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10.2 mendelian genetics

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  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12
  • Mendelian Genetics 01/20/12

10.2 mendelian genetics 10.2 mendelian genetics Presentation Transcript

  • Mendelian Genetics Section 10-2 Pages 277-282
  • Gregor Mendel
    • Austrian monk and plant breeder
    • He joined the monastery in 1843
    • He carried out the first important studies of heredity
    • He was the first person to succeed in predicting how
    • traits are transferred from one generation to the next.
    • He published his findings in 1866.
  • Why peas?
    • Can be grown in a small area
    • Produce lots of offspring
    • Produce pure plants when allowed to self-pollinate for several generations
    • Can be artificially cross-pollinated
  • Why Peas?
    • Peas contain both gametes in the same flower
    • Pollen contains sperm produced by the stamen
    • Ovary contains eggs inside the flower
    • Pollen carries sperm to the eggs for fertilization
      • Self-fertilization can occur in the same flower
      • Cross-fertilization can occur between flowers
  • Genetic Terms
    • Heredity – the passing on of characteristics from parents to offspring
    • Genetics – the branch of biology that studies heredity
    • Traits – characteristics that are inherited
    • P 1 generation – “parent” - the original true-breeding parents
    • F 1 generation – “filial” (or son or daughter) offspring of the parent plants
    • F 2 or “second filial generation” (or granddaughter or grandson)
    Mendel’s Experiments- Terms
  • Mendel’s Experiments
    • First Generation (F 1 )
    • Mendel grew seeds from a cross between green-seed and yellow-seed plants. All of the offspring had yellow seeds.
    • Second Generation (F 2 )
    • Mendel allowed the plants in the 1 st generation to self pollinate. ¾ of the plants had yellow seeds and ¼ had green.
    • Ratio of 3:1 (3 yellow to 1 green)
  • Alleles
    • Alleles- alternative form of a single gene passed from generation to generation.
    • Organisms have 2 genes that control each trait. These genes are located on the chromosomes
    • Dominant trait – appears in the F 1 generation
    • Recessive trait – disappears in the F 1 generation
  • A plant could have:
    • 2 alleles for tallness (TT)
    • 2 alleles for shortness (tt)
    • 1 allele for tallness and 1 for shortness (Tt)
    • The 2 alleles are located on different copies of a chromosome – one copy inherited from the female parent and one from the male parent
  • Rule of dominance
    • Pea plants that have at least 1 allele for tallness (TT or Tt) are tall because the allele for tallness is dominant over the allele for shortness
    • The only way a plant can be short is if both height alleles are for a short plant (tt)
    • Homozygous – an organisms 2 alleles for a trait are the same (TT, tt)
    • Heterozygous - an organisms 2 alleles for a trait are different (Tt)
  • Phenotypes & Genotypes
    • 2 organisms can look alike but have different gene combinations
    • Phenotype – the way an organism looks and behaves (tall or short)
    • Genotype – the gene combination an organism contains (TT, Tt, tt)
  • Law of Segregation
    • Law of Segregation- two alleles for each trait separate during meiosis.
    • A TT plant can only produce T gametes
    • A Tt plant can produce both T gametes and t gametes
    • A tt plant can only produce t gametes
    • The 2 alleles come together during fertilization.
  •  
  • TT Tt TT TT Tt Tt Tt TT TT Tt T T T T t t T T segregation segregation fertilization fertilization gametes gametes P F 1 F 2 Segregation of Alleles
  • Mendel’s Crosses
    • Hybrid – offspring of parents that have different traits
    • Mono – means one
    • Di- means two
    • Monohybrid crosses – the two parent plants differ by a single trait (height)
    • Dihybrid cross – parents differ by two traits (height and color)
  • Monohybrid Cross (Seed color) Genotype- 1 YY, 2 Yy, 1yy or 1:2:1 Phenotype- 3 Yellow, 1 Green or 3:1
  • Punnett Squares
    • 1905, Reginald Punnett, an English biologist, devised the shorthand way of finding the expected proportions of possible genotypes in the offspring of a cross
    • Used to predict the possible genotypes of offspring
    • In reality, you don’t get the exact ratio of results shown in the square
  • Punnett Square-Monohybrid Cross
  • Punnett Square T t T TT Tt t Tt tt
    • Trait: Seed Shape
    • Alleles: R – Round r – Wrinkled
    • Cross: Round seeds x Round seeds
    • Rr x Rr
    Monohybrid Cross R r r R RR rr Rr Rr Genotype: RR, Rr, rr Phenotype : Round & wrinkled G.Ratio: 1:2:1 P.Ratio: 3:1
    • Trait: Seed Shape
    • Alleles: R – Round r – Wrinkled
    • Cross: Round seeds x Round seeds
    • RR x Rr
    Monohybrid Cross R R r R RR Rr RR Rr Genotype: RR, Rr Phenotype : Round Genotypic Ratio: 1:1 Phenotypic Ratio: All alike
    • Trait: Seed Shape
    • Alleles: R – Round r – Wrinkled
    • Cross: Wrinkled seeds x Round seeds
    • rr x Rr
    Monohybrid Cross r r r R Rr rr Rr rr Genotype: Rr, rr Phenotype : Round & Wrinkled G. Ratio: 1:1 P.Ratio: 1:1
  • Law of Independent Assortment
    • Alleles for different traits are distributed to sex cells (& offspring) independently of one another.
    • This law can be illustrated using dihybrid crosses .
  • Dihybrid Cross (Seed color and shape) Phenotypes: 9 Round and Yellow 3 Wrinkled and Yellow 3 Round and Green 1 Wrinkled and Green or 9:3:3:1 ratio
  • Punnett Square-Dihybrid Cross
  • Dihybrid Cross
    • Traits: Seed shape & Seed color
    • Alleles: R round r wrinkled Y yellow y green
    RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations
  • Dihybrid Cross RY Ry rY ry RY Ry rY ry
  • Dihybrid Cross RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RY Ry rY ry RY Ry rY ry
  • Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1
  • Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods