diet low in phenylalanine ◦ Controlled diet allows normal development 13 1.2 Discovery of the Double Helix Launched the Era of Molecular Genetics The Structure of DNA and RNA , Gene Expression: From DNA to Phenotype Proteins and Biological Function Linking Genotype to Phenotype: Sickle-Cell Anemia P P P P P P P A single-nucleotide change in the DNA encoding β@globin (CTC S CAC) leads to an altered mRNA codon Normal red blood cells (round) and (GAG S GUG) and the insertion of a different amino acid sickled red blood cells. The sickled cells (Glu S Val), producing the altered version of the β@globin block capillaries and small blood vessels. protein that is responsible for sickle-cell anemia. 1.3 Development of Recombinant DNA Technology Began the Era of DNA Cloning Researchers discovered: Restriction enzymes (used by bacteria to cut and inactivate the DNA of invading viruses, could be used to cut any organism’s DNA at specific nucleotide sequences, producing a reproducible set of fragments). 1.4 The Impact of Biotechnology Is Continually Expanding The use of recombinant DNA technology and other molecular techniques to make products is called biotechnology. In the united states, biotechnology has quietly revolutionized many aspects of everyday life; products made by bio- technology are now found in the supermarket, in health care, in agriculture, and in the court system. Plants, animals, and the food supply -Genetically modify crop plants -Genes for traits including resistance to herbicides, insects, -Genes for nutritional enhancement have been introduced into crop plants. -The transfer of heritable traits across species using recombinant DNA technology creates transgenic organisms. -Herbicide-resistant corn and soybeans were first planted in the mid-1990s, and transgenic strains now represent about 88 percent of the U.S. Corn crop and 93 percent of the U.S. Soybean crop. It is estimated that more than 70 percent of the processed food in the united states contains ingredients from transgenic crops. Biotechnology in Genetics and Medicine  Genetic Technology New genetic technologies are useful and sometimes controversial Mammalian cloning ◦ 1997, Dolly the sheep was cloned ◦ 2002, Carbon copy (or “Copycat”) ◦ Cloned livestock could benefit farmers ◦ Human cloning has been legally banned Dolly the sheep was cloned by nuclear transfer, a method in which the nucleus of an adult cell is transferred into an egg that has had its nucleus removed. This method makes it possible to produce dozens or hundreds of genetically identical offspring with desirable traits and has many applications in agriculture, sports, and medicine. Dolly the sheep Carbon copy 18 R. Scott Horner KRT/Newscom Texas A&M University/Getty Images The human chromosome set, showing the location of some genes whose mutant forms cause hereditary diseases. Conditions that can be diagnosed using genetic testing are indicated by a red dot. 1.5 Genomics, Proteomics, and Bioinformatics Are New and Expanding Fields As more genome sequences were acquired, several new biological disciplines arose. -genomics (the study of genomes), studies the structure, function, and evolution of genes and genomes. -proteomics, identifies the set of proteins present in a cell under a given set of conditions, and studies their functions and interactions. To store, retrieve, and analyze the massive amount of data generated by genomics and proteomics, a specialized subfield of information technology called bioinformatics was created to develop hardware and software for processing nucleotide and protein data.  1.6 Genetic Studies Rely on the Use of Model Organisms Geneticists gradually came to focus attention on a small number of organisms, including the fruit fly (Drosophila melanogaster) and the mouse (Mus musculus). This trend developed for two main reasons: first, it was clear that genetic mechanisms were the same in most organisms, and second, these organisms had characteristics that made them especially suitable for genetic research. They were easy to grow, had relatively short life cycles, produced many offspring, and their genetic analysis was fairly straightforward. Geneticists Focus on Model Organisms Model organisms – species studied by many researchers Can compare results Determine principles that could apply to other species Model species are easy to grow in the lab Examples: Escherichia coli – a bacterium Saccharomyces cerevisiae – yeast Drosophila melanogaster – fruit fly Caenorhabditis elegans – nematode Mus musculus – mouse Arabidopsis thaliana – a plant (a) CDC/ Peggy S. Hayes & Elizabeth H. White, M.S.; (b) Science Photo Library/Alamy Stock Photo; (c) janeff/iStockphoto/Getty Images; (d) Sinclair