Chapter 1

Chapter 1 - CELL - 205 - 01 Genetics Instructor- Meenakshi...

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Unformatted text preview: CELL - 205 - 01 Genetics Instructor- Meenakshi Vijayaraghavan Office 4006 Percival Stern Hall Phone - 862-3154 E-mail Office hours Wed (TAs) and Fri (Dr.V) 11:00AM -12:30PM or by appointment Time and place All class sessions will take place in Jones 102, including examinations. Class meets TR from 12:30 - 1:45PM. Semester examinations will be given during class time on Feb.12th, March 11th, Apr.10th and from 8:00AM - 12PM on May 9th. Textbook: GENETICS Analysis and Principles Robert J. Booker Second edition McGraw Hill Design of course Lecture format Three midterms (15% each) Final examination (55%) Credit lost for poor attendance and poor performance in home work Blackboard Syllabus, lectures, and occasional announcements will be posted on Tulane's Blackboard system. Lectures will be posted before class. Today's assignment (Jan. 15th) is Chapter 1 Overview of Genetics Chapter - 1 Outline of today's lecture Human Genome Project Relationship between genes and traits Fields of genetics INTRODUCTION What better way to start Genetics than with an overview of the Human Genome Project? Formally launched in 1990 Coordinated by the National Institutes of Health (NIH) and the Department of Energy (DOE) Carried out by scientists from around the world Project goals were to identify all the approximately 20,000-25,000 genes in human DNA, determine the sequences of the 3 billion chemical base pairs that make up human DNA, store this information in databases, improve tools for data analysis, transfer related technologies to the private sector, and address the ethical, legal, and social issues (ELSI) that may arise from the project. A "working draft" of the human genome sequence was completed in 2000 Nearly 3 billion nucleotides Accuracy greater than 99.99% The study of the human genome provides fundamental molecular details about our genetic make-up The knowledge gained from the Human Genome Project will lead to Improvements in the diagnosis, treatment and prevention of disease; molecular medicine Risk assessment - environmental pollutions Bioarchaeology, anthropology, evolution, and human migration DNA forensics (identification) Agriculture, livestock breeding, and bioprocessing While trying to understand genes and their function, scientists have developed many genetic technologies These genetic technologies are often controversial DNA fingerprinting Mammalian cloning DNA fingerprinting Not well-received at first Now a common tool of forensic science Mammalian cloning In 1997, Ian Wilmut and colleagues cloned the first mammal A sheep named Dolly Fears that the technology may be applied to humans led to legislative bans on human cloning Genetic technologies allow the modification of animals in various ways For example, mice can be made to glow green A jellyfish gene encoding a green fluorescent protein is introduced into lab mice Upon exposure to ultraviolet light, the mice emit a bright green color Transgenic organism Transgenic Rice The genetically modified "golden rice" has engineered to produce high levels of beta-carotene, a precursor to vitamin A. (Campbell et al, 2004, 12.6) THE RELATIONSHIP BETWEEN GENES AND TRAITS Genetics is the study of heredity and variation It is the unifying discipline in biology The central theme in genetics is the gene The gene may be defined as a unit of heredity Genes provide the blueprint that determines the traits of an organism Living Cells Are Composed of Biochemicals All cells are constructed from small organic molecules These are linked together by chemical bonds to form larger molecules Cells contain four main types of large molecules Proteins Nucleic acids Carbohydrates Lipids Nucleic acids, proteins and carbohydrates are termed macromolecules They are polymers constructed from smaller molecules called monomers Cellular structures form as a result of the interaction of molecules and macromolecules Each Cell Contains Many Different Proteins That Determine Cellular Structure And Function The characteristics of a cell largely depend on the proteins it produces Proteins are the "workhorses" of cells They have diverse biological functions Structural proteins Tubulin Aggregates to form microtubules Plays role in cell shape and movement Contractile proteins Myosin Plays role in muscle contraction Hormonal proteins Insulin Regulates the level of glucose in the blood A particularly important group of proteins are the enzymes Enzymes are biological catalysts Catabolic enzymes Involved in the breakdown of large molecules into smaller ones Provide energy for the activities of the cell Anabolic enzymes Involved in the synthesis of large molecules from smaller ones Provide components for the construction of the cell Deoxy Ribonucleic Acid (DNA) The genetic material in living organisms is deoxyribonucleic acid (DNA) DNA encodes the information required to synthesize all cellular proteins It is able to do so because of its molecular structure A gene is a linear sequence on the DNA molecule. Deoxyribonucleic Acid (DNA) DNA is a polymer of nucleotides Each nucleotide contains one nitrogenous base Adenine (A) Thymine (T) Cytosine (C) Guanine (G) The genetic information is stored in the linear sequence of these bases along the DNA molecule DNA Stores the Information for Protein Synthesis ATG GGC CTT AGC DNA Sequence Met Gly Leu Ser Protein Sequence TTT AAG CTT GCC DNA Sequence Phe Lys Leu Ala Protein Sequence The genetic information is stored in the linear sequence of these bases along the DNA molecule The DNA in living cells is contained within large structures termed chromosomes Human cells have a total of 46 chromosomes Each chromosome is a complex of DNA and proteins An average human chromosome contains More than a 100 million nucleotides 1000-2000 genes The Information Within the DNA Is Accessed During the Process of Gene Expression Gene expression occurs in two steps Transcription The genetic information in DNA is copied into a nucleotide sequence of ribonucleic acid (RNA) Translation The nucleotide sequence in RNA is converted (using the genetic code) into the amino acid sequence of a protein The Molecular Expression of Genes Within Cells Leads to an Organism's Outwardly Visible Traits A trait is any characteristic that an organism displays There are two main types of traits Morphological traits Affect the appearance of the organism Example: The color of a flower Physiological traits Affect the function of the organism Example: Ability to metabolize a sugar