Mendel and his Peas

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Mendel and his Peas

• Chapter 5 Lesson 1

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Chapter 5 Genetics
How are traits passed from parents to offspring?
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Mendel and his Peas

• Why did Mendel perform cross-pollination
  experiments?
• What did Mendel conclude about inherited traits?
• How do dominant and recessive factors interact?

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Gregor Mendel

• the father of genetics

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Genetics

• the study of how traits are passed from parents
  to offspring
• (the study of inheritance)

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Heredity

• the passing of traits from parents to offspring

Trait a genetically determined characteristic or
condition
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Gregor Mendel

• Mendel's work was done about 140 yrs. ago, but
  even now much of what we know about genetics is
  based on Mendel's work and illustrated by it.

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Gregor Mendel

• was born in 1822 on a farm in Heinzendorf,
  Austria
• At age 21 entered the Augustinian order of the
  Roman Catholic Church
• As a monk he - studied science at the University
  of Vienna and became an excellent mathematician

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Gregor Mendel

• As a school teacher - he engaged in many
  scientific activities
• At a monastery - he began a program of selective
  breeding of peas. After 8 yrs. of raising 30,000
  pea plants and recording and classifying many
  pages of notes, he wrote a paper with his
  conclusions called Mendelian Genetics (1865).

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Mendels Experimental Methods

• Mendel studied genetics by doing controlled
  breeding experiments with pea plants.
• There are two types of pollination
• self-pollination
• cross-pollination

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Self-Pollenation
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Mendels Experimental Methods

• When a true-breeding (purebred) plant
  self-pollinates, it always produces offspring
  with traits that match the parent.
• Mendel cross-
• pollinated pea
• plants himself
• and recorded
• the traits that
• appeared.

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Cross-Pollenation
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Mendels Experimental Methods
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Mendels Results

• Once Mendel had enough true-breeding plants for a
  trait he wanted to test, he cross-pollinated
  selected plants.
• Plants are called hybrids if they come from
  true-breeding parent plants with different forms
  of the same trait.

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First-Generation Crosses
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Mendels Results
hybrid Science Use the offspring of two animals
or plants with different forms of the same
trait Common Use having two types of components
that perform the same function, such as a vehicle
powered by both a gas engine and an electric motor
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Mendels Results

• Mendel also cross-pollinated hybrid plants.
• He observed that offspring of hybrid crosses
  always showed traits in a 31 ratio.

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Second-Generation (hybrid) Crosses
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Mendels Results
Mendel recorded traits of offspring from many
hybrid crosses.
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Mendelian Genetics

• His paper was the first recorded study of how
  traits pass from one generation to the next.
• Mendel also was the first to use the mathematics
  of probability to explain heredity.

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Mendelian Genetics

• When Mendel's paper was published, in 1865, it
  received little attention, and was rarely cited
  by botanists or biologists during the next 34
  years.
• In 1900, Mendel's work was cited by three
  botanists, writing in different parts of Europe
  Hugo de Vries, in Amsterdam Carl Correns, in
  Tübingen and Eric Von Tcshermak, in Esslingen,
  Austria.

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Mendel's Theories

• the concept of unit characteristics
• the concept of dominant and recessive
• the concept of segregation

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the concept of unit characteristics
Mendel concluded that two factors, one from the
sperm and one from the ovum, control each
inherited trait.
if factors were the same - purebred TT (tall)
tt (short) if factors were not the same - hybrid
Tt (tall)
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The Concept of Dominant and Recessive
Dominant trait - a genetic factor that blocks
another genetic factor. Recessive trait - a
genetic factor that is blocked by the presence of
a dominant factor. The dominant allele (factor)
completely masks the presence of the recessive
allele (factor).
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the concept of segregation
Mendel reasoned that when a cell forms gametes,
the genes separate (segregate) so that there is
only 1 gene for each characteristic in each
gamete.
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Principles of Heredity

1. Traits are controlled by alleles on chromosomes.
2. An alleles effect is dominant or recessive.
3. When a pair of chromosomes separates during
   meiosis the different alleles for a trait move
   into separate sex cells.