Stammers/Science Source; (e) G.K. & Vikki Hart/Getty Images; (f) WILDLIFE GmbH/Alamy Stock Photo 23 Model Organisms and Human Diseases The development of recombinant DNA technology and the results of genome sequencing have confirmed that all life has a common origin. Because of this, genes with similar functions in different organisms tend to be similar or identical in structure and nucleotide sequence. Fields of Genetics Transmission Molecular Population Genetics Genetics Genetics Transmission Genetics Explores Inheritance Patterns Examines how traits are passed from parents to offspring The conceptual framework was provided by Gregor Mendel in the 1860s ◦ Genetic determinants pass from parent to offspring as discrete units ◦ Now we know these are genes Mendel used genetic crosses ◦ Breed individuals and analyze traits of offspring Transmission Genetics – Example Questions How can two brown-eyed parents produce a blue-eyed child? Why do tall parents tend to have tall children, but not always? 27 Molecular Genetics Focuses on Biochemical Understanding Deals with molecular features of DNA and how these underlie gene expression ◦ Organization, control and function of genes ◦ Analysis of DNA, RNA and proteins Molecular geneticists often use a genetic approach ◦ Study mutant genes with abnormal function to infer the normal function of the gene ◦ Example: Loss-of-function mutation 28  Molecular Genetics Applications Molecular genetics interfaces with biochemistry, biophysics, cell biology Molecular genetic advances shed light on areas of transmission and population genetics Modern molecular technologies and computer-based approaches have wide-spread applications throughout different fields Population Genetics is Concerned with Genetic Variation and Evolution Population genetics is a subfield of genetics that deals with genetic differences within and among populations and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.  Population Genetics is Concerned with Genetic Variation and Evolution Mendel’s work gave insight into the nature of genes and transmission Darwin’s theory of natural selection provided an explanation for variation in characteristics Population geneticists have developed mathematical theories to explain the prevalence of certain alleles within populations of individuals Allele frequencies within a population are important The Science of Genetics Genetics is an experimental science Genetic TIPS – problem solving strategies In addition to learning foundational knowledge, develop your problem-solving skills. Genetic TIPS ◦ Topic, Information, and Problem-solving Strategy  1.7 We Live in the Age of Genetics Genetics, Ethics, and Society Genetics and its applications in bio- technology are developing much faster than the social conventions, public policies, and laws required to regulate their use. As a society, we are grappling with a host of sensitive genetics-related issues, including concerns about prenatal testing, genetic discrimination, ownership of genes, access to and safety of gene therapy, and genetic privacy. *homologous chromosomes, pairs of chromosomes that have the same genes but different alleles, inherited from the mother and the father.  Summary Points 1. Mendel’s work on pea plants established the foundation for the science of genetics. 2.Genes and chromosomes are the fundamental units in the chro- mosomal theory of inheritance. This theory explains that inherited traits are controlled by genes located on chromosomes and shows how the transmission of genetic information maintains genetic continuity from generation to generation. 3. Molecular genetics—based on the central dogma that DNA is a template for making RNA, which encodes the order of amino acids in proteins—explains the phenomena described by Mendelian genetics, referred to as transmission genetics. 4. Recombinant DNA technology, a far-reaching methodology used in molecular genetics, allows genes from one organism to be spliced into vectors and cloned, producing many copies of specific DNA sequences. 5. Biotechnology has revolutionized agriculture, the pharmaceutical industry, and medicine.  Summary Points 6. Genomics, proteomics, and bioinformatics are new fields derived from recombinant DNA technology. The Human Genome Project is one example of genomics. 7. The use of model organisms has advanced the understanding of genetic mechanisms and coupled with recombinant DNA technology, has produced models of human genetic diseases. 8. The effects of genetic technology on society are profound, and the development of policy and legislation to deal with issues derived from the use of this technology is lagging behind the resulting innovations.