Principles of Genetics and Punnett Squares

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Principles of GeneticsandPunnett Squares
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Principles of Genetics

• Traits / characteristics are passed on from one
  generation of organisms to the next generation.
• The traits of an organism are controlled by
  genes.
• Organisms inherit genes in pairs, one gene from
  each parent.

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• Some genes are dominant, whereas other genes are
  recessive.
• Dominant genes hide recessive genes when both are
  inherited by an organism.
• Some genes are neither dominant nor recessive.
  These genes show incomplete dominance.

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Punnett Squares

• Used to show possible ways that genes can combine
  at fertilization
• Predict what traits offspring might get
• For example
• Tt x Tt
• To predict the offspring we can use a special
  chart called a Punnett Square
• This chart will show the possible gene
  combination in a cross between 2 organisms

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Example

• Tt x Tt
• 
  T t
  
• T
• t

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Tt x Tt

• Results
• TT 25 Purebred Tall
• Tt 50 Hybrid Tall
• tt 25 Purebred Short

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Vocabulary (Refer to Punnett Square sheet for
examples)

• Genotype actual gene makeup of an organism
• (BB)
• Phenotype physical appearance visible
  characteristics (Brown eyes)
• Homozygous BB or bb (same)
• Heterozygous - Bb (different)
• Hybrid an organism with two different genes for
  a particular trait (heterozygous)
• Purebred an organism with two of the same genes
  for a particular trait (homozygous)

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• LET US PRACTICE
• YOU CAN DO IT!!!!!!