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Mendel

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Title: Mendel


1
Mendels Principles
2
Who was Gregor Mendel?
  • He was an Austrian monk born in 1822.
  • He is known as the Father of Genetics for his
    experiments and observations of the inherited
    traits of pea plants.
  • He cross-pollinated pea plants which were
    true-breeding (producing offspring identical to
    the parents) for several traits.

3
What are Traits?
  • A trait is a specific characteristic that varies
    from one individual to the next.
  • Mendel chose 7 pea plant traits to study
  • seed shape, seed color, flower color, pod shape,
    pod color, flower position, and plant height.
  • HOWEVER, he studied only ONE TRAIT at a time!
    This is what helped make his results so
    conclusive!

4
Mendels Experiment!
  • He wanted to fertilize seeds by joining male
    female gametes from 2 different plants with
    different traits (ex Tall short plants).
  • To prevent self-pollination, he cut away the
    pollen-bearing male parts from one plant.
  • Then, dusted pollen from another plant onto the
    egg-bearing female part of the first plant.
  • This process is referred to as cross-pollination.

5
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6
  • Mendel cross-pollinated true-breeding tall plants
    with true-breeding short plants.
  • He called these original pair the parent
    plants or
  • P generation.

7
  • Their offspring, or the F1 generation were all
    tall.
  • The offspring of crosses between parents with
    different traits are called hybrids.

8
  • Mendel then let the F1 generation self-pollinate
    to create the second generation (F2 generation).

9
  • Some of the F2 offspring were tall and some were
    short.
  • The ratio consistently added up to 3 tall 1
    short.

10
Mendels Results
  • Based on Mendels work, we now know that
  • A gene is a segment of DNA that determines a
    trait.
  • Ex eye color
  • Alleles are different forms of a gene.
  • Ex brown, blue, green, or hazel eyes

Mendels results led him to three basic
principles
Mendels Discoveries Results
11
The Principle of Dominance
  • In general, one allele is dominant to another.
  • The recessive allele will be expressed only if
    the dominant allele is not present.
  • Expressed as the lower case letter of the
    dominant trait.
  • Ex Short is a recessive trait tt
  • The dominant allele is always expressed even if
    combined with the recessive allele. It masks the
    recessive one.
  • Expressed with a CAPITAL letter.
  • Ex Tall is a dominant trait TT or Tt

12
The Principle of Dominance continued
  • The combination of alleles is called the
    genotype.
  • If both alleles are the same, the individual is
    homozygous.
  • If the alleles are different, the individual is
    heterozygous.
  • The physical appearance, or observable trait is
    the phenotype.

13
The Principle of Segregation
  • When gametes form, the alleles MUST separate from
    each other.
  • Each gamete carries only a single allele for each
    gene.

14
Parents (P)
gametes
F1
gametes
F2
Circle Genotype Hetero/Homo-zygous Phenotype Generation Gamete? (y / n)
1
3
7
14
TT
homozygous
tall
no
P
n/a
T
n/a
yes
n/a
Tt
no
tall
F1
heterozygous
tt
short
F2
no
homozygous
15
Principle of Independent Assortment
  • When examining 2 different traits at the same
    time (height seed color), Mendel noticed that
    all possible combinations were expressed in the
    F2 generation.
  • Ex tall green, tall yellow, short green,
    short yellow
  • Different traits are inherited independently of
    each other, so that there is no relation, for
    example, between a plants height and its seed
    color.

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