General Biology 1004 Chapter 9 Lecture Handout, Summer 2005 Dr. Frisby

Transcription

1 Slide 1 CHAPTER 9 Patterns of Inheritance PowerPoint Lecture Slides for Essential Biology, Second Edition & Essential Biology with Physiology Presentation prepared by Chris C. Romero Neil Campbell, Jane Reece, and Eric Simon Slide 2 BIOLOGY AND SOCIETY: TESTING YOUR BABY Genetic testing Allows expectant parents to test for possibilities in their unborn child Includes amniocentesis and CVS Has risks associated with it Figure 9.1 Slide 3 HERITABLE VARIATION AND PATTERNS OF INHERITANCE Wild type traits are traits most commonly found in nature Figure 9.2

2 Slide 4 Various traits exist in organisms Slide 5 Parents: Parents: Wild-type Wild-type Wild-type Sky-blue Offspring: All Wild-type Firstgeneration offspring: All wild-type Matings (a) Offspring from the mating of two wild-type birds Secondgeneration offspring: 3 / 4 and 1 / 4 Wild-type Sky-blue (b) Two generations of offspring from the mating of a wild-type with a sky-blue bird Figure 9.3 Slide 6 Gregor Mendel Figure 9.4

3 Slide 7 In an Abbey Garden Mendel studied garden peas Stamen Carpel Figure 9.5 Slide 8 1 Removed stamens from purple flower White Mendel carried out some crossfertilization Parents (P) Carpel Purple 3 2 Transferred pollen from stamens of white flower to carpel of purple flower Stamens Pollinated carpel matured into pod 4 Planted seeds from pod Offspring (F 1 ) Figure 9.6 Slide 9 He also created true-breeding varieties of plants Mendel then crossed two different truebreeding varieties, creating hybrids

4 Slide 10 Mendel s Principles of Segregation Mendel performed many experiments Slide 11 Dominant Recessive Dominant Recessive Flower color Purple White Pod shape Inflated Constricted Pod Color Green Yellow Flower position Axial Terminal Seed color Yellow Green Stem length Tall Dwarf Seed shape Round Wrinkled Figure 9.7 Slide 12 Monohybrid Crosses A monohybrid cross is a cross between parent plants that differ in only one characteristic P Generation (true-breeding parents) F 1 Generation Purple flowers White flowers All plants have purple flowers Fertilization among F 1 plants (F 1 F 1) F 2 Generation 3 / 4 of plants have purple flowers 1 / 4 of plants have white flowers (a) Mendel s crosses tracking one characteristic (flower color) Figure 9.8a

5 Slide 13 Mendel developed four hypotheses from the monohybrid cross Slide 14 An explanation of Mendel s results, including a Punnett square Genetic makeup (alleles) P plants PP pp Gametes All P All p F 1 plants: (hybrids) All Pp Gametes 1 / 2 P 1 / 2 p F 2 plants: Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp Eggs p P Pp PP pp P Pp Sperm p (b) Explanation of the results in part (a) Figure 9.8b Slide 15 Phenotype Genotype

6 Slide 16 Mendel s principle of segregation Slide 17 Genetic Alleles and Homologous Chromosomes Homologous chromosomes Slide 18 Homologous chromosomes: Gene loci P a B Dominant allele Genotype: P a b PP aa Bb Recessive allele Homozygous for the dominant allele Homozygous for the recessive allele Heterozygous Figure 9.9

7 Slide 19 Homozygous Heterozygous Slide 20 Mendel s Principle of Independent Assortment Two hypotheses for gene assortment in a dihybrid cross Slide 21 (a) Hypothesis: Dependent assortment (b) Hypothesis: Independent Assortment P Generation RRYY rryy RRYY rryy Gametes RY ry Gametes RY ry F 1 Generation RrYy RrYy Eggs 1 / 2 RY 1 / 2 RY Sperm 1 1 / RY / Eggs 4 RY 4 Sperm 1 1 ry / ry / 4 4 RRYY 1 / ry 1 2 / 2 ry 1 / 4 Ry RrYY RrYY 1 / 4 Ry F 2 Generation 1/ 4 ry RRYy rryy RRYy 1 / 4 ry RrYy RrYy RrYy RrYy 9 / 16 Yellow round Actual results contradict hypothesis rryy RRyy rryy Rryy Rryy rryy Actual results support hypothesis 3 / 16 Green round 3/ 16 Yellow wrinkled 1 / 16 Green wrinkled Figure 9.10

