AGRO/ANSC/BIO/GENE/HORT 305 Fall, 2016 Overview of Genetics Lecture outline (Chpt 1, Genetics by Brooker) #1 - Genetics: Progress from Mendel to DNA: Gregor Mendel, in the mid 19 th century provided the foundation of the science of genetics. - Mendel s work on transmission of traits: - Traits of living things are passed from parents to offspring in predictable ways. - Traits are controlled by discrete units of inheritance (genes). - Each trait is controlled by a pair of genes and the members of each gene pair separate from each other during the formation of egg and sperm. - During sexual reproduction, genes are passed from parents to offspring. - The principles of inheritance can be explained by the behavior of chromosomes during cell division. Genes are passed from parent to offspring as discrete units. - Sexually-reproducing species are diploid; they have two copies of each chromosome, one from each parent. - The two copies are termed homologues. - Homologues contain the same genes, but not necessarily the same alleles. - Gametes are haploid. - The union of sperm and egg during fertilization restores the diploid number. - Sexual reproduction enhances genetic variation combination of traits not found in either parent. - The genetic composition of a species evolves over the course of many generations. - The genetic composition 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 leads to beneficial alleles - These individuals are more likely to survive and reproduce - Therefore, the beneficial alleles are passed on to subsequent generations. - Thus, genetic changes can accumulate - These can slowly lead to remarkable modifications in the characteristics of a species. - Chromosome theory of Inheritance: - Members of each species have a characteristic number of chromosomes, called the diploid number (2n). - Chromosomes in diploid cells exist in pairs, called homologous chromosomes. - Behavior of chromosomes in two forms of cell division, mitosis and meiosis. In mitosis, chromosomes are copied and distributed such that each daughter cell receives a diploid set of chromosomes. Meiosis is associated with the formation of eggs and sperms and here the cells produced receive only one chromosome from each chromosome pair. 1
- Genes are carried on chromosomes, both occur as pairs and separate from each other during gamete formation. - Chromosome theory of inheritance states that inherited traits are controlled by genes residing on chromosomes that are faithfully transmitted through gametes, maintaining genetic continuity from generation to generation. - The relationship between genes and traits: - Genetics is the study of heredity and variation - it is a unifying discipline in biology. - The central theme in genetics is the gene. - The gene is a segment of DNA that produces a functional product. It is classically defined as the 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 breakage of chemical bonds provides energy, and they act as building blocks for the synthesis of larger molecules. - cells contain four main types of large molecules: Nucleic acids, Proteins, Carbohydrates, Lipids. - Nucleic acids, proteins and carbohydrates are polymers constructed from smaller molecules (monomers) and are termed 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 e.g. tubulin, which aggregates to form microtubules that play a role in cell shape and movement. - Contractile proteins e.g. Myosin, which plays a role in muscle contraction. - Hormonal proteins e.g. Insulin, which regulates the level of glucose in the blood. A particularly important group of proteins are the enzymes. - Enzymes are biological catalysts: - Catabolic enzymes - are involved in the breakdown of larger molecules into smaller molecules and provide energy for the activities of the cell. - Anabolic enzymes - are involved in the synthesis of larger molecules from smaller ones and provide components for the construction of cells. - DNA stores the information for protein synthesis: - 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. - DNA is a polymer of nucleotides. A nucleotide contains one nitrogenous base - Adenine (A) - Thymine (T) 2
- Cytosine (C) - Guanine (G) - 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 - Each chromosome is complex of DNA and proteins. - An average human chromosome contains more than 100 million nucleotides and contains 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 traits: - A trait is any characteristic that an organism displays - There are two main types of traits o Morphological - affect the appearance o Physiological - affect the function o Behavioral- affects response to environment. - The relationship between genes and traits spans 4 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 population level. - Inherited differences in traits are due to genetic variation: - Genetic variation refers to differences in inherited traits among individuals within a population, e.g. white versus purple petunias. - In some cases, genetic variation is very striking. o Members of the same species may be misidentified as belonging to different species. Contrasting forms within the same 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. a. Different alleles of a gene have different DNA sequences. b. An example is eye color in humans. The gene is for eye pigmentation, the alleles of the gene determine the color, and different eye colors are produced by different alleles. 3
