What is sexual Reproduction | Defination | Advantages

What is Reproduction?
Reproduction is a life process which enables an organism to reproduce its own offspring. Thus, they continue their species without extinction. Reproduction can take place by the participation of a single parent or two parents.  Based on this, we can classify reproduction into two types.

Asexual reproduction: A type of reproduction where a single parent is divided by itself and reproduce its offspring.

Sexual reproduction: A process where two parents participate in producing their offspring. Let discuss About Sexual Reproduction.

Sexual Reproduction :
Sexual reproduction is defined as the mode of reproduction which involves in fusion of two compatible gametes or sex cells ( male and female gametes). All organisms reach to the maturity in their life before they can reproduce sexually. In plants, the end of juvenile or vegetative phase marks the begining of the reproductive phase and can be seen easily in the higher plants at the time of flowering.  Sexual reproduction involves two major events viz. meiosis and fusion of gametes to form diploid zygote and the production of genetically dissimilar offsprings. Sexual reproduction is characterised by fusion of the male and female gametes (fertilization), the formation of zygote and embryogenesis.

All orgmisms have to  reach a certain stage of growth and maturity in their life. before they con  reproduce sexually. That  period of growth is called  tho Juvenile phase. It is known as vegetative phase in plants. This phase is variable duration in different organisms.

There are concomitant  changes in the body (like  slowing of metabolism.  etc.) during this last phase of life span. Old  age ultimately leads to death. In both plants and  animals hormones are  responsible for the transitions between the  three phases. Interaction between hormones and certain environmental factors regulate the  reproductive processes and the associated behavioural expressions of organisms.

Events in sexual reproduction : After attainment of maturity. all sexually reproducing organisms exhibit events and processes that have remarkable fundamental similarity.  even though the structures associated with sexual reproduction are indeed very different. The  events of sexual  reproduction though  elaborate and complex.  follow a regular  sequence. Sexual reproduction is characterised by the fusion (or fertilisation)  of the male and female gametes. the formation of zygote  and embryogenesis.

Sequential events that occur in sexual reproduction are grouped into three distinct stages are
1. Pre-fertilization,
2. Fertilization and the
3. Post-fertilization.

1. Pre-fertilisation  Events : These include  all the events of sexual reproduction prior to the fusion of gametes. The two main pre-fertilisation events are gametogenesis and gamete transfer.

a. Gametogenesis : gametogenesis refers to the process of formation of the two types of  gametes-male and  female. Gametes are  haploid cells. In some  algae the two gametes  are so similar in  appearance that it is not possible to categorise them into male and  female gametes.

b. Gamete Transfer : After Formation of male and  female gametes must  be physically brought  together to facilitate  fusion (fertiliSation).Fertilization is the fusion of male and female gametes.

2. Fertilisation :

The most vital event of sexual reproduction is perhaps the fusion of  gametes. This process  called syngamy results  in the formation of a  diploid zygote. Th  term fertilisation is also  often  used for this process.  The terms syngamy and  fertilisation are  frequently used though  ,  interchangeably.

In most aquatic organisms, such as a  majority of algae and  fishes as well as amphibians, syngamy occurs in the  external medium (water), i.e.,  outside the body of the organism. This type of gametic fusion is called  external fertilisation.

In many terrestrial organisms, belonging to fungi, higher animals such as reptiles birds,  mammals and in a  majority of plants  (bryophytes, pteridophytes,  gymnosperms and  angiosperms), syngamy occurs inside the body of an organisms is called internal fertilization.

3. Post-fertilisation  Events : Elents in sexual  reproduction after the  formation of zygote are  called post-fertilization  events.  Like zygote and embryogenesis.

a. Zygote : Zygote Formation of the  diploid zygote is  universal in all sexually  reproducing organisms.  In  organisms with  external fertilisation.  zygote is formed in the external medium (usually water). whereas in those fertilisation, zygote is  formed inside the body of the orgonism.

b. Embryogenesis : Embryogenesis refers to  the process  of formation and development of embryo  from the zygote. During embryogenesis zygote undergoes cell division (mitosis) and cell differentiation. cell division increase the number of cells in the developing embryo while cell differentiation helps  groups of cells to undergo certain specialized modifications to forms tissue, organs, organ system and complete organisms.

Hermaphroditism :
Hermaphroditism occurs in animals where one individual has both male and female reproductive parts. Invertebrates, such as earthworms, slugs, tapeworms and snails, are often hermaphroditic. Hermaphrodites may self-fertilize or may mate with another of their species, fertilizing each other and both producing offspring. Self fertilization is common in animals that have limited mobility or are not motile, such as barnacles and clams.

The advantages of sexual reproduction:
1. It produces genetic variation in the offspring.
2. The species can adapt to new environments due to variation, which gives them a survival advantage.
3. A disease is less likely to affect all the individuals in a population.
4. One of the most important advantages of sexual reproduction is that it results in genetic variation among offsprings.
5. Genetic recombination is another advantage of sexual reproduction.