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Biotech History

Biotech History. Chapter 3. Mendel’s principle of segregation describes the inheritance of a single characteristic. P GENERATION (true-breeding parents). From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic

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Biotech History

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  1. Biotech History Chapter 3

  2. Mendel’s principle of segregation describes the inheritance of a single characteristic P GENERATION(true-breedingparents) • From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic • One characteristic comes from each parent Purple flowers White flowers All plants have purple flowers F1generation Fertilization among F1 plants(F1 x F1) F2generation 3/4 of plantshave purple flowers 1/4 of plantshave white flowers

  3. GENETIC MAKEUP (ALLELES) • A sperm or egg carries only one allele of each pair P PLANTS PP pp Gametes All P All p • The pairs of alleles separate when gametes form • This process describes Mendel’s law of segregation • Alleles can be dominant or recessive F1 PLANTS(hybrids) All Pp Gametes 1/2P 1/2p P P Eggs Sperm PP F2 PLANTS p p Pp Pp Phenotypic ratio3 purple : 1 white pp Genotypic ratio1 PP : 2 Pp : 1 pp

  4. The principle of independent assortment is revealed by tracking two characteristics at once • By looking at two characteristics at once, Mendel found that the alleles of a pair segregate independently of other allele pairs during gamete formation • This is known as the principle of independent assortment

  5. HYPOTHESIS: DEPENDENT ASSORTMENT HYPOTHESIS: INDEPENDENT ASSORTMENT RRYY rryy PGENERATION RRYY rryy ry ry Gametes RY Gametes RY F1GENERATION RrYy RrYy Eggs 1/2 RY 1/2 RY Sperm Eggs 1/4 RY 1/4 RY 1/2 ry 1/2 ry 1/4 rY 1/4 rY RRYY 1/4 Ry 1/4 Ry RrYY RrYY F2GENERATION 1/4 ry 1/4 ry RRYy rrYY RrYy Yellow round RrYy RrYy RrYy RrYy 9/16 Actual resultscontradict hypothesis Green round rrYy RRyy rrYy 3/16 ACTUAL RESULTSSUPPORT HYPOTHESIS Yellow wrinkled Rryy Rryy 3/16 Yellow wrinkled rryy 1/16

  6. Independent assortment of two genes in the Labrador retriever Blind Blind Black coat, normal visionB_N_ Black coat, blind (PRA)B_nn Chocolate coat, normal visionbbN_ Chocolate coat, blind (PRA)bbnn PHENOTYPES GENOTYPES MATING OF HETEROZYOTES(black, normal vision) BbNn BbNn 9 black coat,normal vision 3 black coat,blind (PRA) 3 chocolate coat,normal vision 1 chocolate coat,blind (PRA) PHENOTYPIC RATIO OF OFFSPRING

  7. Homologous chromosomes bear the two alleles for each characteristic • Alternative forms of a gene (alleles) reside at the same locus on homologous chromosomes GENE LOCI DOMINANT allele P a B P a b RECESSIVE allele GENOTYPE: PP aa Bb HOMOZYGOUSfor thedominant allele HOMOZYGOUSfor therecessive allele HETEROZYGOUS

  8. Mendel’s principles reflect the rules of probability • Inheritance follows the rules of probability • The rule of multiplication and the rule of addition can be used to determine the probability of certain events occurring F1 GENOTYPES Bb female Bb male Formation of eggs Formation of sperm 1/2 B B 1/2 B B 1/2 b b 1/2 1/4 B b b B 1/4 1/4 b b F2 GENOTYPES 1/4

  9. No One Was Impressed! Not even Darwin…..

  10. But in the early 1900’s Walter Sutton, Reginald Punnett, Thomas Hunt Morgan and others rediscovered Mendel’s work!

  11. THE CHROMOSOMAL BASIS OF INHERITANCE Chromosome behavior accounts for Mendel’s principles • Genes are located within chromosomes • Their behavior during meiosis accounts for inheritance patterns

  12. Crossing over produces new combinations of alleles • This produces gametes with recombinant chromosomes • The fruit fly Drosophila melanogaster was used in the first experiments to demonstrate the effects of crossing over

  13. A B a b B A a b A b a B Tetrad Crossing over Gametes

  14. Geneticists use crossover data to map genes • Crossing over is more likely to occur between genes that are farther apart • Recombination frequencies can be used to map the relative positions of genes on chromosomes Chromosome g c l 17% 9% 9.5%

  15. A partial genetic map of a fruit fly chromosome Mutant phenotypes Shortaristae Black body (g) Cinnabar eyes (c) Vestigial wings (l) Browneyes Long aristae(appendageson head) Gray body (G) Red eyes (C) Normal wings (L) Redeyes Wild-type phenotypes

  16. SEX CHROMOSOMES AND SEX-LINKED GENES Chromosomes determine sex in many species • A human male has one X chromosome and one Y chromosome • A human female has two X chromosomes • Whether a sperm cell has an X or Y chromosome determines the sex of the offspring

  17. Sex-linked genes exhibit a unique pattern of inheritance • All genes on the sex chromosomes are said to be sex-linked • In many organisms, the X chromosome carries many genes unrelated to sex • Fruit fly eye color is a sex-linked characteristic

  18. The Experiments of Griffith and Avery What is this “stuff” that transforms the next generation?

  19. Griffith’s Experiment

  20. The Work of Hershey and Chase DNA or Proteins?

  21. Early experiments Miescher, Levene, etc.

  22. Miescher found great quantities of white blood cells in bandages from a nearby hospital clinic.Pus washed off the bandages contained numerous amounts of white blood cells.

  23. Mendel Darwin Walter Sutton Morgan Miescher Levene Griffith Avery Hershey Chase Pauling Chargaff Wilkins Franklin On The Shoulders of Scientists

  24. Enter Watson and Crick and the Central Dogma DNA-RNA-Protein But is it entirely true….Just like Mendel’s Laws, there are exceptions!

  25. Exceptions • Introns and exons • Junk DNA?? No Way! • Reverse Transcriptase • Transposons • RNA is not just a ‘middleman’

  26. Misunderstandings about Genes • Genes make proteins • Genes are on chromosomes • Genes replicate themselves • DNA is like a blueprint • Genes determine who we are

  27. Understanding Evolution • Genetic variation-recombination and mutation • Selection Pressure-natural selection, environment

  28. Types of Mutations • Macromutations-chromosomal-deletions, duplications, translocations, inversions • Micromutations-point, frameshift

  29. Recombination • Sexual reproduction • Meiosis • Conjugation • Transformation • Transduction

  30. Asexual Organisms • Cloning-binary fission • Conjugation-bacteria sex • Transduction-viruses • Transformation-picking up DNA from surroundings

  31. Variation, Chance, Change • Mutation, Recombination • Environmental ‘Chance and Change’ Selection

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