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PROGETTO ORIENTAMENTO IN RETE CORSO DI BIOLOGIA In Inglese Prof.ssa LONGO UD 4 1 Law of Segregation • Organisms inherit two copies of each gene, one from each parent • Organisms donate only one copy of each gene in their gametes • Two copies of each gene segregate, or separate, during gamete formation Segregation and Inheritance Traits Studied by Mendel Flower Color In pea plants: The allele for violet flower color (B) is dominant The allele for white flower color (b) is recessive Genotype vs. Phenotype Genotype BB Homozygous dominant Bb Heterozygous bb Homozygous recessive Phenotype A Punnett Square CF - An Autosomal Recessive Trait Carrier mother Punnett Square Carrier father G g G g GG Gg 25% 50% Gg gg 50% 25% Child with CF Independent Assortment • The inheritance pattern of one trait will not affect the inheritance pattern of another • Independent assortment occurs during meiosis • For a single human gamete, the possible ways chromosomes may assort is astounding: 223 = 8,388,608 possible combinations Dihybrid Cross In snapdragons, tallness (T) is dominant to dwarfness(t), while red color is due to gene (R) and white to its corresponding allele (r). The heterozygous condition results in pink (Rr) flower color. A dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. Give the possible genotypes and corresponding phenotypes for all of the possible F1 generation. Step #1: Determine Genotypes of Parents “A dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. “ Dwarf pink = ttRr Homozygous tall, red = TTRR Step #2: Determine Genotypes of Gametes “A dwarf pink snapdragon is crossed with a plant homozygous for tallness and red flowers. “ Dwarf pink = ttRr tR tr tR tr Homozygous tall, red = TTRR TR TR TR TR Step #3: Punnett Square The Punnett square determines the genotypes of the offspring Gametes from TALL red parent TR TR TR TR tR TtRRTtRRTtRRTtRR Gametes from dwarf pink parent tr TtRr TtRrTtRr TtRr tR TtRRTtRRTtRRTtRR tr TtRrTtRr TtRrTtRr Autosomal Recessive: A Pedigree Inheritance of an Autosomal Dominant Trait Incomplete Dominance In snapdragons red flower color is due to gene (R) and white to its corresponding allele (r). The heterozygous (Rr) condition results in pink flower color. This is referred to as “incomplete dominance.” Sex-Linked Traits Traits whose alleles are located on sex chromosomes X-linked traits are traits whose allele is carried on the X chromosome Y-linked traits are traits whose allele is carried on the Y chromosome. Most Y-linked mutations lead to sterility, and can not be inherited. Color Blindness: An X-linked Recessive trait Carrier mother Punnett Square Unaffected father XC XC Xc XCXc XCXc 25% Y XCY 25% 25% XcY 25% Colorblind male A Pedigree - Colorblindness Hemophilia: Another X-linked Recessive trait Carrier mother Punnett Square Unaffected father XH Y XH Xh XHXH XHXh 25% 25% XHY XhY 25% 25% Hemophiliac male Hemophilia in Europe’s Royalty Blood Cell Antigens Blood types are the result of the presence (or absence) of antigens (molecules) on the surface of the individual’s red blood cells. These fall into two groups: A, B, O blood type Rh factor Codominance The gene for antigen A and the gene for antigen B are CODOMINANT. Both traits are expressed completely when the gene for A is inherited from one parent and the gene for B is inherited from the other parent. Bloodtype antigens and antibodies A, B, O Inheritance Allele from Parent 1 Allele from Parent 2 Child’s genotype Child’s phenotype A A AA A A O AO A A B AB AB B A AB AB B B BB B B O BO B O O OO O Rh Inheritance Rh inheritance is independent of A, B, O blood type. Rh factor Rh+ RhParent 1 Rh allele Rh+ RhRh- Possible genotypes Rh+/Rh+ OR Rh+/RhRh-/RhParent 2 Child’s Rh allele phenotype Rh+ Rh+ Rh+ Rh+ RhRh- Chromosomes and DNA DNA has 4 Bases Four DNA Bases Adenine NH2 N NH Guanine O H3C N N NH NH O N NH Thymine Cytosine NH2 NH N O N NH2 NH O The Sugar HO OH O OH Deoxyribose The Nucleotides A O HO NH2 P N N O N O N O HO OH P C HO P N O O OH OH T O G O N O OH O NH2 N N O NH O H3C NH O N NH2 HO P OH O N O OH OH OH O Adenine pairs with Thymine Hydrogen Bonding Guanine pairs with Cytosine Hydrogen Bonding DNA Genes and Base Pairs: A Comparison Genes (estimated) Base Pairs Yeast 6,000 12 million Round Worm 19,000 99 million Mouse 40,000 3 billion Fruit Fly 13,600 165 million Human 40,000 3 billion Species (Saccharomyces cerevisiae) (Caenorhabditis elegans) (Mus musculus) (Drosophila melanogaster) (Homo sapiens) The “Central Dogma” Possible Modes of DNA Replication Replication: 5’ to 3’ Direction ONLY Continuous replication on one strand Discontinuous replication on one strand DNA Replication is Catalyzed by Enzymes DNA Polymerase Adds Complementary Bases DNA Polymerase Sees Errors DNA Polymerase Repairs Errors Four RNA Bases Adenine NH2 N NH Guanine O N NH NH N O N NH Uracil Cytosine NH2 NH N O N NH2 NH O The Sugar HO OH O OH OH Ribose The Nucleotides A O HO P O N N O N O HO N OH N O O O O OH OH O G O P N OH OH HO P NH2 C NH2 N NH O N O OH N NH2 HO P OH O U O NH N O OH OH OH OH OH O The Central Dogma Transcription Transcription is the process by which RNA is built from a template of DNA Transcription