Homework Assignment - Genetic Linkage
100 points each (20 pts each)
Use complete sentences in all of your answers where appropriate. If you are stumped by a problem, explain as much as you can to get partial credit.
1. A homozygous groucho fly (gro, bristles about the eye) is crossed with a homozygous rough fly (ro, eye abnormality). The F1 females are test crossed to a groucho, rough fly. The following data was obtained.
| Phenotype | No. Observed |
|---|---|
| Groucho | 514 |
| Rough | 466 |
| Groucho, rough | 11 |
| Wild type | 9 |
a. Are these genes linked? If so,
what is the distance between them?
b. Is the F1 in coupling or repulsion phase.
2. If the F1’s in the first problem were intermated instead of testcrossed, what would the frequency of each of the four phenotypic classes. (Hint: You will need to use your results from #1 to solve this problem.)
3. The following three recessive markers are known for lab mice: h, hotfoot; o, obese; and wa, waved. A trihybrid of unknown origin was tested crossed and produced the following distribution of offspring.
| Phenotype | Observed |
|---|---|
| hotfoot, obese, waved | 357 |
| hotfoot, obese | 74 |
| waved | 66 |
| obese | 79 |
| wild type | 343 |
| hotfoot, waved | 61 |
| obese, waved | 11 |
| hotfoot | 9 |
a. Are the three genes linked?, If so, what is the distance
between them?
b. What is the coupling-repulsion arrangement among the three genes in
the original trihybrid?
c. Is there any crossover interference? If so, how much?
4. The following is a map information of a portion of chromosome three of Drosophila.
| Map Position | Gene |
|---|---|
| 19 | javelin bristles (jv) |
| 43 | thread arista (th) |
| 66 | delta veins (Dl) |
| 71 | ebony body (e) |
a. If flies heterozygous
in the coupling position for javelin and ebony eyes are mated, what phenotypic
ratio would you expect in the progeny. Why?
5. In human, the ABO blood type system (codominant alleles A, B, and O) is linked to the aldolase-B gene (alleles = al, al+), a gene that functions in the liver. Individuals homozygous recessive aldolase deficiency allele (al) express fructose intolerance. A normal man with blood type AB had a fructose intolerant type B father and a normal type AB mother. He and a woman with blood type O and fructose intolerance had ten children. Five of the children were type A and normal, three were fructose intolerant and type B, and two were typeA and intolerant to fructose.
a. Draw a pedigree for this family that includes the genotypes of the grandparents, parents, and offspring. (If you wish, you can use a diamond symbol with a number inside to denote the three phenotypes of the generation III individuals.)
b. In this pedigree, which blood type allele (A, B, O) is linked to which aldolase deficiency allele (al, al+)?
c. Estimate the recombination fraction (RF) for this pedigree. Then use this estimate to calculate the LOD value for linkage between the two genes. Finally, calculate two other LOD values using one RF smaller than your estimate and one larger than your estimate.