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AP Biology — Unit 5 — Mendelian Inheritance — Drill 18

Drill 18 ·

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About This Drill

AP Biology — Unit 5 — Mendelian Inheritance — Drill 18 is a practice drill. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.

Practice applying Mendel's laws to predict inheritance patterns with this AP Biology drill. You will use Punnett squares to calculate genotype and phenotype ratios, distinguish the law of segregation from the law of independent assortment, and analyze crosses involving both monohybrid and dihybrid scenarios.

Passage

Gregor Mendel's experiments with pea plants established the foundational principles of inheritance. Mendel's first law, the Law of Segregation, states that each organism carries two alleles for each trait, and these alleles separate during gamete formation so each gamete carries only one allele per gene. Mendel's second law, the Law of Independent Assortment, states that alleles of different genes assort into gametes independently of one another, provided the genes are located on different chromosomes. In standard Mendelian genetics, one allele is dominant (uppercase, e.g., A) and the other is recessive (lowercase, e.g., a). Dominant alleles mask recessive alleles in heterozygous genotype (Aa). Pea Plant Cross Data A genetics student crossed two pea plants heterozygous for seed color (Y = yellow, y = green) and seed shape (R = round, r = wrinkled). Cross: YyRr x YyRr Expected phenotypic ratio (dihybrid): 9 yellow round : 3 yellow wrinkled : 3 green round : 1 green wrinkled The student grew 320 offspring:
  • Yellow round: 181
  • Yellow wrinkled: 57
  • Green round: 62
  • Green wrinkled: 20
  • Total: 320

Questions in This Drill

  1. In the cross YyRr x YyRr, how many different genotypes are possible in the offspring, and what fraction of offspring is expected to be homozygous dominant for both traits (YYRR)?
  2. The student's observed results are 181:57:62:20. The expected ratio is 9:3:3:1. Do these data support Mendel's laws, and what approach helps evaluate this statistically?
  3. A true-breeding YYRR plant is crossed with a true-breeding yyrr plant. All F1 offspring are YyRr. The F1 plants self-fertilize. Which of the following correctly describes the F2 generation?
  4. A student proposes that seed color (Y gene) and seed shape (R gene) are located on the same chromosome. Which observation would be most inconsistent with this proposal, assuming no crossing over?
  5. A cross between two pea plants produces 75 yellow and 25 green offspring. Which of the following best identifies the most likely parental genotypes?