Traits are controlled, at least in part, by genes The relationship between genes and traits spans four levels of biological organization 1. Genes are expressed at the molecular level 2. Proteins function at the cellular level 3. Traits are observed at the organismal level 4. Genes/traits within a particular species can also be studied at the populational level a. Molecular level b. Cellular level c. Organismal level d. Populational level Inherited Differences in Traits Are Due to Genetic Variation Genetic variation refers to differences in inherited traits among individuals within a population For example: In petunias, white vs. purple flowers In some cases, genetic variation is very striking Members of the same species may be misidentified as belonging to different species Garter snakes Contrasting forms within a single species are termed as morphs Genetic variation is a result of various types of changes at the molecular level 1. Gene mutations Small differences in gene sequences Lead to two or more alleles of the same gene 2. Changes in chromosome structure Large segments of the chromosome may be lost or duplicated 3. Changes in chromosome number Single chromosomes may be lost or gained A whole set of chromosomes may be inherited Traits Are Governed by Genes and by the Environment The traits an individual expresses often do not result from its genes alone Rather, traits are a result of the interaction between genes and the environment For example, an individual's diet has an effect on his/her height and weight In some cases, the environment dictates whether a disease is manifested in an individual or not Phenylketonuria (PKU) Humans contain a gene encoding the enzyme phenylalanine hydroxylase Converts phenylalanine to tyrosine Humans with one or two functional copies of this gene can metabolize phenylalanine Humans with two copies of a rare inactive allele cannot metabolize phenylalanine Phenylalanine will thus accumulate It ultimately causes a number of detrimental effects Mental retardation, for example PKU Newborns are now routinely screened for PKU Individuals with the disease are put on a strict dietary regimen Their diet is essentially phenylalanine-free These individuals tend to develop normally During Sexual Reproduction, Genes Are Passed from Parent to Offspring Gregor Mendel, in the mid-19th century, provided the foundation of the science of genetics The principles of inheritance he proposed can be explained by chromosomes and their behavior during cell division The union of sperm and egg during fertilization restores the diploid number Sexual reproduction enhances genetic variation It results in combinations of traits not found in either parent In humans, most cells have 46 chromosomes 23 homologous pairs Gametes Sperm and egg cells Are haploid Have 23 chromosomes The X and Y chromosomes of human males are not homologous The Genetic Composition of a Species Evolves Over the Course of Many Generations The genetic makeup of a population can change over time This is termed biological evolution Biological evolution is possible because of natural selection Natural selection can be summarized as such: Members of a species compete for essential resources In some individuals, random mutations lead to beneficial alleles Individuals are better adapted to the environment These individuals are more likely to survive and reproduce Therefore, the beneficial alleles are passed on to subsequent generations In addition, populations can harbor neutral mutations (unrelated to survival) Thus, genetic changes can accumulate These can slowly lead to remarkable modifications in the characteristics of a species Examples: The evolution of Equus caballus The modern day horse Important changes Larger size Fewer toes Modified jaw For grazing FIELDS OF GENETICS Genetics encompasses four biological disciplines Molecular Cellular Organismal Population Transmission genetics Molecular Genetics Population Genetics It is traditionally divided into three areas Transmission Genetics Explores the Inheritance Patterns of Traits as They Are Passed from Parents to Offspring Transmission genetics is the oldest field of genetics It examines how traits are passed from one generation to the next The conceptual framework was provided by Gregor Mendel in the 1860s Genetic determinants pass from parent to offspring as discrete units These are now termed genes The basic experimental approach is the genetic cross Two selected individuals are mated The traits in question are analyzed over several generations Analysis is often quantitative in nature Transmission genetics Mendelian patterns of inheritance Chromosomes and their roles in inheritance Complexities in transmission genetics Linkage Non-Mendelian patterns of inheritance Molecular Genetics Seeks a Biochemical Understanding of the Hereditary Material Molecular genetics is the most modern field of genetics It deals with the gene itself Its features, organization and function Molecular geneticists study "model organisms", such as Escherichia coli (a bacterium) Saccharomyces cerevisiae (a yeast) Drosophila melanogaster (an animal) Arabidopsis thaliana (a plant) The genes found in these organisms behave similarly as those in humans Molecular geneticists typically employ the genetic approach to research They study mutant genes that have an abnormal function Example: Loss-of-function mutation Molecular genetics Structure, replication, expression and regulation of the genetic material Mutations and rearrangements of the genetic material Recombinant DNA technology and computer-based approaches to studying the genetic material Role of the genetic material in human diseases Role of the genetic material in development Population Genetics Is Concerned With Genetic Variation and Its Role in Evolution Population genetics deals with the genetic composition of populations and how it changes over time and space It connects the work of Mendel on inheritance to that of Darwin on evolution Population genetics The role of the environment and genetics in the expression of traits How and why some alleles are maintained in populations The genetics behind the process of evolution Genetics Is an Experimental Science Science allows us to understand our natural world Genetics allows us to understand how genes produce traits The scientific method underlies scientific research It is a standard process that provides ways to validate (or invalidate) hypotheses about the natural world Finally, remember that science is a social discipline Think of it as a continuous dialogue! ...
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