Mendels Pea Breeding Experiments

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• Mendels Pea Breeding Experiments

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Peas normally self pollinate. To prevent the
plants from pollinating themselves Mendel
emasculated the flowers and transferred pollen
manually.
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Mendel examined seven different characteristics
or traits. Each characteristic was present in
two forms or types. Flower colour could be purple
or white. Much of Mendels early work was to
ensure that each type bred true. Mendel had a
collection 14 true breeding types. True breeding
types are called purebreds.
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Mendel crosses two pure breeding plants. These
represent the parental (P) generation.
The seeds comprise the offspring or the first
filial generation (F1). The seeds are harvested
and planted the following spring. All offspring
are tall.
The F1 plants are allowed to self pollinate. The
seeds are harvested and sown the next year. Three
quarters of the plants (787 out of 1064) of the
second filial generation (F2) are tall while one
quarter (277) is short.
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Mendels First Experiment
Parental Generation (P) Purebred Tall Plants
Purebred Short Plants First
Filial Generation (F1) All Tall Plants Mendel
allowed the F1 to self-pollinate. F1
F1 Second Filial Generation (F2) 787 Tall
Plants 277 Short Plants 2.84
1.0 74 26 Mendel performed
this type of experiment for all seven
characteristics.
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Mendels Results
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Mendel Explains the Results Part I

• Contrasting characteristics or traits, such as
  tallness and shortness, are caused by internal
  factors that pass from parent to offspring by
  way of the gametes.
• Each individual, parent and offspring, possesses
  two factors for a trait. Offspring inherit 2
  factors for each trait, one from the male
  (pollen) and one from the female (ovule, i.e.
  egg). Thus these pairs factors must separate or
  segregate during formation of the gametes. (Law
  of Segregation)
• Purebred pea plants inherit 2 identical factors.
• Hybrid offspring inherit 2 contrasting factors, a
  different one from each parent.
• When both contrasting factors are present in an
  individual, one factor is suppressed. The
  suppressed factor is said to be recessive. The
  factor in evidence is said to be dominant.
  (Principle of Dominance)

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Mendel Explains the Results Part II
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Modern Terminology Associated with
Genetics Dominant trait Recessive
trait Homozygous (purebred) Heterozygous
(hybrid) Principle of Dominance Law of
Segregation Genes Alleles Genotype Phenotype Paren
tal Generation Filial Generation
View and read Mendels original paper at
http//www.mendelweb.org/home.html The hypertext
links provides both explanations and insight into
topics mentioned by Mendel.