1. **Problem:** Analyze how crossing over is related to variation. Crossing over is the process during meiosis where homologous chromosomes exchange segments. This exchange creates new combinations of alleles, increasing genetic variation in offspring. 2. **Problem:** Suppose genes C and D are linked on one chromosome and genes c and d are linked on another chromosome. Assuming no crossing over, sketch daughter cells from meiosis showing chromosomes and gene positions. Since no crossing over occurs, daughter cells will inherit parental chromosomes intact: - One daughter cell gets chromosome with genes C and D. - Another daughter cell gets chromosome with genes c and d. 3. **Problem:** Describe how polyploidy is used in agriculture. Polyploidy is used to create plants with increased size, vigor, and sometimes seedlessness. For example, many fruits like seedless watermelons are polyploid. 4. **Problem:** Construct a chromosome map for genes A, B, C, and D using crossing over data: Given distances (in percent recombination): - A to D = 25% - A to B = 30% - C to D = 15% - B to D = 5% - B to C = 20% **Step 1:** Identify the closest pair: B to D = 5% **Step 2:** Place B and D close together: $$B \quad 5\% \quad D$$ **Step 3:** Use other distances to place A and C: - A to D = 25%, A to B = 30% (A is farther from B and D) - C to D = 15%, B to C = 20% **Step 4:** Since C to D is 15% and B to D is 5%, C is farther from D than B is. **Step 5:** Arrange genes on a line to minimize discrepancies: $$A \quad 25\% \quad D \quad 5\% \quad B \quad 20\% \quad C$$ Check distances: - A to B = 30% (A to D 25% + D to B 5% = 30%) correct - B to C = 20% correct - C to D = 15% (D to B 5% + B to C 20% = 25%, discrepancy suggests C is on opposite side) Try placing C on the other side of D: $$A \quad 25\% \quad D \quad 15\% \quad C \quad 20\% \quad B$$ Check B to D: - B to D = 5% given, but here B is 20% from C and C is 15% from D, so B to D would be 35%, which is too large. Try placing C between B and D: $$A \quad 25\% \quad D \quad 15\% \quad C \quad 20\% \quad B$$ This conflicts with B to D = 5%. **Final map:** $$A \quad 25\% \quad D \quad 5\% \quad B \quad 20\% \quad C$$ 5. **Problem:** Evaluate the advantage of polyploidy to a plant breeder. Polyploidy can increase genetic diversity, improve traits like size and stress resistance, and create seedless varieties, which are valuable in breeding programs.