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AP Biology — Unit 5 — Pedigrees & Genetic Analysis — Drill 21

Drill 21 ·

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About This Drill

AP Biology — Unit 5 — Pedigrees & Genetic Analysis — Drill 21 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 reading and interpreting pedigrees to determine inheritance patterns with this AP Biology drill. You will identify autosomal vs. X-linked patterns, distinguish dominant from recessive inheritance, determine carrier genotypes, and calculate the probability that future offspring will be affected by a genetic condition.

Passage

A pedigree traces inheritance of a trait across multiple generations. Standard symbols: squares = males, circles = females; filled symbols = affected individuals; horizontal lines between individuals = mating; vertical lines = offspring. Key Patterns: Autosomal Recessive: Unaffected parents can have affected children; affects males and females equally; trait often skips generations; affected individuals are homozygous recessive (aa). Autosomal Dominant: At least one parent of an affected child is usually affected; trait appears every generation; affects males and females equally. X-Linked Recessive: Affects more males than females; carrier females pass trait to sons; affected fathers cannot pass to sons (daughters of affected father are carriers); trait often skips generations through female carriers. Recombination Frequency: Genes on the same chromosome can be separated by crossing over during meiosis I. Recombination frequency = (recombinant offspring / total offspring) x 100%. Genes with recombination frequency close to 50% behave as if unlinked. Genes with recombination frequency below 50% are linked. Pedigree for Analysis: Generation I: Unaffected father (I-1) x Unaffected mother (I-2) have four children. Generation II: Son II-1 (affected), Son II-2 (unaffected), Daughter II-3 (unaffected), Daughter II-4 (affected). Generation III: II-2 x unaffected female (II-5) have Son III-1 (affected) and Daughter III-2 (unaffected). Both sexes are affected in roughly equal proportions in the pedigree.

Questions in This Drill

  1. In the pedigree, two unaffected parents (I-1 and I-2) have an affected son (II-1) and an affected daughter (II-4). Which inheritance pattern is most consistent with these observations?
  2. If the condition is autosomal recessive, what are the most likely genotypes of the unaffected parents (I-1 and I-2)?
  3. The unaffected son II-2 (both parents are Aa carriers) marries an unaffected woman and has an affected son (III-1). Before knowing about his affected son, what was the probability that II-2 is a carrier (genotype Aa), given that he is unaffected?
  4. A geneticist analyzes two genes in fruit flies on the same chromosome. A testcross (AaBb x aabb) produces 400 offspring: 170 AaBb, 170 aabb, 30 Aabb, and 30 aaBb. What is the recombination frequency between Gene A and Gene B?
  5. A woman is a confirmed carrier (Aa) of an autosomal recessive condition. Her partner is unaffected; his mother was a carrier (Aa) and his father was homozygous dominant (AA). What is the probability their first child will be affected (aa)?