Last Updated on September 22, 2020 by Sagar Aryal
Asexual Reproduction Definition
Asexual reproduction is a mode of reproduction that occurs without the fusion of gametes and doesn’t involve the exchange of genetic information, resulting in offsprings identical to their parents.
- Asexual reproduction in living beings is characterized by the absence of male and female gametes and the lack of change in the number of chromosomes in the offspring.
- As no specific gametes are formed during asexual reproduction, the somatic cells act as gametes.
- The body of the organism undergoing asexual reproduction often does not have defined reproductive organs.
- Asexual reproduction is considered a more primitive mode of reproduction as it mostly occurs in primitive living beings like bacteria and fungi.
- This results in offsprings that are genetically identical to the parents and each other. These are also called clones.
- During asexual reproduction, mitosis occurs where the genetic material in the parent cell is doubled before dividing it into two equal halves.
- The absence of meiosis or genetic exchange results in a lack of diversity among the individuals of a group.
- The lack of diversity makes individuals susceptible to similar environmental and physical conditions.
- The process of asexual reproduction is rapid, which is useful for organisms whose strategy to survive is to reproduce rapidly.
- Asexual reproduction is a uni-parental process that can occur within a single organism, and thus no mates are required for the process.
- The process is also easier as it doesn’t require many resources like in the case of sexual reproduction. Some forms of asexual reproduction take place by merely cutting a part of the body which then develops to become a new organism.
- Depending on the mechanism of the process, asexual reproduction can occur in several ways; fission, budding, vegetative propagation, fragmentation, spore formation, and parthenogenesis.
- During fission, the parent cell divides into two genetically identical daughter cells and occurs mostly in unicellular organisms.
- Budding is the process of developing a new daughter organism from the parent organism in the form of a bud which eventually separates out as the daughter organism mature. This is common in some fungi.
- Vegetative propagation occurs in plants where new plants are formed from the parts of the plant without the formation of seeds or spores.
- In fragmentation, a new organism is formed as part (fragment) of the parent body separates out to form a fully grown organism.
- Some plants and algae undergo spore formation where the cells undergo meiosis to form haploid spore instead of gametes. These spores then develop into multicellular organisms without fertilization.
- Parthenogenesis is seen in plants, invertebrates, and some vertebrates where an unfertilized egg develops into a new organism without fertilization.
- Examples of asexual reproduction are observed in bacteria, most fungi, and some vertebrates like lizards.
Sexual Reproduction Definition
Sexual reproduction is a mode of reproduction involving a complex life cycle where the formation of new organisms occurs by the combination of genetic information from two different individuals of two different types (sexes).
- The process of sexual reproduction occurs by the formation of gametes with a haploid set of chromosomes.
- During the process of fertilization, these two gametes combine or fuse to form a cell with a diploid set of chromosomes.
- Sexual reproduction is common in higher organisms like multicellular animals, some fungi, and plants.
- It is absent in prokaryotes without nuclei but the process of bacterial conjugation, transformation, and transduction are similar in process to sexual reproduction.
- Sexual reproduction is characterized by the fertilization of a female gamete by a male gamete to form an offspring that is genetically different from both the parents.
- Sexual reproduction is a bi-parental process which requires two different individuals of different sex.
- The process of sexual reproduction is more complicated than asexual reproduction and has specialized parts and cells involved in the process.
- The formation of gametes with half the number of chromosomes is an important aspect of sexual reproduction.
- Reproductive cells during sexual reproduction undergo meiotic division where a diploid cell divides to form four haploid cells. These haploid cells are gametes. The male gametes are mostly motile, whereas the female gamete is immobile.
- Sexual reproduction also different from asexual reproduction in that it requires two parental cells for the offspring to form.
- The process is also comparatively slower as the production of offsprings in sexual reproduction occurs less rapidly.
- Fertilization during sexual reproduction can be either internal or external. During internal fertilization, the male and female gametes fuse inside the body of the female organism.
- In external fertilization, however, the male and female gametes fuse outside the body of the organism.
- Sexual reproduction is of two types depending on the production of male and female gametes; allogamy and autogamy.
- In allogamy, the male and female gametes come from two different organisms which are different from each other and exhibit sexual dimorphism. This process is also called cross-fertilization.
- Autogamy is different from allogamy in that the male and female gametes in such organisms come from the same individual, called a hermaphrodite. This process is also called self-fertilization.
- Besides, sexual reproduction is further divided into other two types based on the mechanism of the process; syngamy and conjugation.
- During syngamy, the nuclei of the male and female gametes fuse with each other whereas, during conjugation, the hyphae or plasmids fuse with each other to form diploid organisms.
- Sexual reproduction is essential as it increases the genetic diversity in a population that supports natural selection, improving the ability of the individual to adapt to the environmental conditions.
- Sexual reproduction is the driving force for speciation where new species are formed from the existing ones as new changes are introduced into the population via sexual reproduction.
- Examples of sexual reproduction are seen in higher organisms like humans and other mammals, and plants.
