Probability and Ratios

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Probability and Ratios
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Probability

• The likelihood that a particular event will occur.

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Probability

• Can determine probability from completed Punnet
  Squares
• Example

Probability of first offspring being a male
Probability of second offspring being a male
Probability of third offspring being a male
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Probability

• Probability does not change after traits show up
  in an offspring. Same chance still exists for
  every possibility of being expressed.

Probability of first offspring being a male 1/2
Probability of second offspring being a male 1/2
Probability of third offspring being a male 1/2
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Ratios

• Comparing the number of phenotypes or genotypes
  of the possible offspring
• Phenotypic Ratio
• Comparing the amount of offspring that express
  each physical trait in a given cross
• Genotypic Ratio
• Comparing the amount of offspring that express
  each allele combination in a given cross

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Example
b
B

• Phenotypic Ratio
• There are three browns and one green.
• The ratio is 31
• Genotypic Ratio
• There is one homozygous dominant, two
  heterozygous, and one homozygous recessive.
• The ratio is 121

BB
Bb
B
b
bb
Bb