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2. 11-1 The Work of Gregor Mendel
photo credit: W. Perry Conway/CORBIS
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3. Remember? Genes are sets of instructions found on chromosomes (DNA) which are passed from parents to offspring. Therefore the fertilized egg would have two genes for every characteristic (one from each parent). The two genes that govern the same characteristic are known as alleles.

4. Gregor Mendel

5. 1. Gregor Mendel, "The Father of Genetics”
Born in Austria (1822)
Discovered basic principles of heredity.
c) Used pea plants – two forms (or traits) for each of the characteristics studied.
d) His observations justify Darwin’s theory of evolution by natural selection.

6. a) Ask a question: How are traits inherited
a) Ask a question: How are traits inherited? B) Form a hypothesis: Inheritance has a pattern. C) Test the Hypothesis: Cross true- breeding plants with offspring. D) Analyze the results: Identify patterns in inherited traits. E) Draw conclusions: Traits are inherited in predictable patterns.
2. Scientific Method

7. What are the two forms (or traits) for, say, the characteristic of flower color in peas?
Purple and White

8. 3.

9. Other Characteristics Mendel Studied

10. 4.

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Genes and Dominance 5.
a) Each original pair of plants is the P (parental) generation.
b) The offspring are called the F1, or “first filial,” generation.
c) The offspring of crosses between parents with different traits are called hybrids.
d) The F1 hybrid plants all had the character of only one of the parents.
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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
6. The principle of dominance states: Some alleles are dominant and others are recessive.
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Genes and Dominance 7.
a) An organism with a dominant allele for a trait will always exhibit that form of the trait.
b) 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
8. Segregation
a) Mendel crossed the F1 generation with itself to produce the F2 generation.
b) Traits controlled by recessive alleles reappeared in ¼ of the F2 plants.
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17. 9. Mendel’s Second Experiment
First-generation plants self-pollinated: Result was one purple-flowered (PP) purebred; two purple-flowered (Pp) hybrids; and one white (pp) purebred.
Pp X Pp = 1 PP, 2 Pp and 1 pp
Mendel concluded that purple flower color in pea plants was dominant, and became the expressed trait, (uppercase P). The white flowers in the pea plant was recessive, becoming the hidden trait (lower case p) if paired with a dominant allele.

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Segregation
10. 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. Not everyone is a tongue-roller!

23. Punnett Square

25. Probability

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Segregation
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.
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27. Not all inherited traits follow those examples by having only two forms for each characteristic.
Examples of Codominance (both alleles are equally dominant): Roan Fur in Cattle: Cattle can be red, white or roan (mixed) Human Blood Type AB Snapdragon Flower Colors

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11-1
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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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34. END OF SECTION