GEN311-INTRODUCTION-TO-GENETICS.pdf

Our Lady of Fatima University skulls, and dried seeds) documents the College of Arts & Sciences successful domestication of animals. Department of Psychology Domestication (Wolves to Dogs, Horses,...

Our Lady of Fatima University skulls, and dried seeds) documents the College of Arts & Sciences successful domestication of animals. Department of Psychology Domestication (Wolves to Dogs, Horses, Camels, Oxen to Cow), a form of selective breeding. GEN311 – GENETICS DOMESTICATION & SELECTIVE INTRODUCTION TO GENETICS BREEDING Every living thing- plant or animal, microbe, or human being has a set of characteristics inherited from its parent or parents. Since the beginning of recorded history, people have wanted to understand how that inheritance is passed from generation to generation. Thus, Genetics is the key to understanding what makes an organism unique. It also covers the mechanisms of “Ancient Genetic Manipulation” heredity and variation, general knowledge of the nature and regulation of genes in an organism, the mechanisms of genetic GOLDEN AGE OF GREEK CULTURE transmission, and the sources of variation in (500 – 400 BC) individuals and populations. Hippocratic School of Medicine and goofedAristotle already thought of heredity. BACKGROUND “Humors” is viewed as carrier of The origins of genetics are to be found in hereditary traits, present in semen. Gregor Mendel’s memoir on plant “Disease Humors” carries congenital hybridization (1865). However, the word disorders/deformation. ‘genetics’ was only coined in 1906, to Badcell designate the new science of heredity. THE TERM GENETICS This chapter will give us an idea of how the vast field of genetics has developed over William Bateson the years. What was it then, what is it now, (1861 – 1926) used the and what it be? term genetics to designate “the science of heredity and GENETICS HAS A RICH AND variation.” INTERESTING HISTORY He was a Mendelian Archeological evidences (pictorial and used the word representations, preserved bones and genetics to refer to the 1 KL  chair that was created for him at Cambridge in 1906. He proposed the science of heredity based GENE on Mendel’s law be named as genetics Wilhem Johanssen, inspired by Hugo de during the 1906 3rd International Vries’ “pangene”. Conference on Plant Hybridization. MENDEL’S PLANT HYBRIDIZATION GENETICS Published in 1866. Branch of biology concerned with the study Rediscovered independently by following of genes, genetic variation, and heredity scientists: in organisms. Huge de Vries in Netherlands. Gene is a region of DNA that encodes Carl Correns in Germany. function. Erich von Tschermak in Austria. Genetic variation is the presence of W. Bateson, a defense of Mendel’s differences in sequences of genes between Principles of Heredity reconnected with individual organisms of a species. general questions of heredity. Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring. OTHER BREAKTHROUGHS Cell Theory (Schwann, Schleiden, GREGOR JOHANN Virchow) MENDEL Debunk of Spontaneous Generation (Louis Pasteur) Born in 1822 in Natural Selection (Charles Darwin) Czechoslovakia. Cell Division & Behavior of Became a monk at a Chromosomes (August Weisman) monastery in 1843. Taught biology and had interest in statistics. CHROMOSOMAL THEORY OF Also studied at the University of Vienna. INHERITANCE (EARLY 1900s OR 20TH CENTURY) CARL CORRENS, HUGO DE VRIES, & The chromosomal theory of inheritance ERICH VON TSCHERMAK was given by Theodor Boveri and Walter Sutton in 1902. The three scientists who rediscovered It is the fundamental theory of genetics. Mendel’s laws in 1900. According to this theory, Mendelian factors They were all working independently on are carried in the chromosomes. different plant hybrids, and came to the same conclusions about inheritance as Mendel. 2 KL  Former international meetings in hybridization became international THOMAS HUNT MORGAN (1866 – meetings in genetics. 