Question

In metagenesis of cnidarians like Obelia, the polyps and medusae are respectively _____________
A) N and 2N
B) 2N and N
C) 2N and 2N
D) N and N

Answer 1

Hint: Metagenesis is a result of polymorphism. Polymorphism is the phenomenon in which there is a division of labour among individuals. It means that different functions are performed by different individuals, an alternative to being performed by parts of the same organism.

Complete answer:
In metagenesis, the different individuals are genetically the same. They only differ in morphology and functionality. Both forms are complementary to each other. They rely on each other for the completion of the life cycle and other activities.

The polyps of Obelia reproduce asexually to produce sexual, free-swimming medusa through budding. The medusa reproduces sexually and produces new polyps. This means that a diploid asexual polyp’s phase alternates with a sexual medusoid phase, which is also diploid.

In the alternation of generation, the two forms are genotypically different. One will be haploid and the other will be diploid. The diploid form can be produced either by sexual or asexual methods. However, the haploid form can only be produced by the asexual method.

So, the correct answer is option ‘C’ i.e, 2N and 2N.

Additional information: Polymorphism is defined as the coexistence of two or more distinct forms independent of sex. They coexist in the same locality. They are not connected by intermediate gradations; however, they are produced from the same parents. Metagenesis, on the other hand, is the production of sexual and asexual organisms in alternate generations. In simple terms, polymorphism is the ability to assume various forms or shapes.

Note: Some sources consider metagenesis and alternation of generation to be the same thing. In the case of alternation of generation, the diploid form alters with the haploid form. Both forms are capable of existing in their life without the other form. They are not complementary to each other to complete their life cycle.