Question

Because B. rapa is an annual plant, the one rosette individual dies. Cyndi would like to continue her study of this mutation, but all of the offspring from her original cross were normal. There are no more plants with the rosette mutation.

What can Cyndi do to continue her investigation of rosette?

What would be the results of these "next steps"?

Answer 1

A recessive mutation exhibits its phenotype only in the homozygous condition.
A dominant mutation can exhibit its phenotype in both homozygous as well as heterozygous conditions.

To determine whether the given phenotype is due to a recessive mutation, we need to cross the mutant plant with a purebred WT plant and analyze the progeny.
If the F1 progeny exhibits the mutant phenotype, the mutation is due to a dominant allele.
If the F1 progeny exhibits the WT phenotype, the mutation is due to a recessive allele.

Since the F1 exhibits the WT phenotype, we can conclude that the phenotype is due to a recessive mutation.
The next step is to determine whether the phenotype is due to a mutation in a single gene or multiple genes.

To identify that, allow the F1 plants to self-fertilization and analyze the F2 progeny.
If the F2 progeny exhibits the phenotypic ratio of 3:1 (3 WT and 1 mutant), the phenotype is due to a mutation in a single gene.
If the F2 progeny exhibits the phenotypic ratio of 9:3:3:1 (1/16 mutant), the phenotype is due to mutations in two genes.