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11.1 THE WORK OF GREGOR MENDEL

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THE WORK OF GREGOR MENDEL (THE PEA MONK) 1. Every living thing- plant or animal, microbe, or human being has a set of characteristics inherited from its parents ... – PowerPoint PPT presentation

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Title: 11.1 THE WORK OF GREGOR MENDEL


1
11.1 THE WORK OF GREGOR MENDEL
  • (THE PEA MONK)

2
  • 1. Every living thing- plant or animal, microbe,
    or human being has a set of characteristics
    inherited from its parents or parent.

3
  • Heredity holds the key to what makes each species
    unique.
  • The scientific study of heredity is genetics.

4
  • 2. Gregor Mendel, an Austrian monk, had a very
    great life studying math and science, teaching
    high school, and piddling in the monastery
    gardens.

5
  • This man was fascinated with
  • ordinary garden peas. He
  • could never ever be bored
  • because these things are the
  • source of a great deal of knowledge ?

6
  • 3. Pea flowers
  • produce pollen,
  • which contains the
  • male plants
  • reproductive cells
  • or sperm (stamen).
  • The flowers also
  • have female parts,
  • which produce egg
  • Cells (carpel).

4 5 make up the male parts pollen 2 3
make up the female part.
7
  • 4. During sexual reproduction, the male and
    female cells join, a process called
    fertilization.
  • Fertilization produces a new cell,
  • which develops into a tiny
  • embryo encased within a seed.

8
  • 5. Pea flowers are normally self-pollinating,
    which means that sperm cells in pollen fertilize
    the egg cells in the same flower.
  • The seeds that are produced inherit
  • all of their characteristics from the
  • single plant that bore them. They
  • have a single parent!

9
  • 6. Mendel discovered that his pea plants were
    true-breeding, meaning that if they were allowed
    to self-pollinate, they would produce offspring
    identical to themselves!!
  • One stock of seeds would produce only tall
    plants, another short ones. One line produced
    green seeds, another yellow ones.

10
  • 7. Mendel wanted to produce seeds by joining
    sperm and eggs from two different plants. To do
    this he had to prevent self-pollination!!!
  • This is what he did! He cut away the
    pollen-bearing male parts then dusted pollen from
    another plant onto the flower.

11
  • 7. This process is called cross-pollination.
  • It produced seeds that had two different plants
    as parents!
  • This made it possible for Mendel to cross-breed
    plants with different characteristics, and then
    study the fascinating results!!

12
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13
  • 8. Mendel studied seven different pea plant
    traits.
  • A trait is a specific characteristic that varies
    from one individual to another.
  • Each of the 7 traits Mendel studied had two
    contrasting characters, such as green/yellow
    seeds color, tall/short plants, etc.

14
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15
  • 9. Mendel crossed plants with contrasting
    characters and studied their offspring.
  • He called the original set of parents the P
    (parental) generation. He called the offspring
    the F1 first filial generation.
  • The offspring of crosses between parents of diff
    traits are called hybrids.

16
Hybrids from a cross between a tall plant and a
short plant
17
  • 10. Mendel was a busy man! He was also surprised!
    All of the offspring in the F1 generation had the
    character of ONLY one of the parents!
  • The character of the other parent seemed to have
    disappeared!!...Was this magic? Or was there
    another explanation?

18
Hybrids from a cross between a tall plant and a
short plant
19
  • 11. Mendel drew two conclusions
  • 1. Biological inheritance is determined by
    factors that are passed from one generation to
    the next.
  • (Today, we call the chemical factors that
    determine traits genes. Each of the traits Mendel
    studied was controlled by one gene that occurred
    in two contrasting forms.)

20
  • 11. (These contrasting forms produced the
    different characters of each trait. The diff
    forms of a gene are called alleles).

21
Purple
X
Axial
X
Yellow
X
X
X
X
X
22
  • 2. The Principle of dominance states that some
    alleles are dominant others are recessive.
  • An organism with the dominant form of an allele
    will always exhibit that form of the trait.

23
  • 2. An organism with the recessive allele for a
    particular form of a trait will exhibit that form
    ONLY when the dominant allele for that trait is
    NOT present!!

24
  • 12. Mendel wanted to know if the recessive
    alleles had disappeared, or were they still
    present in the F1 plants??
  • He allowed all seven kinds of F1 hybrid plants
    to produce an F2 (2nd filial) generation by
    self-pollination.

25
  • 13. The results of the F1 cross were REMARKABLE!!
  • When Mendel compared the F2 plants, he
    discovered that the traits controlled by the
    recessive alleles had reappeared!!
  • Roughly ¼ of the F2 plants showed the trait
    controlled by the recessive allele!!!

26
P Generation
F1 Generation
F2 Generation
Recessive allele traits reappeared in about ¼ of
the F2 plants
27
  • 14. WHY did the recessive alleles seem to
    disappear in one generation and reappear in the
    next???
  • The answer is segregation!!!
  • The reappearance of the recessive trait (short
    plant in this case) indicated that it had somehow
    become separated from the allele for tallness.

28
  • So how did this separation or segregation occur?
    Mendel suggested that the alleles for tallness
    and shortness in the F1 plants segregated from
    each other during the formation of the sex cells,
    or gametes.

29
  • 15. If F1 plants inherit an allele for tallness
    from one parent and an allele for shortness from
    another parent, all the F1 plants are tall
    because the allele for tallness is dominant.

30
  • When each F1 plant flowers and produces gametes,
    the two alleles segregate from each other so that
    each gamete carries only a single copy of each
    gene.
  • Therefore, each F1 plant produces two types of
    gametes ---those with the allele for tallness and
    those with the allele for shortness.

31
Figure 11-5 from pg. 266Draw and LabelGamete
formation
alleles
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