Genetics Chapter Notes 1 & 2
Genetics Chapter Notes 1 & 2 Biol 3166
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This 6 page Bundle was uploaded by Jenna Nicole on Thursday September 8, 2016. The Bundle belongs to Biol 3166 at University of North Carolina - Charlotte taught by Dr. Steck in Fall 2016. Since its upload, it has received 6 views. For similar materials see Genetics in Biology at University of North Carolina - Charlotte.
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Date Created: 09/08/16
Genetics Fall 2016 Dr. Steck Chapter 1 Notes New findings in and applications in genetics can often have both significant economics and ethical implications which makes the study of genetics relevant, timely and interesting. All of us possess genes that influence our lives in significant ways. Genes affect our height, weight, hair color and skin pigmentation as well as influencing our susceptibility to many diseases and disorders. Genes even contribute to our personality and our intelligence, as a result, genes are fundamental to who and what we are. The Green Revolution which began in the 50’s and 60’s relied quite heavily on the application of genetics. Today genetically engineered corn, soybeans as well as other crops are responsible for a significant proportion of the food produced worldwide. Genetics play a very important role in the pharmaceutical industry as numerous drugs and food additives are synthesized by fungi and bacteria that have been genetically manipulated to make them efficient producers of such substances. Genetics also plays a very critical role in medicine as physicians now realize that many diseases and disorders have a hereditary component, not only the rare diseases or disorders but things such as asthma, hypertension and diabetes. Advances in the field of genetics has resulted in important insights into the nature of diseases such as cancer and in the development of diagnostic tests including those that identify pathogens and defective genes. The direct alternation of genes known as gene therapy has now been administered to thousands of patients although the use of gene therapy is still experimental and limited. “Genetics provides one of biology’s unifying principles: all organisms use genetic systems that have a number of features in common.” pg. 4 “Despite their tremendous diversity, living organisms have an important feature in common: all use similar genetic systems.” pg. 4 The complete set of genetic instructions for any organism is its genome All genomes are encoded in nucleic acids -either RNA of DNA. The coding system for genomic information is common to all life and all genetic instructions are in the same format. With rare exceptions, the code words are also identical. The processes by which genetic information is copied and decoded are also remarkably similar for all forms of life. These common features of heredity also suggest that all life on Earth evolved from the same primordial ancestor that arose 3.5 billion and 4 billion years ago. Richard Dawkins the biology describes life as a river of DNA that runs through time connecting all organisms past and present. The simple fact that all organisms have similar genetic systems means that the study of one organism’s genes reveals principles that apply to other organisms. The similarity of genetic systems also unfortunately is the basis for diseases such as AIDS in which viral genes are able to function with alarming efficiency sometimes in human cells. Both life’s diversity and adaptation are products of evolution which really is simply just genetic changes over time. Evolution is a two-step process in which inherited differences arise randomly and then the proportion of individuals with particular differences either increase or decrease. Genetic variation is the the foundation of all evolutionary changes and ultimately the basis of all life as we know it. The study of genetics is comprised of three subdisciplines: transmission genetics, molecular genetics and population genetics. Transmission genetics (known as classical genetics)- encompasses the basic principles of heredity and how traits are passed from one generation to the next Molecular genetics- concerns the chemical nature of the gene itself: how genetic information is encoded, replicated and expressed. Population genetics- explores the genetic composition of groups of individuals of the same species (populations) and how that composition changes over time and space. Because evolution is genetic change, population genetics is fundamentally the study of evolution. Throughout the year’s genetic studies have been conducted on thousands of different species including almost all of the major groups of fungi, bacteria, protists, animals and plants. During these studies a few species would emerge and become model genetic organisms. Model genetic organisms are organisms with characteristics that make them particularly useful for genetic analysis and from them a tremendous amount of genetic information has accumulated. Six model organisms which have been the subject of extensive genetic studies are Drosphila melanogaster (fruit fly), Escherichia coli ( bacteria present in the gut of humans and animals), Caenorhabditis elegans, ( a nematode also called a roundworm), Arabidopsis thaliana (thale cress plant), Mus musculus (the house mouse), and Saccharomyces cerevisiae (bakers yeast). These species are the organisms of choice for many researchers and their genomes were sequenced as a part of the Human Genome Project. Other species frequently subjected to genetic research include Neurospora crassa (bread mold), Zea mays (corn), Danio rerio (zebrafish), and Xenopus laevis (clawed frog). The value of model genetic organisms has been illustrated by use of zebrafish to identify genes that affect skin pigmentation in fish. “The first evidence that people understood and applied the principles of heredity in earlier times is found in the domestication of plants and animals, which began approximately 10,000 and 12,000 years ago in the Middle East. The first domesticated organisms included wheat, peas, lentils, barley, dogs, goats and sheep. By 4000 years ago, sophisticated genetic techniques were already in use in