KEY CONCEPT The inheritance of traits follows the rules of probability.

1
KEY CONCEPT The inheritance of traits follows
the rules of probability.
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Punnett squares illustrate genetic crosses.

• The Punnett square is a grid system for
  predicting all possible genotypes resulting from
  a cross.
• The axes representthe possible gametesof each
  parent.
• The grid boxes show
• the possible genotypesof the offspring.

• The Punnett square yields the ratio of possible
  genotypes and phenotypes.

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A monohybrid cross involves one trait.

• Monohybrid crosses examine the inheritance of
  only one specific trait.

-genotypic ratio is 4 Ff -Phenotypic ratio is 4
purple
4

• Ratios
• -Genotypic 121
• -Phenotypic 31

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• A testcross is a cross between an organism with
  an unknown genotype and an organism with the
  recessive phenotype.

Genotypic Ratio is 2Ff2ff 22
11 -Phenotypic Ratio is 2 purple2 white 22
11
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A dihybrid cross involves two traits.

• Ratio
• Mendels crossed heterozygous
• plants with 2 traits
• Always yielded a 9331
• phenotypic ratio.

• The law of independent assortment states that
  allele pairs separate independently of each other
  during meiosis.

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Heredity patterns can be calculated with
probability.

• Probability is the likelihood that something will
  happen.

• Probability applies to random events such as
  meiosis and fertilization.

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• 31 ratio if you look at one trait at a time (3
  are one type1 is another)
• 3 dominant1 recessive
• 3 tall plants1 short plant
• 9331 ratio if you look at two heterozygous
  plants at a time
• 9 both dominant 3 dominant, recessive 3
  recessive, dominant 1 both recessive