Dihybrid Cross Notes

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Dihybrid Cross Notes
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• 1. Determine dominant and recessive traits

• Carefully read the problem

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• 2. Assign letters for the trait

• B black
• b white
• H Hairy
• h no hair

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• 3. Determine genotype for parents

• Parents must have 4 alleles
• Heterozygous, black, hairless male Bbhh
• White heterozygous hairy female bbHh

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• 4. Draw the punnett square with 16 boxes

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• 5. Put parent gamete combinations on box

• Bbhh gametes
• Bh, Bh, bh, bh
• bbHh gametes
• bH, bh, bH, bh
• Bh Bh bh bh
• bH
• bh
• bH
• bh

BbHh BbHh bbHh bbHh
Bbhh Bbhh bbhh bbhh
BbHh BbHh bbHh bbHh
Bbhh Bbhh bbhh bbhh
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Extra tips

• When determining the probability of events
• If the problem states and then multiply the
  chances for each
• Chance of heads and heads ½ x ½ ¼ or 25
• If the problem states or then add the chances
  for each
• Chance of heads or tails ½ ½ 1 or 100
• As you work the problems write in your own extra
  tips