What is Sexual Reproduction | Definition | Advantages

Reproduction is a life process that 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.

What is Sexual Reproduction | Definition |  Advantages

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

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

What is Sexual Reproduction

Sexual reproduction is defined as the mode of reproduction that involves the infusion of two compatible gametes or sex cells ( male and female gametes). All organisms react to maturity in their life before they can reproduce sexually. In plants, the end of the juvenile or vegetative phase marks the beginning 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 a diploid zygote and the production of genetically dissimilar offspring. Sexual reproduction is characterized by a fusion of the male and female gametes (fertilization), the formation of a zygote, and embryogenesis.

All organisms have to reach a certain stage of growth and maturity in their life. before they can reproduce sexually. That period of growth is called the Juvenile phase. It is known as a vegetative phase in plants. This phase is the 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 regulates the reproductive processes and the associated behavioral expressions of organisms.

Types of Sexual Reproduction

There are different types of Sexual Reproduction that have evolved over time.

  • Conjugation: This is the simplest form where specialized gametes aren’t formed, but ordinary cells merge. We see this in ciliates and spirogyra.
  • Isogamy: Here, morphologically identical gametes fuse. An example is Chlamydomonas.
  • Heterogamy: This process involves two motile gametes merging, with one significantly larger than the other. It’s found in some algae species and the malarial plasmodium.
  • Oogamy: This is the most common form, where one gamete is a large, immobile egg, and the other is a small, motile sperm. Eggs are usually the female gametes, and sperm are the male gametes. This setup allows the egg to accumulate nutrients for future complex multicellular organism formation, while the sperm’s mobility increases the chances of fertilization. In some organisms without motile cells like red algae, seed plants, and roundworms, both gametes are immobile, called sperm. Their connection is facilitated by environmental movement or special organs of the parent organisms. Typically, gametes are produced in specialized organs called gonads in complex multicellular organisms.

Events in Sexual Reproduction

After attainment of maturity. all sexually reproducing organisms exhibit events and processes that have a remarkable fundamental similarity.  even though the structures associated with sexual reproduction are indeed very different.

The events of sexual reproduction through elaborate and complex.  follow a regular sequence. Sexual reproduction is characterized by the fusion (or fertilization)  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 before the fusion of gametes. The two main pre-fertilization events are gametogenesis and gamete transfer.

  • 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 categorize them into male and female gametes.
  • Gamete Transfer: After the 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. The term fertilization is also often used for this process.  The terms syngamy and fertilization 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 fertilization.

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 organisms is called internal fertilization.

3. Post-fertilisation  Events

Events in sexual reproduction after the formation of the 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 fertilization.  a zygote is formed in the external medium (usually water). whereas in that fertilization, the zygote is formed inside the body of the organism.
  • b. Embryogenesis: Embryogenesis refers to the process of formation and development of an embryo from the zygote. During embryogenesis, the zygote undergoes cell division (mitosis) and cell differentiation. cell division increases 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.
What is Sexual Reproduction | Definition |  Advantages

The Advantages of Sexual Reproduction

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

What are the Advantages of Sexual Reproduction over Asexual Reproduction

AdvantagesSexual ReproductionAsexual Reproduction
Genetic DiversityIn sexual reproduction Offspring inherit a unique combination of genes from two parents, leading to greater genetic variation.In Asexual reproduction Offspring are genetically identical to the parent, resulting in limited genetic diversity.
Adaptation to Changing EnvironmentsIncreased genetic diversity allows populations to adapt to changing environmental conditions more effectively.Limited genetic variation may make populations less adaptable to changing environments.
Elimination of Harmful MutationsGenetic recombination and crossing over during meiosis can eliminate harmful mutations by producing offspring with different genetic combinations.Harmful mutations are retained in all offspring since there is no genetic recombination.
Evolutionary AdvantageSexual reproduction facilitates natural selection by providing a wider range of genetic variation for evolution to act upon.Asexual reproduction may lead to evolutionary stagnation as there is no mechanism for introducing new genetic variations.
Enhanced Immune SystemOffspring inherit a diverse set of immune system genes from both parents, potentially resulting in stronger immune responses and resistance to diseases.Offspring have limited genetic variation in their immune system genes, potentially making them more susceptible to diseases.
Masking of Recessive TraitsDominant alleles can mask the expression of harmful recessive alleles, reducing the likelihood of genetic disorders in offspring.Recessive traits are expressed in all offspring, increasing the likelihood of genetic disorders if harmful alleles are present.

Difference between Sexual and Asexual Reproduction

Asexual ReproductionSexual Reproduction
It occurs in prokaryotic microorganisms and in some eukaryotic unicellular and multicellular organisms, lower invertebrates and plantsIt occurs almost in all types of multicellular organisms including humans, animals, and higher plants.
It is uniparental.It is usually bi-parental.
Gametes are not formed.Gametes are formed.
No fertilization occurs.Fertilization takes place.
Only mitosis type of cell division occurs.Both meiosis and mitosis type of cell division occurs.
The progeny and the parent are genetically identical.The progenies will be genetically different from the parents.
Multiplication is very rapid and takes less time.Multiplication is not so rapid and takes a longer time to complete.
The number of offsprings produced may vary from two to many.The number of offsprings produced is comparatively lower.
Bacterial fission, fragmentation, spore formation, budding of hydra are different types of asexual reproduction.Syngamy, external fertilization, and conjugation are different types of sexual reproduction.
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