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HEREDITY “The Code of Life” 1 What is Genetics? (Chapter 1) • Genetics is the study of heredity • Genetics is the study of how traits are passed from an organism to its offspring 2 Genetics Genetics helps to explain why living organisms: • Resemble their parents • Each have unique characteristics from any other living organism 3 History of Genetics Began with Gregor Mendel • in mid-1800’s • working with pea plants – looking for a pattern in the way certain characteristics (or traits) are handed down from one generation to the next. 4 Pea Plants Why were pea plants chosen? 1. Grow and reproduce quickly 2. Have a variety of characteristics (or traits) 3. Many traits (list) could be studied in one experiment 4. Can be crossed, or bred, easily 5 Reproductive Structures of Flowers • Stamen = Male Sex Structure (pollen) • Pistil = Female Sex Structure (seeds) 6 Self-Pollination Pollen from the stamen (male) of one flower lands on the pistil (female) of the same flower, or a different flower on the same plant. Since only one plant has been involved , it has pollinated itself. 7 Cross-Pollination Pollen from the stamen (male) of one flower lands on the pistil (female) of the flower of a different plant. The pollen has crossed between two plants, hence cross-pollination. 8 Self-Pollination (Pure Tall x Pure Tall) Parents F1 Generation X Tall (TT) Purebred = Tall (TT) Tall (TT) Tall (TT) Tall (TT) Tall (TT) Purebred 9 Self-Pollination (Pure Short x Pure Short) Parents X Short tt Purebred F1 Generation = Short tt Short tt Short Short tt tt Short tt Purebred 10 Cross-Pollination (Pure Tall x Pure Short) F1 Generation Parents X Tall TT Purebred = Short tt Tall Tt Tall Tt Tall Tt Tall Tt Hybrids 11 Cross-Pollination (Hybrid Tall x Hybrid Tall) F2 Generation F1 Generation X Tall Tt Hybrids = Tall Tt Tall TT Purebred Tall Tt Tall Tt Hybrids Short tt Purebred 12 “Father of Genetics” • Gregor Mendel became known as the “Father of Genetics”. • He identified these traits as “characters” which we now call genes. • Genes are the units of heredity. • Genetics is the study of heredity, or the passing of traits from an organism to its offspring. 13 Dominant and Recessive • Dominant means “STRONG” • Recessive means “weak” • Mendel found that some traits were stronger (dominant) while others were weaker (recessive). • Generally, letters are used to represent the gene – Capital letter is used for the Dominant gene – Small letter is used for the Recessive gene 14 Purebred vs. Hybrid • Purebred: If genes are alike for a particular trait – Example: YY or yy • Hybrid: If genes are different for a trait – Example: Yy – NOTE: Hybrids are produced by crossing two purebred organisms with opposite traits 15 Mendel’s Hypothesis • Mendel made a hypothesis (suggested explanation) for the way traits were passed to the next generation – Each trait must have a pair of factors, or genes, for each trait – Each plant in next generation also had a pair of genes for each trait, so must have received one from each parent. 16 The Law of Segregation • During the creation of the sex cells (sperm for the male, eggs for the female), the parent’s gene pairs must segregate (or separate). This is the Law of Segregation. • Sex cells carry half the gene pair for the new generation. So that after fertilization (union of sperm and egg), the new individual has the completed pair of genes. 17 Law of Segregation Yy Y Parent y Sex cell 18 Law of Independent Assortment • This law states the each gene pair for a trait is inherited independently of the gene pairs for all other traits. Yy Y Tt y T Rr t R Ss r S s 19 Incomplete Dominance • Sometimes, in the gene pairs, neither gene is dominant nor recessive. Neither gene has the ability to mask (hide) the other. As a result, the traits carried by the two genes appear to be blended. This is Incomplete Dominance. X RR (red) = WW (white) RW (pink) 20 Six Genetic Principles 1. Traits, or characteristics, are passed on from one generation of organisms to the next generation. 2. The traits of an organism are controlled by genes. 3. Organisms inherit genes in pairs, one gene from each parent. 