Understanding Inheritance

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Understanding Inheritance
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Traits
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Detached Earlobes
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Tongue rolling
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Dimples
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Cleft Chin
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Cross Left thumb over right
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See Colours Red and Green
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Straight Hair Line vs Widows Peak
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Key Terms

• Selective breeding
• Artificial breeding
• Pure Bred
• Gregor Mendell
• Traits
• Self-fertilization vs. Cross Fertilization
• Monohybrid cross
• Dihybrid cross
• P generation
• F1 and F2 generation
• Dominant vs. recessive traits
• Genotype vs. Phenotype
• Heterozygous and Homozygous alleles

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Early Genetics

• Selective breeding was the earliest form of
  understanding about genetics
• Selective breeding (a form of artificial
  breeding) is when people breed certain animals or
  plants in order to produce a desired offspring
• For example Horses that developed strong muscles
  were bred with other horses that had strong
  muscles in order to make race horses.

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Early Genetics

• Pure bred horses are used by horse breeders to
  produce offspring that are quicker, stronger, and
  more durable for races.

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Early Genetics

• Prior to the 1850s and 1860s people did not
  understand how genetics worked.
• In the 1600s, live sperm was discovered using a
  microscope. It was believed that a tiny person
  was inside the sperm and that this person would
  develop inside the mother
• In the 1800s, scientists realized that people
  inherit their characteristics from both parents.
• However, they believed in blended inheritance
  (i.e. if mother has blond hair and father has
  black, the child will have brown hair.

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Gregor Mendel The Pioneer of Genetics
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Gregor Mendel The Pioneer of Genetics

• Gregor Mendel was the first to conduct a
  scientific experiment on inheritance
• Mendel discovered inheritance by studying garden
  peas

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Gregor Mendels Observations

• Gregor Mendel noticed that some garden pea plants
  were tall while others are short, some pea plants
  had different flower position

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Gregor Mendels Observations

• some pea plants were round while others were
  wrinkled, and some pea pods were full while
  others flat
• Mendel referred to these characteristics as
  traits.

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Gregor Mendels Observations

• Mendel also noticed that pea plants could
  self-fertilize and cross-fertilize.
• Self-fertilization means that a plant is able to
  reproduce with itself and produce offspring.
• Cross-fertilization means that a plant reproduces
  with another plant to produce an offspring
  (sexual reproduction).

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Cross-Fertilization Vs. Self-Fertilization
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Mendels Experiment

• Mendel used pea plants that self-fertilize for
  his experiment.
• This meant that the offspring made by that plant
  will be the same as the parent
• This is referred to as true breeding or pure
  breeding.
• Mendel then selectively fertilized a pure bred
  green pea plant with a pure breed yellow pea
  plant.
• In Genetics this is called a cross. (a.k.a cross
  fertilization)

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Mendels Experiment

• Cross Fertilization

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• Before we look at the results let us clarify some
  key terms

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Key Terms

• Since Mendel was only examining the colour of the
  pea pod, it is called a monohybrid cross.
• If for instance Mendel was examining both the
  colour and the size of the pea plant, then it
  would be called a dihybrid cross.

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Key Terms

• In a test cross (cross pollination) the parent
  generation is called P generation
• The first offspring is called F1 generation
• The children of the F1 generation is the F2
  generation.
• And so forth

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• Back to the results of Mendels Experiment

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Mendels Results

• When Mendel cross fertilized pure bred green pea
  plants with pure bred yellow pea plants
• The offspring were all green pea plants.

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Mendels Experiment

• Through this experiment Mendel realized that some
  traits (i.e green coloured pea plants) are
  dominant to other traits (i.e. yellow coloured
  pea plants).
• The green coloured allele for pea plants is
  therefore dominant to the yellow coloured allele.
• The yellow coloured allele is therefore
  recessive.

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Mendels Experiment (Part 2)

• Mendel then crossed two of the F1 generation pea
  plants from the original experiment and
• The result was that ¾ of the offspring were green
  and ¼ were yellow

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Genotype vs. Phenotype

• Alleles are often represented using upper-case
  letters and lower-case letters.
• Recall Mendels experiment
• Which colour allele is dominant?

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Genotype

• Since the green allele is dominant, we can
  represent it using the letter G.
• On the other hand, the yellow allele is recessive
  and we can represent it using the letter g.
• Remember each trait has 2 alleles
• This makes it possible to have 3 different
  combinations
• 1. GG 2.Gg 3. gg

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• Let us look at a different example

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Genotype vs. Phenotype
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Genotype vs. Phenotype

• Genotype refers to the combination of alleles and
  the phenotype refers to the physical
  characteristics (e.g. observable traits) produced
  by the alleles.

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Genotype

• If the gene contains two dominant alleles (e.g.
  GG) we call this genotype homozygous dominant.
• If the gene contains two recessive alleles (e.g.
  gg) we call this genotype homozygous recessive.
• If the gene contains one dominant and one
  recessive allele (e.g. Gg) we call this genotype
  heterozygous.

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Genotype vs. Phenotype
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homework

• Pg.207 4, 6, 9, 11