Exploring Mendelian Genetics

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Exploring Mendelian Genetics

• Two trait Crosses
• 11.3

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Dihybrid crosses

• All of the crosses discussed so far have involved
  only a single trait.
• Ex. Tt
• However, Mendel also conducted crosses that
  examine the inheritance of two different traits.
• He wondered if both traits would always appear
  together or if they would be expresses
  independently of each other.

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Two-Factor Cross

• Mendel crossed pure-breeding plants for two
  traits
• Round, Yellow x wrinkled, green
• RRYY x rryy
• All F1 offspring produced were Round, Yellow
• Yellow is dominant to Green
• Round is dominant to wrinkled
• Genotype of F1 offspring is RrYy

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A dihybrid cross involves two traits.

• Mendels dihybrid crosses with heterozygous
  plants ( F1 generation) yielded a 9331
  phenotypic ratio for the F2 generation.

• Mendels dihybrid crosses led to his second
  law,the law of independent assortment.
• The law of independent assortment states that
  allele pairs separate independently of each other
  during meiosis.
• Independent assortment helps account for the many
  genetic variations observed in plants, animals,
  and other organisms.

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Dihybrid Cross
RrYy x RrYy
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Dihybrid Cross
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Dihybrid Cross
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Summary of Mendels Principles

• Principle of Heredity
• Inheritance of biological characteristics is
  determined by individual units known as genes.
  Genes are passed from parents to offspring.
• Principle of Dominance
• In cases in which two or more alleles of the gene
  for a single trait exist, some gene forms may be
  dominant and others recessive.

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Summary of Mendels Principles

• Principle of Segregation
• In most sexually reproducing organisms, each
  adult has two copies of each gene- one from each
  parent. These genes are segregated from each
  other when gametes are formed.
• Principle of Independent Assortment
• The alleles for different genes usually segregate
  independently from one another.