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biology
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2. 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 (1) is the scientific study of heredity.
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Gregor Mendel’s Peas
Mendel knew that
the male part of each flower produces pollen, (containing sperm).
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 sexual reproduction, sperm and egg cells join in a process called fertilization.
Fertilization produces a new cell.
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Gregor Mendel’s Peas
Pea flowers are self-pollinating (2) – pollen fertilizes egg of the same plant
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Gregor Mendel’s Peas
Mendel had true-breeding (3) pea plants that, if allowed to self-pollinate, would produce offspring identical to themselves.
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Gregor Mendel’s Peas
Mendel used a process called cross-pollination (4) – sperm of one plant fertilizes egg of another plant
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 (5) is a specific characteristic that varies from one individual to another
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Genes and Dominance
Genes and Dominance
Mendel studied 7 pea plant traits, each with two contrasting characters.
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Genes and Dominance
Each original pair of plants is the P (parental) generation.
The offspring are called the F1, or “first filial,” generation.
The offspring of crosses between parents with different traits are called hybrids(6)
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12. 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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13. 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's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next.
Today, scientists call the factors that determine traits genes (7)
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Genes and Dominance
Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.
The different forms of a gene are called alleles (8)
Mendel’s second conclusion is called the principle of dominance.
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Genes and Dominance
The principle of dominance (9) states that some alleles are dominant and others are recessive.
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Genes and Dominance
An organism with a dominant allele for a trait will always exhibit that form of the trait.
An organism with the recessive allele for a trait will exhibit that form only when the dominant allele for that trait is not present.
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Segregation
The reappearance of the trait controlled by the recessive allele indicated that at some point the allele for shortness had been separated, or segregated (10) from the allele for tallness.
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Segregation
alleles for tallness and shortness in the F1 plants segregated from each other during the formation of the sex cells, or gametes (11)
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Protocols: Capital letter – dominant alleles Lower case letter – recessive alleles Capital before lower Two Capital letters – both alleles are dominant Two lower case letters – both alleles are recessive One capital and one lower case – one allele for dominance and one for recessive (hybrid)
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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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22. END OF SECTION