Transcription - Initiation - RNA Polymerase Transcription - Elongation Transcription - Termination Editing mRNA Codons in RNA Translation Translation is the process by which protein is made from an mRNA template Codons Why Three Bases per Codon? A one base code: 41 = 4 combinations A two base code: 42 = 16 combinations A three base code: 43 = 64 combinations There are twenty amino acids, so a threebase code is the minimum required. Translation: Initiation Translation: Elongation Translation: Termination Antisense DNA Prevents Translation Definition • A mutation is a change in an organism’s DNA – Silent mutations are changes that do not result in a change to the organisms phenotype – Mutations that occur in germ cells (sperm, eggs) are passed on to offspring – Mutations in somatic (body) cells may be harmless, or may result in disease such as cancer Chromosomal Mutations A Point Mutation Resulting in Nonsense A Point Mutation: An Analogy the red dog bit the tan cat the red mog bit the tan cat This point mutation changes the meaning, resulting in nonsense A Point Mutation Resulting in Missense A Point Mutation: An Analogy the red dog bit the tan cat the red hog bit the tan cat This point mutation changes the meaning, resulting in missense An Insertion Mutation in a Gene An Insertion Mutation: An Analogy the red dog bit the tan cat the red rdo gbi tth eta nca This insertion mutation changes the reading frame A Deletion Mutation in a Gene An Deletion Mutation: An Analogy the red dog bit the tan cat the red ogb itt het anc at_ This deletion mutation changes the reading frame A Frameshift Mutation History of Biotechnology • • • • • • • • • • before 8000 BC – Collecting of seeds for replanting. Evidence that Mesopotamian people used selective breeding (artificial selection) practices to improve livestock. around 7000 BC – Brewing beer, fermenting wine, baking bread with help of yeast. 8000 BC - 3000 BC – Yogurt and cheese made with lactic-acid-producing bacteria by various cultures. 1590 – The microscope is invented by Zacharias Janssen. 1675 – Microorganisms discovered by Anton van Leeuwenhoek. 1856 – Gregor Mendel discovered the laws of inheritance. 1862 – Louis Pasteur discovered the bacterial origin of fermentation. 1919 – Karl Ereky, a Hungarian agricultural engineer, first used the word biotechnology. 1928 – Alexander Fleming noticed that a certain mold could stop the duplication of bacteria, leading to the first antibiotic: penicillin. 1953 – James D. Watson and Francis Crick describe the structure of deoxyribonucleic acid, called DNA for short. History of Biotechnology • • • • • • 1972 – The DNA composition of chimpanzees and gorillas is discovered to be 99% similar to that of humans. 1975 – Method for producing monoclonal antibody developed by Kohler and Milstein. 1980 – – Modern biotech is characterized by recombinant DNA technology. The prokaryote model, E. coli, is used to produce synthetic insulin and other medicine, in human form. (It is estimated that only 5% of diabetics were allergic to animal insulins available before, while new evidence suggests that type 1 diabetes mellitus is caused by an allergy to human insulin). – A viable brewing yeast strain, Saccharomyces cerevisiae 1026, acts as a modifier of the microflora in the rumen of cows and digestive tract of horses). – The United States Supreme Court, in 447 U.S. 303 (1980), rules in favor of microbiologist Ananda Chakrabarty in the case of a USPTO request for a first patent granted to a genetically modified living organism (GMO) in history. 1984 – Nutrigenomics as applied science in animal nutrition. 1994 – U.S. FDA approves of the first GM food: the "Flavr Savr" tomato. 1997 – British scientists, led by Ian Wilmut, from the Roslin Institute report History of Biotechnology • • • • • • 2000 – Completion of a "rough draft" of the human genome in the Human Genome Project. 2002 – Researchers sequence the DNA of rice, the main food source for two-thirds of the world's population. Rice is the first crop to have its genome decoded. 2003 – GloFish, the first biotech pet, hits the North American market. Specially bred to detect water pollutants, the fish glows red under black light thanks to the addition of a natural bioluminescence gene. 2004 – – November – Korean researchers treat spinal cord injury by transplanting multipotent adult stem cells from an umbilical cord blood. – December – A team of researchers at the University of Paris develops a method to produce large number of red blood cells from hematopoietic stem cells, creating an environment that mimics the conditions of bone marrow. 2005 – – January – Researchers at the University of Wisconsin-Madison differentiate human blastocyst stem cells into neural stem cells, and finally into spinal motor neuron cells. Retrieved from "http://en.wikipedia.org/wiki/Timeline_of_biotechnology" Modern Biotechnology some examples • • • • • • • Recombinant DNA Stem cell therapy Cloning Designer drugs Genomics Proteomics Gene Therapy What are the potential benefits? What are the potential dangers? What are the ethical issue? Genetically Modified Bacteria Cloning: An Example Cloning in Agriculture Stem Cells: Another Example Gene Therapy