1. 11-1 The Work of Gregor Mendel
photo credit: W. Perry Conway/CORBIS
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Gregor Mendel’s Peas
Gregor Mendel’s Peas
Genetics is the scientific study of heredity.
Mendel carried out his work with ordinary garden peas.
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Gregor Mendel’s Peas
Mendel knew that
the male part of each flower produces pollen
the female part of the flower produces egg cells.
To cross-pollinate pea plants, Mendel cut off the male parts of one flower and then dusted it with pollen from another flower.
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Gregor Mendel’s Peas
During pollination, pollen and egg cells join in a process called Fertilization.
Self-pollinating flowers had true-breeding pea plants that would produce offspring identical to themselves.
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Gregor Mendel’s Peas
Cross-pollination
Mendel was able to produce seeds that had two different parents.
To cross-pollinate pea plants, Mendel cut off the male parts of one flower and then dusted it with pollen from another flower.
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Genes and Dominance
Genes and Dominance
A trait is a specific characteristic that varies from one individual to another.
Plants with contrasting traits were crossed first.
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Genes and Dominance
P generation - parents
F1 generation – 1st offspring
Crosses between parents with different traits produce hybrids.
The F1 hybrids all showed to Dominant character.
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8. Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s F1 Crosses on Pea Plants
When Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.
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9. Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s Seven F1 Crosses on Pea Plants
Mendel’s F1 Crosses on Pea Plants
When Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.
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Genes and Dominance
Mendel stated that factors are passed from one generation to the next.
Today, we call the factors that determine traits genes.
Alleles – different variations of genes
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Genes and Dominance
The principle of dominance states that some alleles are dominant and others are recessive.
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Segregation
Segregation
Mendel crossed the F1 generation with itself to produce the F2 generation.
The traits controlled by recessive alleles reappeared in one fourth of the F2 plants.
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Segregation
Mendel's F2 Generation
F1 Generation
F2 Generation
P Generation
When Mendel allowed the F1 plants to reproduce by self-pollination, the traits controlled by recessive alleles reappeared in about one fourth of the F2 plants in each cross.
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
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14. Mendel’s 2nd Law of Segregation
Factors occur in pairs and separate during gamete formation only to recombine again during fertilization.
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Segregation
Alleles separate during gamete formation.
During gamete formation, alleles segregate from each other so that each gamete carries only a single copy of each gene. Each F1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness. The alleles are paired up again when gametes fuse during fertilization. The TT and Tt allele combinations produce tall pea plants; tt is the only allele combination that produces a short pea plant.
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11-1
Gametes are also known as
genes.
sex cells.
alleles.
hybrids.
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11-1
The offspring of crosses between parents with different traits are called
alleles.
hybrids.
gametes.
dominant.
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11-1
In Mendel’s pea experiments, the male gametes are the
eggs.
seeds.
pollen.
sperm.
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11-1
In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F1 generation consists of
all short plants.
all tall plants.
half tall plants and half short plants.
all plants of intermediate height.
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11-1
If a particular form of a trait is always present when the allele controlling it is present, then the allele must be
mixed.
recessive.
hybrid.
dominant.
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