AP Biology Questions on Calculating Recombination Frequency

📚 Quick Study Guide

• 🧬 Recombination: The process where homologous chromosomes exchange genetic material during meiosis.
• 📍 Linked Genes: Genes located close together on the same chromosome tend to be inherited together.
• 🚧 Recombination Frequency (RF): The percentage of offspring that show recombinant phenotypes. It indicates the distance between two genes on a chromosome.
• 🔢 Formula: $RF = \frac{\text{Number of Recombinant Offspring}}{\text{Total Number of Offspring}} \times 100$
• 📏 Map Units/Centimorgans (cM): 1% recombination frequency is equal to 1 map unit (or 1 centimorgan).
• 💡 Maximum RF: The maximum recombination frequency is 50%, as genes far apart on the same chromosome behave as if they are on different chromosomes (independent assortment).
• 📝 Calculating Gene Order: Recombination frequencies can be used to determine the order of genes on a chromosome. The largest RF is between the two most distant genes.

🧪 Practice Quiz

1. A cross between two parents yields the following offspring: AB = 420, ab = 410, Ab = 85, aB = 85. What is the recombination frequency?
   1. 17%
   2. 8.5%
   3. 41%
   4. 83%
2. Two genes, X and Y, are linked. The recombination frequency between them is 20%. If a double heterozygote (XY/xy) is crossed to a homozygous recessive (xy/xy), what percentage of the offspring will have the XY phenotype?
   1. 10%
   2. 20%
   3. 40%
   4. 80%
3. In a testcross, the parental phenotypes are observed in 800 offspring, while recombinant phenotypes are observed in 200 offspring. What is the recombination frequency between the two genes?
   1. 20%
   2. 25%
   3. 40%
   4. 80%
4. Genes A and B are 10 map units apart. If an AB/ab individual is testcrossed, what percentage of the progeny will be Ab/ab?
   1. 5%
   2. 10%
   3. 45%
   4. 90%
5. If the recombination frequency between genes C and D is 3%, and between genes D and E is 8%, and between C and E is 5%, what is the most likely order of these genes?
   1. C-D-E
   2. C-E-D
   3. D-C-E
   4. E-C-D
6. A plant with genotype AaBb is testcrossed to a plant with genotype aabb. The offspring genotypes are: AaBb (40%), Aabb (10%), aaBb (10%), aabb (40%). What is the recombination frequency between genes A and B?
   1. 10%
   2. 20%
   3. 40%
   4. 80%
7. Two genes, P and Q, are located on the same chromosome. The parental combinations are PQ = 450 and pq = 450. The recombinant combinations are Pq = 50 and pQ = 50. What is the recombination frequency?
   1. 5%
   2. 10%
   3. 11%
   4. 20%