Question

In the prothallus of a vascular cryptogam, the antherozoids and eggs mature at different times. As a result

• A. There is no change in-success rate of fertilization.
• B. There is high degree of sterility.
• C. One can conclude that the plant is atomistic.
• D. Self fertilization is prevented.

Answer 1

The correct option is D Self fertilization is prevented.

There are several mechanisms ferns use to prevent self-fertilization and the resulting homozygosity. Intergametophytic crossing, sperm fertilizing an egg on a different gametophyte where both plants arose from separate sporophytes, occurs. This is similar to pollen from one lily landing on the stigma of another separate lily plant several meters away. Some fern gametophytes produce a pheromone called antheridiogen. This pheromone causes neighboring immature gametophytes to produce only antheridia. This allows much more sperms to be produced for possible cross-fertilization of the egg. Archegonia and antheridia mature at different rates to prevent intragametophytic selfing. One of the most interesting strategies used by ferns to prevent evolutionary stagnancy is polyploidy. Over 95% of ferns have been found to be polyploid. This results from a process known as allopolyploidy.