REPRODUCTION IN ANIMALS | TYPES OF REPRODUCTION
What is Reproduction in Animals? Reproduction is the ability to produce new individuals of ones own kind or reproduction is the biological process which leads to the production of the new individuals. Let’s discuss in detail reproduction in animals are as under;
TYPES OF REPRODUCTION IN ANIMALS
There are two types of reproduction in animals:
- Asexual Reproduction
- Sexual Reproduction
Asexual reproduction is a smaller amount common in animals as compared to reproduction in plants. Binary fission, multiple fission, budding, parthenogenesis, tissue culturing, biological research and identical twins are the common asexual methods of reproduction.
1. BINARY FISSION
It is a type of asexual reproduction in which parent organism merely divides into two daughter organisms. e.g.,
i. Amoeba merely divides through mitotic method to provide rise to two new individuals which grow and then redivide.
ii Paramecium conjointly divides mitotically to provide rise to two individuals.
2. MULTIPLE FISSION
It is a kind of asexual reproduction in which the first nucleus divides into several nuclei, then cytoplasm gathers around each nucleus to create daughter cells. Thus several cells are obtained from one cell. e.g. Amoeba.
Amoeba under unfavourable conditions withdraws its pseudopodia and secretes a cyst around itself. At the advent of favourable conditions, the nucleus divides into a number of nuclei. A piece of cytoplasm gathers around each daughter nucleus to form a daughter amoeba. The cyst’ is dissolved and the daughter amoebae become free.
Budding is a type of asexual reproduction in Which new organism produced as an outgrowth, called bud, on the body of the parent. The bud separates and gives rise to a new individual e.g., Hydra.
Some platyhelminthes, like Planaria, reproduce asexually through the division of their bodies into two halves. Each half then becomes complete animal by regenerating the lost part. There are groups of annelid worms that live in fresh water. They regularly reproduce by dividing into two pieces. The anterior piece regenerates a new posterior part and the posterior piece regenerates a new anterior part.
Parthenogenesis is defined as the development of an egg without fertilization. Ants, bees and wasps are good examples.
Haploid parthenogenesis: In the honeybees, males (or drones) develop from unfertilized eggs. The queen bee, though carrying male gametes from a male, has the ability to lay eggs that have not been fertilized. The sperms she receives from a drone- bee are stored in a pouch closed off by a valve. The eggs may be fertilized or may not be fertilized from the stored sperms. The haploid egg develops into haploid offspring and it is called haploid parthenogenesis.
Diploid parthenogenesis: In some cases e.g., in aphids, diploid parthenogenesis may occur. In this process, the egg-producing cells of the female undergo a modified form of meiosis involving total non-disjunction Of the chromosomes thus retaining the diploid number. Egg (diploid) into young females.
Advantage: Parthenogenezis has the advantage of accelerating the normal reproductive rate.
6. TISSUE CULTURING AND CLONING
Tissue culturing in tissue culturing technique in plants, cambium tissue excised (removed) from plants could be stimulated by the addition of nutrients, cytökinins, and IAA (Indole Acetic Acid) These cells show continued growth and differentiate into a new plant, genetically identical to their parents. Tissue culture is now widely used for the rapid propagation of desired varieties or for varieties difficult to propagate by cuttings. Similar techniques have been developed for the tissue culture of animal cells.
Organisms produced from a single cell by sub-culturing (Cloning) are called clones and phenomenon is called cloning. In animals and especially among vertebrates, a nucleus from the somatic cell is removed and introduced into an egg cell, whose own nucleus has been destroyed by ultra violet radiation. The egg with transplanted diploid somatic cell nucleus develops into an organism, genetically identical to the parent who has contributed the nucleus.
ADVANTAGES OF CLONING
i) Production of desirable animals: The cloning of desirable animals such as prize bulls, race horses etc. might be as useful as cloning of useful varieties of plants. However, the application of the technique to humans would be open to serious moral questions. Theoretically, any number of genetically identical copies of the same man or woman might be made.
ii) Quantitative study of various substances: The use of cloned cells allows the quantitative study of the action of hormone* drugs and antibodies to be made on cells. Such a technique is a useful substitute for investigating the effect of drugs, cosmetics and Pharmaceutical products on animal cells without. exposing laboratory animals to these chemicals.
iii) Identical offspring; Cloning has the advantage that all offspring behave similarly.
DISADVANTAGES OF CLONING
i) Environmental hazard: Offspring produced by cloning should have an environmental hazard, as they develop (like an out break of a disease) no resistant strains are present to lessen the impact.
ii) Clone development not fully known: The degree to which environment influences clone development is not fully known and any cloned cell would have to go through all the phases of development once again including embryo, foetus, baby and child hood (in case of human beings).
7. IDENTICAL TWINS
In higher vertebrates including man, zygote after fertilization undergoes cleavage (cell division by mitosis). When an embryo is at two celled stage, the two blastomeres, instead of remaining together, may separate. arid behave as two independent zygotes, each giving rise to a new individual. Both the organisms are products of mitosis thus they have Identical genetic make up and are called identical twins. They are produced mitotically (asexually).
Fraternal twins: In some cases, more than one egg is produced by the ferrate al! these eggs are independently fertilized forming two or more These zygotes develop into new off springs, but with different genetic combinations. Such twins or triplets are called fraternal twins or they are produced sexually.
It is the mechanism which has evolved enabling nucleic acid’ to be exchanged between organisms followed by meiosis and leading to production and union of gametes.
Meiosis and genetic recombination played a major role in the development of more complex forms of life and types of gametes, from identical gametes (isogametes) to the heterogametic stage ‘of motile male gametes (sperms or antherozoids) and non-motile female gametes (eggs or ova).
Sexual reproduction has an advantage over asexual reproduction. Both in animals and plants, an evolution of sexual reproduction also lead to the differentiation of sexes (male or female). Organisms are either having one sex (unisexual) or both the sexes (hermaphrodite or bisexual), Advance mode of sexual reproduction has unisexuaiity in animals but in plants bisexuality, in general, is retained. Despite the bisexuality (Tapeworm, earthworm etc.), cross-fertilization is ensured for maintaining the advantage of genetic recombination.