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About This Drill
AP Biology — Unit 5 — Meiosis & Genetic Diversity — Drill 17 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 analyzing meiosis, crossing over, and independent assortment as sources of genetic diversity with this AP Biology drill.
Passage
Meiosis is a specialized form of cell division that produces haploid gametes from diploid parent cells. Unlike mitosis, meiosis involves two sequential rounds of division -- meiosis I and meiosis II -- and introduces genetic variation through two mechanisms: crossing over and independent assortment.
During prophase I, homologous chromosomes pair along their entire length in a process called synapsis, forming bivalents. Crossing over occurs at points called chiasmata, where non-sister chromatids of homologous chromosomes exchange corresponding segments of DNA. This produces recombinant chromatids containing allele combinations not present in either parent chromosome.
During metaphase I, homologous chromosome pairs align at the metaphase plate independently of one another. The orientation of each bivalent is random, so either homolog may be pulled toward either pole during anaphase I. For an organism with n pairs of homologous chromosomes, independent assortment can produce 2^n possible combinations of homologous chromosomes in gametes.
Scenario: A diploid organism has 4 pairs of homologous chromosomes (2n = 8). A researcher tracks the inheritance of two gene loci: Gene P, located near the centromere of chromosome 1, and Gene Q, located near the telomere of chromosome 1.
Questions in This Drill
- Based on the passage, which of the following best explains why Genes P and Q are less likely to assort independently compared to two genes located on different chromosomes?
- The researcher notes that Gene Q, located near the telomere of chromosome 1, shows a higher recombination frequency with Gene P than two other genes located adjacent to each other near the centromere. Which of the following best explains this observation?
- For the organism described in the scenario (2n = 8), how many possible chromosome combinations can be produced in the gametes through independent assortment alone?
- A student argues that crossing over and independent assortment are redundant mechanisms because both produce genetic variation in gametes. Which of the following best identifies the flaw in this argument?
- The researcher discovers a mutation that eliminates chiasmata formation entirely during prophase I. Which of the following best predicts the consequence of this mutation for genetic diversity in the organism's gametes?