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Mendel 2


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  • 1. More of Mendel pp. 270 - 274
  • 2. 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
  • 3. Does the segregation of 1 pair of alleles affect the segregation of another pair of alleles?
  • 4.
    • 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
  • 5.
    • What is the phenotype of the F1 offspring?
    • What is the genotype of the F1 offspring?
  • 6. 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?
  • 7. Now cross these hybrid (RrYy) plants on a new 4X4 Punnett Square
  • 8.  
  • 9. 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
  • 10. 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.
  • 11. Mendel’s 4 Principle’s
    • Inheritance of biological characteristics is determined by genes
    • Principle of Dominance
    • Law of Segregation
    • Principle of Independent Assortment
  • 12. Exceptions to Mendel
    • Genetics more complicated
    • Some alleles are neither dominant nor recessive
    • Many traits are controlled by multiple alleles or multiple genes
  • 13. 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
  • 14.  
  • 15. 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
  • 16.  
  • 17. 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
  • 18.  
  • 19. 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
  • 20. 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
  • 21. 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
  • 22.