MENDEL’S WORK
Key Concepts
What were the results of Mendel’s experiments or crosses?
What controls the inheritance of traits in organisms?
Key Terms
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Heredity
Trait
Genetics
Fertilization
Purebred
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Gene
Alleles
Dominant allele
Recessive allele
hybrid
Mendel’s Work
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Mendel experimented with thousands of
Pea plants looking at their different traits
to understand the process of heredity. His
discoveries form the foundation of genetics.
Heredity –the passing of physical
characteristics from parents to
offspring
Trait- each different form of a
characteristic
Genetics – the study of heredity
Mendel’s Experiments
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Flowering Plant anatomy
Pistil – produces the female sex
cells or eggs
Stamens – produce pollen which contains the male
sec cells or sperm
Fertilization is when the egg and sperm join forming
a new organism
In plants the pollen must reach the pistil for
fertilization to occur. This is called pollination
Pollination
Pea plants usually selfpollinate. The pollen from their
stamens lands of the same
plants pistils.
 Mendel developed a method
to cross-pollinate pea plants.
He took pollen from one pea
plant and brushed it onto the
pistil of another.
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Crossing Pea Plants
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Mendel crossed plants with
contrasting traits
Ex. Tall plants with short plants
Started with purebred plants – a
purebred organism is one who is
the offspring of many
generations of that have the
same trait
The F1 Offspring
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Mendel crossed purebred tall with purebred short
Parental (P) generation
Tall x short
Offspring from the cross are called F1 (filial)
All F1 offspring were tall
F2 offspring
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When F1 were full grown,
Mendel allowed them to
self-pollinate
F2 were a mix of tall and
short
¾ were tall and ¼ were
short
Experiments with OtherTraits
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Mendel crossed pea plants with other contrasting traits
such as seed shape, seed color, seed coat color, etc.
In all crosses the F1 generation had only 1 form of the trait
In the F2 generation the “lost” form reappeared in ¼ of
the plants.
Dominant and Recessive Alleles
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Mendel’s Conclusion
factors control the inheritance
of traits in peas.
They exist in pairs
The female parent contributes
one factor and the male parent
contributes the other factor
One factor in a pair can mask
or hide the other factor
Genes and Alleles
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Genes – factors that
control a trait
Alleles – different forms of
a gene
An organisms traits are controlled by the alleles it
inherits from its parents.
Some alleles are dominant, while others are
recessive
Dominant allele – trait always shows
Recessive allele –trait is hidden whenever dominant
allele is present
Alleles in Mendel’s Crosses
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Stem Height Cross
P generation tall tall x short short
F1 generation all were tall short- Look tall
F2 generation ¼ tall tall - look tall
¼ tall short + ¼ short tall – look tall
¼ short short – look short
Symbols for alleles
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Letters are used to represent
alleles
Capital letters are used for
dominant alleles
Lowercase letters are used for
recessive alleles
Purebred tall = TT
Purebred short = tt
Hybrid (one of each) =Tt
Significance of Mendel’s Contribution
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Before Mendel most people thought that the traits of an
individual were a blend of their 2 parents.
If they blended the Tt plants should be medium height
Mendel found out that traits are determined by
individual alleles some of which are dominant and some
recessive.
Recessive traits may seem to disappear in the offspring
only to reappear in the next generation
Mendel’s work was not recognized during his lifetime, but
was rediscovered in 1900. He is now
considered the Father of Genetics.
Sources
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http://kentsimmons.uwinnipeg.ca/cm1504/mendel.htm
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http://www.exploringnature.org/db/detail.php?dbID=45&detID=2290
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http://ncse.com/files/images/pea_plant.preview.jpg
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http://library.thinkquest.org/28751/review/plants/6.html
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http://www.cactus-art.biz/notebook/Dictionary/Dictionary_C/dictionary_cross_pollination.htm
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http://academic.kellogg.edu/herbrandsonc/bio111/genetics.htm
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http://www.bioinformatics.nl/webportal/background/mendelinfo.html
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http://www.absoluteastronomy.com/topics/Experiments_on_Plant_Hybridization
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http://www.csulb.edu/~kmacd/361-6-Ch2.htm
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http://library.thinkquest.org/17109/tutorial.htm

http://www.learner.org/interactives/dna/genetics3.html
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http://cynthialeitichsmith.blogspot.com/2010/06/guest-post-sharron-l-mcelmeelon.html