Practice Quiz

Praxis II Biology

Category - Biology

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You are charged with investigating inheritance of height (T) and hair color (B) in a family. Tall height and black hair are dominant phenotypes, and short height and blonde hair are recessive phenotypes. The father’s genotype is TTbb, and the mother’s genotype is ttBB. What will be the predicted ratio of inherited traits in the F2 generation?
  1. 3:1
  2. 12:4
  3. 9:3:3:1
  4. 10:3:2:1
  5. 6:8:1:1
Explanation
Answer: C, The predicted ratio of inherited traits in the F2 generation will be 9:3:3:1. The answer is readily apparent after the Punnett square is completed

Key Takeaway: This investigation is an example of a dihybrid cross. In a dihybrid cross, recessive traits can only be observed in the 2nd and following generations, as all F1 generation offspring will have a genotype of TtBb. 3 offspring will be short with black hair and 3 will be tall with black hair. One offspring will be homozygous for both recessive traits, and will be short with blonde hair. The remaining 9 offspring will be tall with black hair.
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