1945) He worked on Drosophilia melanogaster EMERGENCE OF MOLECULAR (fruit fly). GENETICS The Mechanism of Mendelian Heredity (T.H. Morgan, A.H. Sturtevant, H.J. Muller, The connection of Genetics to & C.B. Bridges). Biochemistry started with George Beadle Fused the chromosomal theory and and Edward Tatum (genetic control of Mendelian Laws. biochemical reaction in Neurospora). But there are corrections, ex. Second law of ONE GENE-ONE ENZYME HYPOTHESIS Mendel. But Beadle and Tatum thought that protein The Theory of Genes was genes as genes are complex macromolecules and carries catalytic properties. GENETIC DISTANCE COULD BE CALCULATED ERWIN SCHRODINGER Then, these distances could be compared CHARACTERIZED GENE (1944) with physical irregularities directly observed in chromosomes under the Gene is an aperiodic crystal with microscope – gene mutation. exceptional properties (What is Life). Herman Muller pioneered the X-ray of D. In this context, Avery, MacLeod, and melanogaster and induced mutagenesis. McCarty (1944) purified DNA from dead virulent pneumococcus and transform non- virulent strain to virulent strain. MUTATION WAS DEFINED Local alteration of chromosomes; a THE RACE FOR DNA DOUBLE HELIX particular allele was transformed into one another, the mutant gene. Francis Crick and James Watson The chromosomal reinterpretation of discovered the model for the DNA genetics pluralized the operational molecule (Central Dogma of Molecular characterization of the gene as a unit of Biology). heredity. Rosalind Franklin – X-ray crystallographer GENETICS WAS INSTITUTIONALIZED Institutionalized = specialization. 3 KL CENTRAL DOGMA OF MOLECULAR BIOLOGY PCR Polymerase Chain Reaction CURRENT AND EMERGING TECHNOLOGIES Bioinformatics, Genomics, Proteomics. Third Generation Sequencing Metabarcoding/e-DNA barcoding. Oxford Nanoford Gene Therapy and Genetic Engineering 4 KL  Our Lady of Fatima University College of Arts & Sciences Department of Psychology ADVANTAGES OF PEA PLANTS FOR GENETIC STUDY GEN311 – GENETICS There are many varieties with distinct heritable features, or characters (such as flower color). MENDELIAN GENETICS Mating can be controlled. Each flower has sperm-producing organs Although (stamens) and an egg-producing organ inheritance of (carpel) biological traits has Cross-pollination (fertilization between been recognized for different plants) involves dusting one plant thousands of years, the with pollen from another. first significant insights into how it takes place only occurred about 155 years ago. In 1866, Gregor Johann Mendel published the results of a series of experiments that would lay the foundation of the formal discipline of genetics. GREGOR JOHANN MENDEL Born in 1822 in Czechoslovakia. Became a monk at a monastery in 1843. Taught biology and had an interest in statistics. Also studied at the University of Vienna. CARL CORRENS, HUGO DE VRIES, & Mendel chose to track only those characters ERICH VON TSCHERMAK that occurred in two distinct alternative The three scientists who rediscovered forms. Mendel's laws in 1900. He also used varieties that were true- They were all working independently on breeding (plants that produce offspring of different plant hybrids and came to the the same variety when they self-pollinate). same conclusions about inheritance as Mendel. 1 KL  MENDEL’S EXPERIMENT In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization. The true-breeding parents are the P generation. The hybrid offspring of the P generation are called the F1 generation. When F1 individuals self-pollinate or cross-pollinate with other F1 hybrids, the F2 generation is produced. MODERN GENETIC TERMINOLOGY MENDEL’S EXPERIMENT To analyze the monohybrid cross and (1) Law of Segregation Mendel’s first three postulates, we must (2) Law of Dominance and Recessiveness first introduce several terms: (3) Law of Independent Assortment Phenotype – Physical expression of a trait Genes – Mendel’s unit factors that represent a unit of inheritance. THE LAW OF SEGREGATION Allele – Alternative form of a single gene Mendel identified his first law of in a set of characters (ex. R or r). inheritance by following one character at Genotype – two unit factors present in an one time. individual, the genetic make up of an Crossing two true-breeding parents individual. (ex. RR, rr, or Rr). differing in one character produces a Homozygous – both alleles are the monohybrid in the F1 generation, same (ex. RR or rr). heterozygous* for both characters. Heterozygous – alleles are different A dihybrid cross, a cross between F1 (ex. Rr). dihybrids, can determine whether two characters are transmitted to offspring as a PUNNETT SQUARES package or independently. Mendel observed the pattern of six pea Used to easily visualize the genotypes and plant characters, each represented by two phenotypes resulting from the combining traits. gametes during fertilization. What Mendel called a “heritable factor” is Named after Reginald C. Punnett. what we now call a gene. 2 KL  THE LAW OF DOMINANCE & RECESSIVENESS When two unlike factors responsible for a single character are present in a single individual, one unit factor is dominant to the other, which is said to be recessive. CONNECTION TO CHROMOSOME THEORY CONNECTION TO BEHAVIOR CHROMOSOME THE LAW OF INDEPENDENT ASSORTMENT Mendel identified his second law of inheritance by following two characters at the same time. Crossing two true-breeding parents differing in two characters produces 3 KL  dihybrids in the F1 generation, However, the basic principles of heterozygous for both characters. segregation and independent assortment A dihybrid cross, a cross between F1 apply even to more complex patterns of dihybrids, can determine whether two inheritance. characters are transmitted to offspring as a package or independently. EXTENDING MENDELIAN GENETICS FOR A SINGLE GENE The law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation. Strictly speaking, this law applies only to genes on different, non-homologous Inheritance of characters by a single gene chromosomes or those far apart on the same may deviate from simple Mendelian chromosome. patterns in the following situations: Genes located near each other on the same 1. When alleles are not completely chromosome tend to be inherited together. dominant or recessive. (Incomplete Dominance) CRITIQUE TO MENDEL’S LAWS: 2. When a gene has more than two INHERITANCE PATTERNS ARE alleles. (Principles of Multiple OFTEN MORE COMPLEX THAN Alleles – ex. ABO Blood Groups) PREDICTED BY SIMPLE 3. When a gene produces multiple MENDELIAN GENETICS phenotypes. (Codominance) The relationship between genotype and phenotype is rarely as simple as in the pea DEGREES OF DOMINANCE plant characters Mendel studied. Complete dominance occurs when Many heritable characters are not phenotypes of heterozygote and dominant determined by only one gene with two homozygote are identical. alleles. 4 KL  In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties. In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways. MULTIPLE ALLELES Most genes exist in populations in more than two allelic forms. For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i. The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither. 5 KL  Our Lady of Fatima University The exception is meiosis, a special type of College of Arts & Sciences division that can produce sperm and egg Department of Psychology cells. GEN311 – GENETICS CELLULAR ORGANIZATION OF THE GENETIC MATERIAL MITOSIS & MEIOSIS All the DNA in a cell constitutes the cell’s genome. THE KEY ROLE OF CELL DIVISION A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells). DNA molecules in a cell are packaged into chromosomes. Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division. Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus. Somatic cells (non-reproductive cells) The ability of organisms to produce more have two sets of chromosomes. of their own kind best distinguishes living Gametes (reproductive cells: sperm and things from nonliving matter. eggs) have half as many chromosomes as The continuity of life is based on the somatic cells. reproduction of cells, or cell division. In unicellular organisms, the division of one cell reproduces the entire organism. Multicellular organisms depend on cell division for Development from a fertilized cell, Growth, and Repair. Cell division is an integral part of the cell cycle —the life of a cell from formation to its own division. Most cell division results in genetically identical daughter cells. 1 KL DISTRIBUTION OF CHROMOSOMES DURING EUKARYOTIC CELL DIVISION In preparation for cell division, DNA is replicated, and the chromosomes are condensed. Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome), which separate during cell division. The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached. During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei. Once separate, the chromatids are called chromosomes. Eukaryotic cell division consists of: Mitosis, the division of the genetic material in the nucleus. Cytokinesis, the division of the cytoplasm. Gametes are produced by a variation of cell division called meiosis. 