Quiz 43: Animal Development
The Danio rerio (zebra fish) is a tropical freshwater fish which is important vertebrate model organism in scientific research. The zebra fish is most common and useful model organism for studies of vertebrate development and their gene function which has genomic and developmental information. The genome of zebra fish was completely sequenced and it has well developmental characters and easily observable behaviours. So, the zebra fish possesses many advantage characters for researchers. In embryonic development, it shows the large and transparent embryos and able to develop outside their mother. It has regeneration capacity also. So, researchers expect the early development of this fish to yield useful information about human development.
Compared to an asexual reproducer, a male or female animal that reproduces sexually has spent more and biologically. Sexual reproduction will takes more time and more energy. Sexual reproduction is mostly biparental, involves meiosis, gamete formation and usually fertilization also, introduces genetic variation in the offsprings; and plays a key role in evolution of species. Organisms reproduces sexually has fewer of its genes in the next generation because genetic recombination takes place causing variations in offsprings. These offsprings produced adapt better to the changing environmental conditions. A sexual reproducer cannot produce variations because genetic recombination not involved. Variations may rarely be seen due to mutation. Hence, the correct option is D.
The photograph is Blastula of an early embryonic development stage of a Lytechinus (sea urchin). Because, the photograph shows small cluster of cells and are surrounded by single epithelial layer which enveloping a blastocoel which is called as blastula. The sea urchin blastula is surrounded by a protective fertilization envelope.