15. When two mutants having the same phenotype were crossed, the progeny obtained showed a wild-type phenotype. Thus the mutations are
(1) non-allelic.
(2) allelic.
(3) segregating from each other.
(4) independently assorting

Explanation

When two mutants with the same mutant phenotype produce a wild-type phenotype progeny when crossed, it indicates:

• The mutations lie in different genes (non-allelic).

• Each mutant provides a functional copy of the gene lacking in the other, so together they complement one another and restore the wild-type phenotype.

This test is known as a complementation test and is used to distinguish whether mutations are:

• Allelic (same gene): cross yields mutant offspring.

• Non-allelic (different genes): cross yields wild type offspring.

Option-wise analysis

1. Non-allelic – correct

   • Mutations in different genes complement each other, producing wild-type progeny.

   • Matches the given scenario.

2. Allelic

   • Different mutations of the same gene fail to complement; progeny show mutant phenotype. Not correct here.

3. Segregating from each other

   • Segregation pertains to inheritance patterns, not allelism; not directly related to interpretation of complementation test results.

4. Independently assorting

   • Applies to genes located on different chromosomes or far apart on the same chromosome but does not specifically describe allelism or complementation outcomes.

So, since the mutants complement and progeny are wild type, the mutations are non-allelic (option 1).