Key Differences (Asexual vs Sexual Reproduction)
Basis for Comparison
|Definition||Asexual reproduction is a mode of reproduction that occurs without the fusion of gametes and doesn’t involve the exchange of genetic information, resulting in offsprings identical to their parents.||Sexual reproduction is a mode of reproduction involving a complex life cycle where the formation of new organisms occurs by the combination of genetic information from two different individuals of two different types (sexes).|
|Occurs in||Asexual reproduction mostly occurs in primitive living beings like bacteria, fungi, and primitive plants.||Sexual reproduction is common in higher organisms like multicellular animals, some fungi, and plants.|
|Complexity||Asexual reproduction is less complex than sexual reproduction.||Sexual reproduction is more complex than asexual reproduction.|
|Process||Asexual reproduction is a uni-parental process where a single parent is sufficient to produce a new offspring.||Sexual reproduction is mostly a bi-parental process involving two different parents except in the case of hermaphrodite.|
|Involvement of gametes||Gametes are not involved in asexual reproduction.||Gametes are involved in sexual reproduction.|
|Reproductive units||Somatic cells act as reproductive units during asexual reproduction.||Gametes act as the reproductive units during sexual reproduction.|
|Fertilization||Fertilization doesn’t occur during sexual reproduction.||Sexual reproduction occurs with the fertilization of male and female gametes. Fertilization can be either internal or external.|
|Cell division||Asexual reproduction occurs by a series of mitotic divisions. No meiotic divisions are involved.||Sexual reproduction occurs by a series of mitotic and meiotic divisions.|
|Chromosomes||The chromosomes remain diploid during asexual reproduction.||Meiosis produces haploid chromosomes during sexual reproduction.|
|Types||Depending on the mechanism of the process, asexual reproduction can occur in several ways; fission, budding, vegetative propagation, fragmentation, spore formation, and parthenogenesis.||Sexual reproduction is of several types depending on the mechanism of the process and the parents involved; autogamy, allogamy, syngamy, and conjugation.|
|Diversity||No genetic diversity is brought about by asexual reproduction.||Sexual reproduction is important for introducing genetic diversity within a population.|
|Speed||The process of asexual reproduction is rapid, which is useful for organisms whose strategy to survive is to reproduce rapidly.||The process is also comparatively slower as the production of offsprings in sexual reproduction occurs less rapidly.|
|Organs||Organisms reproducing asexually do not have specialized reproductive organs.||Organisms reproducing sexually have specialized reproductive organs.|
|Offspring||The offspring formed by asexual reproduction are genetically identical.||The offspring formed by sexual reproduction are genetically different.|
|Importance||Asexual reproduction is important as it allows the continuity of genetic information through different generations.||Sexual reproduction is important as it brings genetic variation, which allows the evolution to proceed.|
|Examples||Examples of asexual reproduction are observed in bacteria, most fungi, and some vertebrates like lizards.||Examples of sexual reproduction are seen in higher organisms like humans and other mammals, and plants.|
Video Animation: Asexual and Sexual Reproduction By Amoeba Sisters
Examples of asexual reproduction
- All prokaryotes reproduce by an asexual method where the parent cell doubles its genetic information and then splits to form two identical daughter cells.
- One of the most common processes of asexual division in bacteria is fission, where a single parent cell divides to form two or more identical daughter cells.
- Besides, bacteria reproduction also occurs by other processes involving horizontal gene transfer where genes are transferred from one organism to another instead of vertically from parents to the child.
- This form of reproduction is called asexual as the process doesn’t involve the formation or fusion of gametes.
- Other forms of asexual reproduction like budding, are also observed in other bacterial species.
- Asexual reproduction is essential in bacteria as it allows them to reproduce rapidly, which is their strategy for survival.
- Bacteria are primitive living beings, and they do not have specialized organs or cells for sexual reproduction.
- All bacterial cells are capable of reproducing asexually depending on their stages of development and the environmental conditions.
Parthenogenesis in rock lizards
- Most multicellular animals including invertebrates and vertebrates reproduce mostly by sexual method but some lizards like the rock lizard, geckos, and snakes reproduce by parthenogenesis.
- These asexual species are formed from the hybridization of two or more sexual species forming polyploidy species.
- The exact mechanism of the process is not yet clear, but multiple hybridization events have been seen to occur at the same time.
- Like all other asexual reproduction methods, parthenogenesis also causes a decrease in genetic diversity among individuals.
- Asexual lizards are also mostly found to be females, and the behavior is assumed to be due to the hormonal cycle of the organism. The stimulation for parthenogenesis, however, is believed to be generated via mating behavior stimuli which are remnant of their sexually reproducing past.
- Parthenogenesis is not observed in males because of their genetic incompatibility.
- Some of these lizards are obligatory parthenogenetic while others are facultatively parthenogenetic.
Examples of sexual reproduction
Sexual reproduction in animals
- Most of the higher animals reproduce sexually by the fusion of male and female gametes in the process of fertilization.
- The process of sexual reproduction in animals occurs via a complex cycle consisting of mitotic and meiotic cell divisions.
- In animals, reproductive organs and reproductive cells are well defined. These cells then undergo meiotic divisions to form haploid gametes. The male gametes are termed sperms, whereas the female gametes are termed as eggs.
- The process of fertilization can be either internal or external. Either way, the male gamete fuses with the female gamete to form a diploid zygote. The zygote then develops to form a new organism in due time.
- Reproduction might also be seasonal in some animals like frogs that only reproduce during the rainy season.
- Most animals are unicellular and thus produce one of the two gametes, but some might be hermaphrodites that produce both male and female gametes.
Sexual reproduction in plants
- Sexual reproduction in plants is similar to sexual reproduction in that male and female gametes are involved which later fuse to form a diploid zygote.
- Like in animals, reproductive organs and reproductive cells are well defined in plants as well. The male reproductive organ forms the haploid male gamete termed the pollen grains, and the female reproductive part forms the female gamete termed as ovule or egg.
- The process of fertilization in plants occurs after pollination, during which the male gamete is moved from one plant body to another for reproduction.
- Fertilization in plants can be either self-fertilization or cross-fertilization depending on the number of individuals involved in the process.
- The pollen grains reach the female reproductive organs via pollination, after which it fuses with the female gamete to form a zygote.
- The zygote then develops into a fruit with seeds that are then used to produce new organisms.
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