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MENDELIAN GENETICS

MENDELIAN GENETICS. OBJECTIVES. Understand Mendel’s principles governing genetics Understand meaning of relevant vocabulary Predict results of mono/dihybrid crosses using Punnett square Know exceptions to rules . GENETICS. Genetics: Heredity:. Gene (Character): Locus (loci= pl.):

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MENDELIAN GENETICS

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  1. MENDELIAN GENETICS

  2. OBJECTIVES • Understand Mendel’s principles governing genetics • Understand meaning of relevant vocabulary • Predict results of mono/dihybrid crosses using Punnett square • Know exceptions to rules

  3. GENETICS • Genetics: • Heredity:

  4. Gene (Character): Locus (loci= pl.): Allele (Trait): Genotype: Phenotype: GENETICS TERMINOLOGY

  5. MENDEL • Gregor Mendel • Interested in basic patterns governing the transmission of traits from parent to offspring • Mendel’s work precedes an understanding of meiosis/genes/chromosomes

  6. HISTORICAL HYPOTHESES REGARDING INHERITANCE Blending Inheritance Hypothesis: Inheritance of Acquired Characteristics Hypothesis

  7. MENDEL • Mendel performed crosses between pure bred garden peas • Began studying inheritance of ONE trait • Later, multiple traits studied together

  8. MENDEL’S CROSSES • Mendel's plants had twoobservable“forms” (alleles) of each “character” (gene) • Green or Yellow seeds • Round or Wrinkled seeds

  9. Forms of Trait (Phenotype) Trait or Seed shape Round Wrinkled Round Wrinkled or Seed color Green Yellow Yellow Green Pod shape or Constructed Inflated Smooth Constricted or Pod color Yellow Green Green Yellow

  10. Trait Forms of Trait (Phenotype) Flower color or Purple White White Purple Flower and pod position or Axial (on stem) Terminal (at tip) Axial (on stem) Terminal (at tip) Stem length or Dwarf Tall Tall Dwarf

  11. MENDEL • Looked at traits exhibited by progeny of crosses • Found observableevidence of how parents transmit traits to offspring

  12. MENDEL’S PEA PLANTS • Pisum sativum

  13. Male parts = anthers • Pollen grain contain sperm • Female parts = pistil • Ovule = eggs SELF FERTILIZATION Stigma (receives pollen) Anthers (produce pollen grains, which contain male gametes) Ovules (produce female gametes)

  14. MENDEL’S PEA PLANTS Controlled Mating: • Cut off reproductive organ to stop self fertilization • Cross fertilize plants in a controlled fashion • Plant that contributes pollen • Plant that receives the pollen

  15. CROSS-POLLINATION 1. Remove anthers from one plant. 2. Collect pollen from a different plant. 3. Transfer pollen to stigma of the 1st plant (plant without anthers)

  16. MENDEL’S CROSSES Round Parent x WrinkledParent

  17. MENDEL’S CROSSES Round x Round (F1) Next, Mendel crossed F1 (bro-sis mating):

  18. MENDEL’S CROSSES Mendel Determines (Phenotypic) Ratio: F2: 5474 Round : 1850 Wrinkled • Similar pattern observed in other 6 traits

  19. MENDEL’S CONCLUSIONS

  20. MENDEL’S SYMBOLS • Mendel assigned symbols to hereditary characters • Letters represent versions of a gene (alleles): • Ex: If Letter “r” represents a gene then:

  21. PUNNETT SQUARE • R.C. Punnett • Leading geneticist in early 1900s • Invented technique called the “Punnett Square” • Place gamete possibilities for 2 parents along axes • Internal boxes represent union of gametes • Used to predict genotype and phenotype of potential zygote

  22. MENDEL’S CROSS OF PURE LINE PEA PLANTS PARENT: R R R is round r is wrinkled PARENT: r r ** hint: gametes along top, “whole people” on inside

  23. MENDEL’S CROSS OF F1 PLANTS Crossing the F1s: Rr x Rr R = round r = wrinkled • Phenotypic Ratio: • Genotypic Ratio

  24. Three possible genotypes for each gene in a diploid cell: Homozygous: Homozygous Dominant: Homozygous Recessive: Heterozygous: POSSIBLE GENOTYPES

  25. PROBABILITY THEORY In Diploid Organisms, • Each allele has 50% chance of being found in a particular gamete • To calculate likelihood of two alleles combining (i.e. fertilization):

  26. MENDEL’S CROSSES • Dihybrid Crosses: • Mendel used pea plants to follow inheritance of TWOtraits • Another pattern began to emerge…

  27. MENDEL’S SYMBOLS • Seed Shape: • R is dominant allele (Round) • r is recessive allele (Wrinkled) • Seed Color: • Y is dominant allele (Yellow) • y is recessive allele (Green)

  28. F2 OFFSPRING FROM DIHYBRID CROSS F2 generation phenotype Mendel’s Numbers 315 101 108 32 = 556 Fraction of progeny 9/16 3/16 3/16 1/16 = 1 Note: New mixtures of traits are observed in F2!!

  29. PUNNETT SQUARE FOR TWO TRAITS Do genes segregate into gametes together or independently?

  30. PUNNETT SQUARE FOR TWO TRAITS If genes segregate independently of each other, we end up with

  31. MENDEL’S LAW OF INDEPENDENT ASSORTMENT • Law of Independent Assortment:

  32. INDEPENDENT ASSORTMENT During meiosis I, homologs can line up two different ways before separating. Brown eyes Blue eyes OR Black hair Red hair

  33. THE TEST CROSS • To determine genotype of an individual

  34. MENDEL Why Mendel Was Successful: • Unbiased • Selected good model organism • Used pure breeds as parents • Large sample size • Quantitative analysis • Controlled experiments • Studied obvious traits

  35. CONCLUSIONS: MENDELIAN GENETICS

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