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Mendelian Genetics. Mendel studied 7 traits He studied one trait at a time He began his work by breeding together two True Breeding plants. A True Breeding plant self-pollinates and always has offspring that share its traits.

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mendelian genetics
Mendelian Genetics
  • Mendel studied 7 traits
  • He studied one trait at a time
  • He began his work by breeding together two True Breeding plants.
  • A True Breeding plant self-pollinates and always has offspring that share its traits.
  • Example: Tall plants always produce tall plants. Short plants always produce short plants.
mendel s experiments
Mendel’s Experiments
  • Mendel asked, “What happens if I cross a true breeding tall plant with a true breeding short plant?”
  • _____________________________________

According to the theory of blending, what will be the results of this cross?

Medium tall plants

mendel s results
Mendel’s Results
  • What were the ACTUAL results of a cross between a true breeding tall and a true breeding short plant?
  • All of the offspring were TALL.
  • True breeding plants are the
    • Parents or P generation
  • The offspring of the P generation are the
    • First Filial (filial = son in Latin) or F1 generation
how did mendel conduct his experiment
How did Mendel conduct his Experiment?
  • Flower Worksheet

♂= male

♀=female

mendel s experiment
Mendel’s Experiment
  • Mendel removed the stamen (♂) from the flower of a TALL plant. The stamen is made of the anther (covered in pollen) and the filament.
  • He then removed pollen from the anther and brushed it on the stigma (♀) of the flower of a SHORT plant.
mendel s results1
Mendel’s Results
  • The plants produced seeds.
  • The seeds were planted
  • Every seed produced a TALL plant
  • Mendel’s First Conclusion: biological inheritance is determined by factors that are passed from one generation to the next.
  • Today we know these factors as genes.

F1 generation

P generation

mendel s second experiment
Mendel’s Second Experiment
  • Mendel crossed plants from the F1 generation together.
  • He created thousands of crosses this way.
  • Each flower produced seeds.
  • Thousands of these seeds were planted and grew into the F2 generation.
mendel s results of the f 1 cross
Mendel’s Results of the F1 Cross
  • Mendel observed the thousands of plants he grew from seeds.
  • He found the missing trait had reappeared!!
  • Among the new F2 generation there was a

3:1 ratio of Tall to Short Plants

P

generation

F1

generation

F2

Generation

mendel s second conclusion
Mendel’s Second Conclusion
  • Second Conclusion: Principle of dominance – Some alleles are dominant and some are recessive. An organism with one or two dominant alleles for a particular form of a trait will have that form (tall plant).
  • An organism with two recessive forms of a trait will have that form (short plant).

**********************

  • An organism inherits TWO alleles for every trait. One from its mother and one from its father.
rules for genetic problems
Rules for Genetic Problems
  • Two alleles for a gene are represented with the same letter.
  • Dominant alleles are represented with an uppercase letter, and recessive alleles are represented with a lower case letter.
  • Example: Tall allele = T; Short allele = t
  • Example: Round seeds = R; Wrinkled seeds =r
  • The letter representing the gene is usually the first letter of the dominant trait.
rules for genetic problems1
Rules for Genetic Problems
  • Try this:
    • A pea plant has two alleles for seed color.
    • Yellow is the dominant seed color
    • Green is the recessive seed color.
    • What is the symbol for yellow seed color?_____________
    • What is the symbol for green seed color? _____________

Y

y

rules for genetic problems2
Rules for Genetic Problems
  • Since a plant inherits two alleles for seed color it may inherit any of the following genetic combinations
    • YY = yellow seeded plant
    • Yy = yellow seeded plant
    • yy = green seeded plant. 
  • Remember: A recessive trait appears only when an organism inherits two recessive alleles!
more vocabulary
More Vocabulary
  • Homozygous genes = same alleles for the trait (YY, yy) = pure
  • Heterozygous genes = different alleles for the trait (Yy) = hybrid
  • Genotype = genetic make-up of an organism.
  • Phenotype = physical characteristic of an organism.
punnett squares
Punnett Squares
  • Named after R.C. Punnett, British geneticist, 1875-1967
  • Used to understand the probability of the outcome of a genetic cross.
practice
Practice
  • Cross 1 - Make a Punnett Square of a cross between the P generation of a yellow seeded plant (YY) and the F1 generation (Yy)
  • Cross 2 - Make a Punnett Square of a cross between the P generation of a green seeded plant (yy) and the F1 generation (Yy)
  • What is the phenotype and genotype for the offspring in cross 1? Cross 2?
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