8 1 / 4 1 / 2 1 / 4 General Biology 1004 Chapter 9 Lecture Handout, Summer 2005 Slide 22 Mendel s principle of independent assortment Blin d Blin d Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind(pra) B_nn Chocolate coat, normal vision bbn_ Chocolate coat, blind (PRA) bbnn (a) Mating of heterozygotes (black, normal vision) BbNn BbNn Phenotypic ratio of offspring (b) 9 black coat, normal vision 3 black coat, blind (PRA) 3 chocolate coat, 1 chocolate coat, normal vision blind (PRA) Figure 9.11 Slide 23 Using a Testcross to Determine an Unknown Genotype A testcross is a mating between Testcross: Genotypes P_ pp Two possibilities for the purple flower: PP Pp Gametes P P p P Pp p Pp pp Offspring All purple 1 purple : 1 white Figure 9.12 Slide 24 The Rules of Probability The rule of multiplication F 1 Genotypes B b female Formation of eggs B b male Formation of sperm 1/ 2 B B 1/ 2 b b B B B 1 / 4 ( 1 / 2 1 / 2) B b 1 / 2 b b b F 2 Genotypes 1/ 4 Figure 9.13

9 Slide 25 Family Pedigrees Mendel s principles apply to the inheritance of many human traits Dominant Traits Recessive Traits Freckles No freckles Widow s peak Straight hairline Free earlobe Attached earlobe Figure 9.14 Slide 26 A family pedigree Female Male Dd Joshua Lambert Dd Abigail Linnell D_ John Eddy D_ Hepzibah Daggett Deaf Hearing D_ Abigail Lambert dd Jonathan Lambert Dd Elizabeth Eddy Dd Dd dd Dd Dd Dd dd Figure 9.15 Slide 27 Human Disorders Controlled by a Single Gene Many human traits

10 Slide 28 Table 9.1 Slide 29 Recessive Disorders Most human genetic disorders are recessive Parents: Normal Dd Normal Dd Offspring: Eggs d D Dd Normal (carrier) DD Normal D Dd Normal (carrier) Sperm d dd Deaf Figure 9.16 Slide 30 Dominant Disorders Some human genetic disorders are dominant Figure 9.17

11 Slide 31 BEYOND MENDEL Some patterns of genetic inheritance are not explained by Mendel s principles Slide 32 Incomplete Dominance in Plants and People In incomplete dominance F 1 hybrids have an appearance in between the phenotypes of the two parents In the F2, the genotypic ratio and phenotypic ratio are the same P Generation Red RR F 1 Generation F 2 Generation Gametes R r Gametes 1 / 2 R 1 / 2 r Pink Rr White rr Eggs 1 / 2 R 1 / 2 R Sperm Red 1 r 1 / RR / 2 2 r Pink Pink Rr rr White rr Figure 9.18 Slide 33 Hypercholesterolemia LDL (carries cholesterol) LDL receptor (mops up LDL) Cell Normal Genotypes: HH Homozygous for ability to make LDL receptors Mild disease Hh Heterozygous Severe disease hh Homozygous for inability to make LDL receptors Figure 9.19

12 Slide 34 Multiple Alleles and Blood Type The ABO blood groups in humans are examples of multiple alleles Figure 9.20 Slide 35 Two of the human blood type alleles exhibit codominance Slide 36 Pleiotropy and Sickle-Cell Disease Pleiotropy is the impact of a single gene on more than one characteristic

13 Slide 37 Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickled cells Breakdown of red blood cells Clumping of cells and clogging of small blood vessels Accumulation of sickledcells in spleen Physical weakness Anemia Heart failure Pain and Brain fever damage Damage to other organs Spleen damage Impaired mental function Paralysis Pneumonia and other infections Rheumatism Kidney failure Figure 9.21 Slide 38 Polygenic Inheritance Polygenic inheritance is the additive effects of two or more genes on a single phenotype P Generation F 1 Generation F 2 Generation aabbcc (very light) Eggs AaBbCc AABBCC (very dark) AaBbCc Sperm Figure 9.22 Slide 39 The Role of Environment Many human characteristics result from a combination of heredity and environment

14 Slide 40 THE CHROMOSOMAL BASIS OF INHERITANCE The chromosome theory of inheritance states that Slide 41 P Generation Yellow -round seeds (YYRR) Green -wrinkled seeds (yyrr ) Meio sis Gametes Fertilization F 1 Generation Principle of Segregation: Follo w the long chromosomes (carrying R and r) taking either the left or right branch. Meio sis All round yellow seeds (RrYy) Principle of Independent Assortment: Follow both the long and the short chromosomes. T he R and r alleles segregate in anaphase I of meiosis. Metaphase I (alternative arrangements) They are arranged in either of two equally likely ways at metaphase I. Only one long chromosome ends up in each gamete. Metaphase II They assort independently, giving four gamete types. Gametes Fertilization recombines the r and R alleles at random. F 2 Generation Fertilization among the F 1 plants Fertiliz ation results in the 9:3:3:1 phenotypic ratio in the F 2 generation. Figure 9.23 Slide 42 Gene Linkage In 1908, British biologists discovered an inheritance pattern inconsistent with Mendelian principles (a) Experiment: Purple flower PpLl PpLl Long Pollen Figure 9.24a

