PLSC 631 - Intermediate Genetics
Genetic Linkage Quiz
1. A homozygous curly fly (cu) is crossed with a homozygous striped fly (sr). The F1 females are test crossed to a curly, striped fly. The following data was obtained: | Phenotype | No. Observed |
|---|
| Curly | 450 |
| Striped | 430 |
| Curly, striped | 55 |
| Wild type | 65 |
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 flies 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. In tomato, the gene controlling normal (O) or oblate (o) fruit shape is linked to the gene for simple (S) or compound (s) inflorescence. The inflorescence gene in turn is linked to a gene that controls few (Lc) or many (lc) locules inside the fruit. Create a data set of 1000 progeney from a three-point testcross that reflects this linkage data. The data should also have a crossover interference value of less than one and greater than zero.
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.