Wednesday, January 14, 2009

Asexual Reproduction in Animals

In animals the asexual reproduction is limited to unicellular and lower forms organisms. Following are the different methods of asexual reproductions.

1) Binary fission:
The parent cell divides into two or more daughter cells by a cleavage of the protoplast after the nuclear division. Normally two identical cells are formed. Therefore, it is known as binary fission. It is usually observed in organisms such as plasmodium, paramecium, amoeba, etc. When the parent cell is divided into a number of progenies it is called multiple fission. First, the nucleus undergoes repeated division, which is followed by cytoplasmic division into a number of daughter cells. The cell undergoing multiple fission is called schizont and the process is known as schizogamy.

2) Budding :
Here, offspring develops as a growth on the body of the parent. In some species (e.g., jellyfishes) the buds break away and take up an independent existence. In others (e.g., corals) the buds remain attached to the parent and the process results in colonies of animals. Budding is also common among parasitic animals such as tapeworms.

3) Fragmentation
In certain tiny worms, as they grow to full size, they spontaneously break up into eight or nine pieces. Each of these fragments develops into a mature worm and the process is repeated.

4) Parthenogenesis:
In parthenogenesis ("virgin birth"), the female produces eggs, but these develop into young without ever being fertilized. Parthenogenesis occurs in some fishes, several kinds of insects, and a few species of lizards. In a few species it is the only method of reproduction, but more commonly animals turn to parthenogenesis only at certain times. For example, aphids use parthenogenesis in the spring when they find themselves with ample food. Reproduction by parthenogenesis is more rapid than sexual reproduction, and the use of this mode of asexual reproduction permits the animals to quickly exploit the available resources.

Parthenogenesis is forced on some species of wasps when they become infected with bacteria such as the genus Wolbachia. In these wasps (as in honeybees), fertilized eggs (diploid) become females; unfertilized (haploid) eggs become males. However, in Wolbachia-infected females, all their eggs undergo endoreplication producing diploid eggs that develop into females without fertilization; that is, by parthenogenesis. Treating the wasps with an antibiotic kills off the bacteria and "cures" the parthenogenesis.

Tags: Asexual Reproduction, Bio Technology, Bio Genetics

Related Posts by Categories