PLSC 631 - Intermediate Genetics
Genetic Linkage Quiz
1. Wild type sweetpea plants have red flowers and long pollen grains. These two traits are dominant to white flowers and short pollen grains, respectively. A wild type plant was crossed to a plant with white flowers and short pollen grains. The F1 was test crossed to a white flowered, small pollen grain plant, and the following results were obtained: | Phenotype | No. Observed |
|---|
| Wild type | 228 |
| Short pollen grains | 19 |
| White flowers | 21 |
| White flowers, short pollen grains | 232 |
a. Are these genes linked? If so, what is the distance between them? b. Is the F1 in coupling or repulsion phase? C.If the F1 plants were intermated instead of testcrossed, what would be the frequency of each of the four phenotypic classes. (Hint: You will need to use your results from "a" to solve this problem.)
2. The following three recessive markers are known for tomato: d, dwarf height; p, peach fruit; and m mottled leaves. A trihybrid of unknown origin was tested crossed and produced the following distribution of offspring.
| Phenotype | Observed |
|---|
| Peach | 402 |
| Dwarf, mottled | 444 |
| Dwarf | 62 |
| Mottled, peach | 54 |
| wild type | 17 |
| Dwarf, mottled, peach | 19 |
| Dwarf, peach | 1 |
| Mottled | 3 |
a. Are the three genes linked?, If so, what is the distance between them. b. What is the coupling-repulsion arrangement in the original trihybrid? c. Is there any crossover interference? If so, how much?
3. In human, the A, B, O system (A, B, O alleles) is linked to the aldolase-B locus (al, al+ alleles), a gene that functions in the liver. The recessive aldolase deficiency results in fructose intolerance. A 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 type A and intolerant to fructose. Determine the map distance between the two genes using the Lod score method. (Hint: Remember, you will need to first make an estimate of the linkage distance based on the pedigree and then calculate a series of Lod scores using different recombination frequencies to determine the best distance estimates.)
4. The following is a map of a portion of chromosome nine of corn.
| Map Position | Gene |
|---|
35 | Shrunken 1 (sh1) |
38 | Bronze 1 (bz1) |
56 | Waxy 1 (wx1) |
124 | White Cap 1wc1) |
a. If plants heterozygous for bronze 1 and white cap 1 are mated, what phenotypic ratio would you expect in the progeny.
b. A true-breeding shrunken 1, waxy 1 plant is crossed with a true-breeding bronze 1 plant. An F1 female is testcrossed to a shrunken 1, bronze 1, waxy 1 plant. Predict the progeny and their frequencies for this cross.