2. Changes in chromosome structure: large segments of the chromosome may be deleted or duplicated 3. Changes in chromosome number: single chromosomes may be lost or gained; a whole set of chromosomes may be inherited o Down syndrome extra chromosome 21 - 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. - In some cases, the environment dictates whether a disease is manifested in an individual or not. An example of this kind is the disease phenylketonuria. - Development of Recombinant DNA Technology - This era began in the early 1970s, when researchers discovered that bacteria protect themselves from viral infection by producing enzymes that cut viral DNA at specific sites. Scientists quickly realized that such enzymes called restriction enzymes, could be used to cut any DNA at specific sites producing reproducible set of fragments. This set the stage for the development of DNA cloning or making many copies of the DNA sequences. - Soon scientists developed methods to insert the DNA fragments into carrier DNA molecules called vectors to make recombinant DNA molecules and transfer them into bacterial cells. As the bacterial cells reproduce, thousands of copies or clones of combined vector and DNA fragments are produced. Once large quantities of specific DNA fragments become available, they can be used for further characterization. - - Development of genetic technologies - Gene cloning - DNA fingerprinting - Gene therapy - Mammalian cloning (the first clone, a sheep named Dolly); legislative bans on human cloning. - GMOs (Genetically modified organisms) - Recombinant DNA technology has led to the characterization of entire genomes which has resulted in the field of genomics. - Recombinant DNA technology has given rise to the biotechnology industry, which has grown over the last 25 years to become a major contributor to the US economy. - Creating a genome from scratch - Biotechnology - Biotechnology has revolutionized many aspects of everyday life. - It has allowed us to genetically modify organisms in new ways and use their products to enhance our lives. - Biotechnology is the use of these modified organisms or their products 4
- The genetic modification of crop plants is one of the most rapidly expanding areas of biotechnology. - This agricultural transformation is a source of controversy. - Biotechnology in Genetics and Medicine. o Genetic testing and gene therapy, already an important part of medicine will be a leading force deciding the nature of medical practice in the 21 st century. o Genes for many disorders have been isolated and cloned and are now used in genetic tests. o Instead of testing one gene at a time, a new technology is being developed that will allow screening the entire genome for any possible genetic defect. This technology uses devices called DNA microarrays or DNA chips. o In gene therapy, normal genes are transferred into individuals affected with genetic disorders. Genomics, Proteomics, and Bioinformatics: Genomics: - Laboratories around the world have initiated projects to sequence and analyze genomes of different organisms including those that cause human diseases. To date the genomes of over 550 organisms have been sequenced. - As genome projects multiplied, several new biological disciplines arose. One called genomics, sequences genomes and studies the structure, function and evolution of genes and genomes. - Human Genome Project Coordinated by NIH (National Institute of Health) and DOE (Department of Energy) Started in 1990. Genome is the DNA found in all the chromosomes. o The complete sequence of the genome was completed in 2000. o Each cell has 46 chromosomes o 2 meters of DNA o Nearly 3 billion nucleotides o Approximately 35,000 genes o The knowledge from the human genome project will lead to improvements in the diagnosis and treatment and prevention of diseases. Proteomics: - It identifies the set of proteins present in a cell under certain conditions, studies the post-translational modification of these proteins, their location within the cells, and the protein-protein interactions occurring in the cell. Bioinformatics: - 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 the data. Medical Genetics: 5
- Inherited pattern of genetic diseases - Genetic screening - Genetic basis of cancer Fields of Genetics: - 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. - Molecular genetics seeks a biochemical understanding of the hereditary material - molecular genetics is the most modern field of genetics. - It deals with the gene - its features, organization and function Involves study of mutant genes that have abnormal function, like elimination of gene function, loss-of-function mutation - genetic approach. - 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 Mendelian concepts to that of Darwin s concept on evolution - Genomics: refers to the molecular analysis of the entire genome of a species (genome: genetic composition of an organism) - Structural genomics: mapping and sequencing of genomes - Functional genomics: the roles of genetic sequences in a given species Genetics is an experimental science - The scientific method underlies scientific research: two general types of scientific approaches : o Hypothesis testing o Discovery-based - Finally, remember that science is a social discipline think of it as a continuous dialogue! We live in the age of Genetics - The Nobel Prize and Genetics: Although other scientific disciplines have also expanded in recent years, none has paralleled the explosion of information and excitement generated by the discoveries in Genetics. Nowhere, is this impact more apparent than in the list of Nobel prizes in the fields of medicine and chemistry. - Genetics and Society: The impact of this discipline on society has never been more profound than it is today. Genetics and its applications in biotechnology 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 issues like prenatal testing, insurance coverage, genetic discrimination, ownership of genes, access and safety to gene therapy, genetic privacy and genetically modified organisms. 6
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