Question

You are interested in the genetics of flower colour determination in daffodils. The wild type has yellow flowers. In a genetic screen, you isolate two mutants with white flowers. Suggest and explain experimental strategies to answer the following questions:

i) Is each of the mutants defective in a single or multiple genes?

ii) Assuming that the mutants are defective in a single gene, are the mutations recessive or dominant to the wild type gene?

iii) Assuming both mutants are affected in a single recessive gene, are the same or different genes affected in the two mutants?

Answer 1

i) Each of the mutants can be defective in either single or multiple genes. In order to study that one way can be comparing the genes that are present in the wild type and the mutant flowers. The genes that are responsible for the coloration of the daffodils work individually or in combination. Complementation tests can be done to test whether the mutations in the color providing genes affect each other or only one single gene is involved.

ii) To check if the mutations are recessive or dominant, test cross can be done to check whether the the wild type gene is heterozygous or homozygous. Depending on that, the recessiveness or the dominance can be determined.

iii) The two mutants may or may not have the mutations in the same or different genes. To check if the mutations are same or different in the two mutant flowers, PCR of the mutated genes that have been studied earlier can be done and then the intronic and exonic sequences can be studied to see which has a defective presence that would give an extra band on the gel.