Download 12.2 * What is Heredity?

12.2 – What is Heredity?
Essential Questions:
1.
What did Mendel observe?
2.
How do alleles affect inheritance?
Gregor Mendel
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Gregor Mendel
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1822-1884
Austrian Monk
“Father of Genetics”
What did Mendel observe?

Heredity is the passing of physical characteristics, or
traits, from parents to offspring.
Mendel’s Experiments
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Mendel used pea plants
for his experiments.
Pea plants are usually selfpollinating.
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They pollinate themselves.
Egg cells and sperm cells
from the same plant join –
Fertilization
Mendel’s Experiments
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Mendel cross-fertilized the plants himself to see what the
offspring of two different pea plants would look like.
Mendel’s Experiments
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Mendel started with a purebred, an organism that is the
offspring of many generations of organisms that show the
same traits.
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Two purebred tall pea plants will always produce a tall offspring.
The F1 and F2 Generation
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Mendel crossed purebred tall plants with purebred short
plants. These are the parent plants (P).
The first generation of offspring (F1) were all tall.
These were allowed to self-pollinate.
The second generation (F2) were mixed.
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3 tall for every 1 short.
What did Mendel observe?
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In all of Mendel’s crosses, he found that only one form of
the trait appeared in the F1 generation.
However, in the F2 generation, the “lost” form of the trait
always reappeared in about 1/4th of the plants.
How do alleles affect inheritance?
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Mendel’s Conclusions:
1.
2.
3.
Genetic information controls the
inheritance of traits.
The factors that control each trait
exist in pairs.
One factor can hide or mask the
other.
How do alleles affect inheritance?
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Genes control the inheritance of traits.
Alleles are the different forms of a gene.
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One from the male and one from the female.
Dominant alleles make a trait show in an organism.
Recessive alleles are masked when a dominant allele is
present.
How do alleles affect inheritance?
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If an organism has one dominant allele and one recessive
allele for the same trait, it is called a hybrid.
How do alleles affect inheritance?
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The symbol for a dominant allele is an uppercase letter.
The symbol for a recessive allele is a lowercase letter.
The Importance of Mendel’s Work.
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Mendel showed that traits are determined by genes
passed from parent to offspring by way of alleles.
Before Mendel, people thought that the traits of an
individual organism were simply a blend of the parents’.
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Lamarckism – If a man with one arm (which he lost in an
industrial accident at age 27 BTW) had a child, there is a
chance that the child would be born with one arm.