21 Six Genetic Principles (continued) 4. Some genes are dominant, whereas other genes are recessive. 5. Dominant genes hide recessive genes when both are inherited by an organism. 6. Some genes are neither dominant nor recessive. These genes show incomplete dominance. 22 Genetics and Probability • Probability is the possibility, or likelihood, that a particular event will occur. • Probability won’t tell us what WILL happen, BUT… • Probability can be used to predict the results of genetic crosses. • A probability is usually written as a fraction or a percentage. 23 Punnett Squares • In addition to probability, a special chart called a Punnett square is used to show the possible gene combinations in a cross between two organisms. • The chart was developed by Reginald C. Punnett, an English geneticist. 24 Phenotype and Genotype • The Phenotype refers to the physical appearance of an organism. • The Genotype is the actual gene makeup of the organism. 25 Phenotype and Genotypes Parents Black White X BB (Purebred) F1 Generation Black Black Bb Hybrid Bb Hybrid bb (Purebred) Black Black Bb Hybrid Bb Hybrid 26 Phenotype and Genotypes (continued) F1 Generation Black Black X Bb (Hybrid) F2 Generation Black Black BB Purebred Bb Hybrid Bb Black Bb Hybrid (Hybrid) White bb Purebred 27 Pea Plant Characteristics (or Traits) • • • • • • • Tall vs. Short (T and t) Round Seeds vs. Wrinkled Seeds (R and r) Yellow Seeds vs. Green Seeds (Y and y) Colored Seed Coat vs. White Seed Coat (C and c) Full Pod vs. Pinched Pod (F and f) Green Pod vs. Yellow Pod (G and g) Side Flowers vs. End Flowers (S and s) 28 •(return) Human Traits 1. Earlobes 2. Hairline Shape 3. Hair 4. Chin 5. Tongue Rolling 6. Dimples 7. Hand Clasping 8. Handedness 9. Freckles 10. PTC Tasting 11. Colorblindness Free Widow’s peak Curly Cleft Can Present L over R Right Present Taste Normal Attached Straight Straight Smooth Can not Absent R over L Left Absent None Colorblind 29 Sample Punnett Square Problems: 1. Determine the genotype and phenotype of each offspring. Find the probability in percent (%). a. Heterozygous large beaks (B-large beak; b-small beak) a. AA x Bi ( Blood Type A, B , O (i)) a. XY x XX (Female-XX; Male-XY) a. Female carrier of colorblindness x male normal vision (c- colorblindness) 30 Quick Lab 1. Go to Pearson: Biology eTextbook. 2. Do the quick lab: How are dimples inherited? on page 315. 31 Pedigree Symbols 32 Pedigree • A table or chart recording a line of ancestors, either of persons or of animals. 33 Mutations • Heritable changes in genetic mutations • Gene mutation = involve changes in one or a few nucleotides (point mutations) – a. substitution= one base is changed to a different base. Affect no more than a single amino acid and sometimes no effect at all. – b. insertion= one base is inserted – c. deletion= one base is removed 34 35 Chromosomal Mutations=involve changes in the number or structure of chromosomes – – – – a. Deletion b. Duplication c. Inversion d. Translocation 36 37 Environmental Factors • Radiation • Mutagens/carcinogens • Harmful chemicals 38 Genetic Mutations 1. Heterochromia 1. Distichiasis 39 3. Red Hair 4. Blue Eyes 5. Freckles 6. Cleft Chin 40 1. Sickle Cell Anemia Detection: Blood Screening Amniocentesis 1. CCR 532 41 Genetic Disease and Disorders • Phenylketonuria (PKU) *absence of enzyme to metabolize amino acid *leads to mental retardation • Detection : Urine Analysis 42 Tay-sach’s Disease *lack of enzyme to break down lipid in the brain •Detection: Blood screening and amniocentesis 43 Hemophilia *rare bleeding disorder that prevents the blood from clotting 44 Cystic Fibrosis • A genetic disorder characterized by the buildup of thick and sticky mucus that can damage many of the major body organs. 45 Down Syndrome • Addition of chromosome in the 21st pair of chromosomes • Detection:Karyotyping = a test to examine chromosomes in a sample of cells. 46 Additional Links • http://www.brooklyn.cuny.edu/bc/ahp/MGInv/MGI.Intro.html • http://anthro.palomar.edu/mendel/mendel_1.htm • http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/GP/Definition.html • • http://nces.ed.gov/nceskids/probability/ http://nces.ed.gov/nceskids/Games.asp 47