Reproduction

Reproduction is one of the important process by which every living organism makes a copy like itself. It is the means of multiplication and perpetuation of the species. Reproduction is not an essential life process, means it is not necessary to reproduce in order to survive, one can survive without undergoing reproduction also, yet it is a unique property of living beings.

In reproduction, a lot of energy goes waste to produce new individual, but it is essential for the survival of a species or for the continuity of life on the earth because the older individuals of each species undergo senescence and die.

Reproduction at its basic level (cellular reproduction) is involved in making similar or dissimilar body designs through the genetic material (DNA) present in the chromosomes of its nucleus. DNA is the blueprint of life. It is the source of information for making proteins. It stores all the information about the body design, building and running of the cellular machinery and functioning of the individuals. Any change in the information leads to production of different proteins, which ultimately lead to altered body designs.

Basic event in reproduction is production of DNA copies in a reproducing cell. The process is called DNA replication. Cells use chemical reactions to build copies of their DNA. When the cell divides into two, each new cell gets a copy of each DNA or chromosome along with the whole cellular apparatus.

Variation: Complete accuracy in DNA copying leads to two exactly identical cells but any error in duplication can lead to dissimilar cells or variations. 

Variations are differences in structure, physiology and other traits found in individuals of species.

If there were a population of bacteria living in temperate regions and if the water temperature were to be increased by global warming, most of these bacteria would die but the few variants resistant to heat would survive and grow further. Variation is, thus, useful for the survival of species over time.

1.0Significance of Reproduction

For maintenance of continuity of a species: Since, every organism dies after a certain age so as by the process of reproduction, new individuals are born which can replace the dead ones. 

For adding variation for evolution: By reproduction new variations are added as you can see the members of a family having variation in color, shape, size, intelligence, body capacity etc, some are better suitable than other which are selected by nature and others die and are removed. 

For maintenance of population size: By reproduction, new members are added which maintains the population size.

2.0Types of Reproduction

There are two types of reproduction in living organisms :-

1. Asexual reproduction 2. Sexual reproduction

1. Asexual reproduction: Production of offsprings by a single parent without the formation and fusion of gametes is called asexual reproduction. It is a primitive type of reproduction in which offsprings are produced by a cell or any vegetative organ of an organism.

In this type of reproduction, offsprings are genetically identical to their parents.

2. Sexual reproduction: It is a type of reproduction in which two different sex cells (gametes) take part.

The gametes often come from two different individuals called male and female, so they bring some variations in the next generations. 

All sexually reproducing organisms have two sets of chromosomes called homologous chromosomes. In such set, one set of chromosomes come from each parent. The number of chromosomes is reduced to one set by a kind of cell division called meiosis in which four cells are produced each with only one set of chromosomes, which later develops into gametes. Thus, when two such sex cells (gametes) fuses, they restore the number of chromosomes of that species.

Sexual reproduction involves following steps

a. Formation of gametes (by meiotic cell division)

b. Fusion of gametes (Formation of zygote)

c. Development of zygote to new individual

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