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Mendel 2

Mendel 2






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    Mendel 2 Mendel 2 Presentation Transcript

    • More of Mendel pp. 270 - 274
    • What we know…
      • Inheritance of biological characteristics is determined by genes
      • Principle of Dominance
        • When there are two or more alleles for a gene, some are dominant while others are recessive
      • Law of Segregation
        • In sexually reproducing organisms, adult cells have two copies of each gene—one from each parent; these genes segregate when GAMETES are formed
    • Does the segregation of 1 pair of alleles affect the segregation of another pair of alleles?
      • Make a test cross of:
        • True breeding Round Yellow Peas
          • Genotype (RRYY)
        • True breeding Wrinkled Green peas
          • Genotype (rryy)
      RY RY RY RY ry ry ry ry
      • What is the phenotype of the F1 offspring?
      • What is the genotype of the F1 offspring?
    • What this first cross told us…
      • All F1 offspring were heterozygous for seed shape (round) and seed color (yellow) RrYy
      • The F1 plant was made from fusing a gamete carrying RY and a gamete carrying ry
      • Will the dominant alleles stay together or separate when making the F2 offspring?
    • Now cross these hybrid (RrYy) plants on a new 4X4 Punnett Square
    • What does the F2 cross tell us?
      • Are there combinations of alleles that we did not see in either of the parents?
      • This means that the alleles for seed color separated separately than the alleles for seed shape
      • Genes that segregate separately do NOT influence each other’s inheritance
    • Principle of Independent Assortment
      • Genes for different traits can segregate independently during the formation of gametes. This principle helps account for many genetic variations in plants, animals and other organisms.
    • Mendel’s 4 Principle’s
      • Inheritance of biological characteristics is determined by genes
      • Principle of Dominance
      • Law of Segregation
      • Principle of Independent Assortment
    • Exceptions to Mendel
      • Genetics more complicated
      • Some alleles are neither dominant nor recessive
      • Many traits are controlled by multiple alleles or multiple genes
    • Incomplete Dominance
      • When red flowered (RR) plants were crossed with white flowered (WW) plants they made…pink flowers (RW)
      • Which allele is dominant?
        • neither
      • Incomplete dominance:
        • Case in which one allele is not dominant over another
        • The heterozygous phenotype is somewhere between the two homozygous phenotypes
    • Codominance
      • Both alleles contribute to the phenotype
      • Chickens
        • Allele for black feathers is codominant with allele for white feathers
        • Chicken looks speckled with black and white feathers
        • Not like the blending of dominant phenotypes…
        • BOTH dominant phenotypes show up
      • In humans
        • Gene for protein that controls cholesterol levels in the blood
        • People with heterozygous form make both types of protien
    • Multiple Alleles
      • When a gene has more than two alleles
      • NOT more than 2 alleles for a person but MORE than 2 alleles for the trait exist
      • Coat color in rabbits
        • A single gene for coat color
        • At least 4 different alleles
        • Simple dominance and make 4 possible coat colors
      • Genes for human blood type
    • Polygenic Traits
      • “ Poly” many
      • “ -genic” genes
      • Traits controlled by two or more genes
      • Several genes interact to produce a trait
      • Wide range of phenotypes
      • Skin color
        • Four different genes
      • Fruit Fly eye color
        • Three genes make the reddish brown pigment
    • Applying Mendel’s Principles…
      • Apply Mendel’s Principles to many organisms, including humans
      • Thomas Hunt Morgan (1900’s)
        • American geneticist
        • Common fruit fly
          • Drosophilia melanogaster
          • Produced offspring very quickly
          • Single pair of flies=100 offspring
      • Mendel’s principle’s were tested with Drosophilia and many other organisms and they applied to all of them as well
    • Genes and the Environment
      • Genes provide the plan for development
      • How the plan unfolds depends on the environment
      • Example:
        • Sunflower has genes for height and color of flowers
        • But these traits are also influenced by climate, soil conditions and water availability