Sexual and Asexual Reproduction

In our environment, organisms cannot live forever and that is why the continuity of the species relies on individuals reproducing. Living organisms on earth including humans, animals, plants, fungi, and microorganisms follow the law of nature called reproduction. Reproductions in a layman’s language can be described as a means to ensure the survival of the species. There are two types of reproduction in our environment; one is asexual reproduction and another one is sexual reproduction. There are so many unicellular Organisms such as protists and bacteria as well as some plants and some animals also reproduce asexually. Those Organisms that reproduce asexually are found in stable environments to which they are very well suited. Most multicellular organisms usually reproduce sexually. In sexual reproduction, it involves male and female gametes (sperms and eggs) to form a zygote.

Both methods of reproduction, sexual and asexual, have their advantages and disadvantages. Sexual reproduction is adopted by vertebrates however simpler organisms such as amoeba reproduce through asexual reproduction. Refer to the official website of Vedantu or download the app for a detailed and comprehensive explanation.

Asexual Reproduction 

In asexual reproduction, organisms reproduce by mitotic divisions producing offspring that are identical to their parents- clones. It is a form of reproduction where gamete fusion or change in chromosome number is not required. In this form of reproduction, there are no sex cells or fertilization. Therefore, this process requires the involvement of a single parent. In multicellular Organisms, an ordinary body cell undergoes cellular division and as a result, a new individual will arise.

Some methods of sexual reproduction are as follow: -

• Binary fission such as in Amoeba, bacteria

• Fragmentation such as in Planaria 

• Spore formation such as in ferns

• Budding such as in hydra 

• Vegetative propagation such as in the onion

A common feature of all these methods is that the offspring in asexual reproduction is a direct clone of the parent. The aim of the process of reproduction is to propagate one’s own genes. Evolutionarily speaking, this form of reproduction suits these species better. Asexual reproduction is a quick and simple process for simpler organisms. In this type of reproduction, the genes of parents do not get diluted by those of other individuals. This method of reproduction also helps to produce twice as fast as one that reproduces sexually. 

Let us learn about these methods in detail.

Types of Asexual Reproduction in Animals

There are several ways by which Organisms may reproduce asexually 

Fission Reproduction

• In fission reproduction, a single cell is divided into two equal halves.

• Fission is one of the common ways of asexual reproduction among unicellular Organisms such as bacteria. 

• After the mitotic division of the nucleus, fission occurs in which a new organism is formed by splitting the parent cell into two equally sized daughter cells. 

• It occurs when the environmental conditions are good, such as plenty of food, the right temperature, water, etc. Fission is a very effective way of producing many offspring. Example - Amoeba, Euglena 

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Asexual Budding 

• Except for the division of cytoplasm which is not equal, Budding is a little bit similar to fission.

• The new individuals arise from a bud or an outgrown from the parent.

• In some small multicellular animals, this type of asexual reproduction is observed.

Example - In yeasts, the cell does not divide equally into two halves; instead, there is a large parental cell and a smaller daughter cell.

Budding of Hydra

Many hydrae reproduce asexually by producing buds in the body wall. Budding in hydra occurs when they are well-fed which results in a new bud or sub bud formation. 

On a specific side, the repeated cell division leads to the development of bud as an outgrowth. The development of buds occurs when it is fully matured. After maturation, it detaches from the main body and becomes a new independent individual.

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Fragmentation

• In some multicellular organisms, Fragmentation occurs. In this mode of reproduction, a new organism is formed by each part of the organism which is broken or split into two or more parts. 

• This fragmentation reproduction is common in marine worms, starfish (echinoderms).

Parthenogenesis

Parthenogenesis is considered one of the main types of asexual reproduction where the female eggs are developed without fertilization. Pathogenesis is observed to occur naturally in invertebrates, along with some amphibians, fishes, reptiles as well.

Asexual Reproduction in Plants

Fragmentation

There are some green plants that are sophisticated in this asexual reproduction. Offspring may be produced by runners, bulbs, tubers, or rhizomes.

Spore Formation

• Mostly, Fungi develop the spores. These spores are contained within a structure that is popularly known as sporangium.

• The spores are formed by the budding. Example - Ferns

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Vegetative Reproduction

• There are some plants, which are capable of vegetative reproduction. The vegetative reproduction is the system to separate parts of one plant and to form a new independent plant.

• Vegetative reproduction may arise from many parts of plants including the underground stems and the leaves.

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Parthenogenesis

In some plants, fruits are developed from the ovary without fertilization. This type of fruit is called parthenocarpy and process formation of fruit is called pathogenesis.

Sexual Reproduction

Sexual reproduction involves two individuals and the combination of their reproductive cells from two individuals to form a third unique offspring. While reproducing sexually, the offspring produces with a different combination of genes. If one compares sexual and asexual reproduction, it will show that the method of sexual reproduction is more complex in nature. Involvement of gametes—that consist of half the number of chromosomes compared to all other cells in the organism, in sexual reproduction. Gametes are produced by a process called meiosis which generates haploid cells from diploid cells. This is when crossing over and recombination of genes. Switching from one chromosome to another ensures that genes will remain active in a given population. The period of gestation is also an important part of sexual reproduction. This is the time when the foetus gradually develops inside the mother’s womb.

The cells of multicellular organisms are divided into two broad categories, and these are 

1. Somatic Cells 

Somatic cells are all cells of the body with the exception of the germs cells.

2. Germ Cells

Germ cells are the cells that give rise to gametes.  The gametes are cells that combine in sexual reproduction to form a new organism.

Process of Sexual Reproduction

• The process of Sexual Reproduction is mitotic divisions of germ cells that produce haploid gametes (ova and sperm).

• The sperm and ova meet with each other to form a diploid (two sets of chromosomes) zygote (single cell). 

• Then zygote divides by mitotic divisions.

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Sexual Reproduction in Animals 

• The reproductive system is made of the primary and secondary sex organs.

• In animals, primary sex organs that produce the gametes include ovaries in females and testes in the male.

• The secondary sex organs contain various glands, ducts, and chambers which provide storage and play important roles in the development of gametes and give protection to the primary sex organ.