15 Slide 43 This inheritance pattern was later explained by linked genes, which are (b) Explanation: Linked genes Parental diploid cell PpLl Most gametes Meiosis Fertilization Egg Sperm Most offspring 3 purple long : 1 red round Not accounted for: purple round and red long Figure 9.24b Slide 44 Genetic Recombination: Crossing Over and Linkage Maps Two linked genes Slide 45 (c) Explanation: Crossing over Tetrad Crossing over Parental-type gametes Tetrad Fertilization Purple round Red long Among the offspring, some with recombinant phenotypes Figure 9.24c

16 Slide 46 Early studies of crossing over were performed using the fruit fly Drosophila melanogaster Wild type (gray body, long wings, red eyes) Variant (black body, short wings, cinnabar eyes) Figure 9.25 Slide 47 Studies using Drosophila Chromosome g c l 17% 9% 9.5% Recombination frequencies Figure 9.26 Slide 48 SEX CHROMOSOMES AND SEX -LINKED GENES Sex chromosomes

17 Slide 49 Sex Determination in Human and Fruit Flies Sex chromosomes Male 44 + XY Somatic cells Female 44 + XX 22 + X 22 + Y 22 + X Sperm Egg 44 + XX Female 44 + XY Male Figure 9.27 Slide 50 Sex-Linked Genes Sex-linked genes (a) (b) Figure 9.28 Slide 51 Inheritance patterns of a sex-linked gene Female X RXR Male X ry Female X R X r Male X R Y Female X R X r Male X ry All females inherit two X chromosomes, one from each parent. All males inherit one X chromosome, always from the mother. R = red -eye allele r = white -eye allele Female Male Female Male (a) Homozygous red-eyed female whiteeyed male (b) Heterozygous female red - eyed male (c) Heterozygous female whiteeyed male Figure 9.29

18 Slide 52 Sex-Linked Disorders in Humans A number of human conditions result from sexlinked (X-linked) genes Slide 53 Red-green color blindness Figure 9.30 Slide 54 Hemophilia Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Alexis Figure 9.31

19 Slide 55 Duchenne muscular dystrophy Slide 56 EVOLUTION CONNECTION: THE TELLTALE Y CHROMOSOME Sex chromosomes Slide 57 The Y chromosome of human males is only about one-third the size of the X chromosome Scientists believe that X and Y were once a fully homologous pair Major episodes of change have rearranged pieces of the Y chromosome

20 Slide 58 Because the Y is passed more or less intact, researchers recently used comparisons of Y DNA to confirm that the Lemba tribe in Africa descended from ancient Jews Figure 9.32 Chapter 9 Study Objectives 1. Describe the processes and risks associated with amniocentesis and chorionic villus sampling (CVS). Describe the circumstances in which these tests are best used and the possible consequences if these fetal tests reveal a genetic disorder. 2. Define and distinguish between self-fertilization, cross-fertilization, true-breeding organisms, hybrids, the P generation, the F 1 generation, and F 2 generation. 3. Define and distinguish between the following pairs of terms: dominant allele versus recessive allele, genotype versus phenotype, and heterozygous versus homozygous. 4. Define Mendel s principle of independent assortment, and explain how it applies to a dihybrid cross. 5. Explain how a testcross is performed to determine the genotype of an organism. 6. Explain how and when the rule of multiplication should be used to determine the probability of an event. 7. Explain how a pedigree is used to determine how a particular human trait is inherited. Define a carrier, and explain how carriers are revealed in human pedigrees. 8. Compare the frequency and method of inheritance of recessive and dominant disorders. 9. Define and distinguish between complete dominance, incomplete dominance and codominance. 10. Explain why people who are heterozygous for sickle-cell disease are resistant to malaria. 11. Define and distinguish between pleiotropy and polygenic inheritance. 12. Explain how the environment influences the expression of traits. 13. Define the chromosome theory of inheritance, and explain how linked genes are inherited differently from other nonlinked genes. 14. Explain why researchers used fruit flies and how they created linkage maps. 15. Explain how chromosomes determine the sex of a human. 16. Explain why sex-linked diseases are more common in human males. 17. Describe the general characteristics of the following sex-linked disorders in humans: redgreen color blindness, hemophilia, and Duchenne muscular dystrophy. 18. Explain how Y chromosomes can be used to trace the ancestry of humans.