the Middle East. The Assyrians abd Babylonians developed several hundred varieties of date palms that differed in fruit size, color, taste and time of ripening.” Concepts of heredity Pangenesis- Genetic information travels from different parts of the body to reproductive organs. Incorrect concept. Inheritance of acquired characteristics- Acquired traits become incorporated into hereditary information. Incorrect concept. Preformationism- Miniature organism resides in sex cells, thus all traits are inherited from one parent. Incorrect concept. Blending inheritance- Genes blend and mix. Incorrect concept. Germ-plasm theory- All cells contain a complete set of genetic information. Correct concept. Cell theory- All life is comprised of and cells arise only from cells. Correct concept. Mendelian Inheritance- Traits are inherited according to specific principles proposed by Mendel. Correct concept. Genetics Chapter 2 Notes Prokaryote a unicellular organism with a relatively simple cell structure Eukaryote a compartmentalized cell structure with components bound by intracellular membranes (may be unicellular or multicellular) Prokaryotes have two fundamentally different types of bacteria: Eubacteria (true bacteria) and archaea (ancient bacteria) Some genetic processes such as transcription (in archaea) is more related to eukaryotes than bacteria and archaea is actually closer evolutionary to eukaryotes than eubacteria Chromatin the complex of DNA and histone proteins For any cell to reproduce successfully, three fundamental events must take place: 1) Its genetic information must be copied 2) The copies of the genetic information must be separated from each other 3) The cell must divide Eukaryotic chromosomes are separated from the cytoplasm by the nuclear envelope and the nucleus has a highly organized internal scaffolding called the nuclear matrix that consists of a network of protein fibers The nuclear matrix maintains precise spatial relations among components of the nucleus and takes part in DNA replication, the expression of genes and the modification of gene products they leave the nucleus Humans have 46 chromosomes per cell constituting 23 homologous pairs (pg 21) Diploid cells that carry two sets of genetic information Haploid cells that are reproductive and even nonreproductive cells contain a single set of chromosomes are haploid Polyploid the cells of some organisms contain more than two sets of genetic information A functional chromosome has three essential elements: A centromere, a pair of telomeres and origins of replication The centromere is the attachment point for spindle microtubules which are filaments responsible for moving chromosomes during cell division *kinetochore is a protein which assembles the centromere* Chromosomes are classified into four types on the basis of the location of the centromere: Metacentric, submetacentric, acrocentric and telocentric Telomeres are the natural ends or tips of linear chromosomes and they protect and stabilize the chromosome ends (chromosome stability duh) Origins or replication are the sites at which DNA synthesis begins and they’re not easily observed by microscopy Sister chromatids are two initially identitical copies of chromosomes which are held together at the centromere and each sister chromatid consists of a single molecule of DNA Meiosis consists of two distinct processes Meiosis 1 and Meiosis 2, each of which includes a cell division The first division comes at the end of meiosis 1 and is termed the reduction division because the number of chromosomes per cell is reduced by half The second division which comes at the end of meiosis II differs from mitosis in that chromosome number has already been halved in meiosis 1 and the cell does not begin with the same number of chromosomes as it does in mitosis Meiosis 1 Prophase 1 is a lengthy stage in which the chromosomes form homologous pairs and crossing over takes place First the chromosomes condense, pair up and begin synapsis (a very close pairing association) Each homologous pair of synapsed chromosomes called a bivalent or tetrad consists of four chromatids The chromosomes become shorter and thicker during this time Crossing over is a process in which homologous chromosomes exchange genetic information also takes place during this time, crossing over generates genetic variation and is essential to for the proper alignment and separation of homologous chromosomes Chiasma (chiasmata) is the location where two chromosomes cross and the centromeres of the paired chromosomes move apart; the two homologs remain attached at each chiasma and near the end of prophase 1 the nuclear membrane breaks down and the spindle forms Metaphase 1 is initiated when homologous pairs of chromosomes align along the metaphase plate Anaphase 1 is marked by the separation of homologous chromosomes and the two chromosomes of a homologous pair are pulled toward opposite poles..though the homologous chromosomes separate, the sister chromatids remain attached and travel together Telophase 1 the chromosomes arrive at the spindle poles and the cytoplasm divides Meiosis 2 Interkinesis the period between meiosis 1 and II During interkinesis the nuclear membrane reforms around the chromosomes that are clustered at each pole and the spindle breaks down with the chromosomes relaxing and the cells then pass pass through prophase II during which the evens of interkinesis are reversed: chromosomes recondense, spindle reforms and the nuclear envelope once again breaks down *In interkinesis in some types of cells the chromosomes remain condensed and the spindle does not break down* The cells move directly from cytokinesis into metaphase II (similar to metaphase of mitosis), the individual chromosomes line up on the metaphase plate with the sister chromatids facing opposite poles In anapahase II the kinetochores of the sister chromatids separate and the chromatids are pulled to the opposite poles with each chromatid now a distinct chromosome. In telophase II the chromosomes arrive at the spindle poles and the nuclear envelope reforms around the chromosomes and the cytoplasm divides and the chromosomes relax and are no longer visible
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