2 KL  Meiosis yields non-identical daughter cells that have only one set of chromosomes, half as many as the parent cell. PHASES OF THE CELL CYCLE The cell cycle consists of: Mitotic (M) phase (mitosis and cytokinesis) Interphase (cell growth and copying of chromosomes in preparation for cell division) Interphase (about 90% of the cell cycle) can be divided into subphases: G1 phase (“first gap”), S phase (“synthesis”), and G2 phase (“second gap”). The cell grows during all three phases, but chromosomes are duplicated only during the S phase. THE MITOTIC SPINDLE: A CLOSER LOOK The mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosis. In animal cells, the assembly of spindle microtubules begins in the centrosome, the microtubule organizing center. Mitosis is conventionally divided into five The centrosome replicates during phases (prophase, prometaphase, interphase, forming two centrosomes that metaphase, anaphase, and telophase). migrate to opposite ends of the cell during Cytokinesis overlaps the latter stages of prophase and prometaphase. mitosis. 3 KL  An aster (a radial array of short microtubules) extends from each centrosome. CYTOKINESIS: A CLOSER LOOK The spindle includes the centrosomes, the spindle microtubules, and the asters. During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes. Kinetochores are protein complexes associated with centromeres. At metaphase, the chromosomes are all lined up at the metaphase plate, an imaginary structure at the midway point between the spindle’s two poles. In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow. In plant cells, a cell plate forms during cytokinesis. In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell. The microtubules shorten by depolymerizing at their kinetochore ends. Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell. In telophase, genetically identical daughter nuclei form at opposite ends of the cell. Cytokinesis begins during anaphase or telophase and the spindle eventually disassembles. 4 KL  ASEXUAL REPRODUCTION Single-celled eukaryotes Yeast (fungi) Protists Paramecium Amoeba Simple multicellular eukaryotes Hydra Human Female Karyotype (46 Chromosomes, 23 Pairs) If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase. Human Male Karyotype (46 Chromosomes, 23 Pairs) MEIOSIS & SEXUAL REPRODUCTION 5 KL  Fertilization restores chromosome number. HOMOLOGOUS CHROMOSOMES Haploid (n) → diploid (2n) egg (n) + sperm (n) → (2n) 23 23 46 Paired chromosomes Both chromosomes of a pair carry “matching” genes Control same inherited characters Homologous = same information HOW DO WE MAKE SPERM & EGGS? MEIOSIS Must reduce 46 chromosomes → 23 Must half the number of chromosomes. MEIOSIS: PRODUCTION OF GAMETES Alternating processes/stages. Chromosome numbers must be reduced. Diploid (2n) → haploid (n) Humans: 46 → 23 Meiosis reduces chromosome Reduction Division number. Special cell division in sexually Makes gametes. reproducing organism 6 KL  Reduce 2n →1n Diploid → haploid (“half”) STEPS OF MEIOSIS Makes gametes (sperm, eggs) Warning: Meiosis evolved from mitosis, so Meiosis 1 stages and “machinery” are similar but the Interphase processes are radically different. Do not Prophase 1 confuse the two. Metaphase 1 Anaphase 1 DOUBLE DIVISION OF MEIOSIS Telophase 1 Meiosis 2 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 PREPARING FOR MEIOSIS 1st step of meiosis. Duplication of DNA Why? Meiosis evolved after mitosis. Convenient to use “machinery” of mitosis DNA replicated in S phase of interphase of MEIOSIS (just like in mitosis) 7 KL  MITOSIS VS. MEIOSIS PUTTING IT ALL TOGETHER 8 KL  TRADING PIECES OF DNA CROSSING OVER Crossing Over During Prophase 1, sister chromatids intertwine. Synapsis Homologous pairs swap pieces of chromosome. DNA breaks & re-attaches 3 steps Cross Over Breakage of DNA Re-fusing of DNA New combinations of traits (DNA Recombination). VARIATION FROM GENETIC RECOMBINATION Independent assortment of chromosomes. Meiosis introduces genetic variation. Gametes of offspring do not have same combination of genes as gametes from parents. Random assortment in humans produces 223 (8,388,608) different combinations in gametes. THE VALUE OF SEXUAL REPRODUCTION Sexual reproduction introduces genetic variation. Genetic recombination during meiosis. Independent assortment of chromosomes. 9 KL  Random alignment of homologous chromosomes in Meiosis 1. VARIATION FROM RANDOM Crossing over FERTILIZATION Random fertilization Sperm + Egg = ? Which sperm fertilizes which egg? Any 2 parents will produce a zygote Driving evolution with over 70 trillion (223 x 223) Variation for natural selection possible diploid combinations. VARIATION FROM CROSSING OVER Crossing over creates completely new combinations of traits on each chromosome. From 8 million different gametes → “immeasurable”. 10 KL