Monday, October 18, 2021

What Is Sexual Reproduction In Biology

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Events In Sexual Reproduction

Sexual Reproduction Humans | Genetics | Biology | FuseSchool

As I have mentioned; earlier sexual reproduction is an elaborate processes, it is complete by some events which follow a regular sequence.Sexual reproduction is characterized by formation of male & female gametes, fusion of that gametes followed by formation of zygote and embryo.The most vital step of sexual reproduction is fusion of gametes i.e, Fertilisation.So making a reference to the fertilisation, the whole process is grouped into three distinct stages1. Pre-fertilisation

All the phenomena just before the fusion of gametes include under Pre-fertilisation events.The two main pre-fertilisation events are gametogenesis&gamete transfer.


The term gametogenesis is a combination of two words, gamete&genesis.In biology, genesis term is used to mean formation. So gametogenesis means formation of gamete.



But majority of sexually reproducing organisms produced Heterogametes, morphologically different type of male & female gametes.

Gamete Transfer

As the male & female gametes are produced at different body or different part of body, they should to transfer for fusion.

Motility of Gamete

In a majority of organisms including humans, male gamet is motile while female gamet is non-motile.But there have two exceptional case.In fungi&algae , male & female both type of gametes are motile.In gymnosperm, angiosperm& red algae, male & female both type of gametes are non-motile.

A Benefit Of Heterogamy: Labeling Meiotically Produced Cells To Harness Variation While Enhancing Heterogeneity

Heterogametes in animals and plants generally display morphological differences, i.e., small sperm and large egg cells in comparison with their progenitor meiotic cells. However, as mentioned above, heterogamy in unicellular eukaryotic organisms is frequently determined at the molecular level by a single genetic locus, and can include more than two mating types. If we use the assumption that unicellular eukaryotes evolved prior to multicellular organisms, we may infer that the morphological and/or physiological differentiation of heterogametes in multicellular organisms should be considered elaborations of the very simple differences, such as at a single genetic locus, observed in gametes of unicellular eukaryotes. This inference is consistent with the recent finding that in Volvox, expansion of a mating locus causes heterogametes to change from being equal in size to being dimorphic .

If the essential function of heterogamy is the labeling of meiotically produced cells and thereby harnessing variation while enhancing heterogeneity, there should be a multitude of ways to achieve this. Genetic loci for mating types probably represent the most ancient and simple way, but there could be many other modifications to enhance the differentiation for higher efficiency.

Overview: Gametes Meiosis Fertilization And Mitosis

Sexual reproduction involves the fusion or fertilization of gametes from two different sources or organisms.

Typically, a gamete or reproductive cell is haploid, while the somatic or body cell of the organism is diploid. A diploid cell has a paired set of chromosomes. Haploid means that the cell has a single set of unpaired chromosomes, or one half the number of chromosomes of a somatic cell. In diploid organisms, sexual reproduction involves alternating haploid and diploid phases, with fusion of haploid cells to produce a diploid organism. Some organisms, however, exhibit polyploidy, whereby there are more than two homologous sets of chromosomes.

Meiosis and mitosis are an integral part of cell division. Mitosis occurs in somatic cells. The resultant number of cells in mitosis is twice the number of original cells. The number of chromosomes in the daughter cells is the same as that of the parent cell. Meiosis occurs in reproductive or sex cells and results in gametes. It results in cells with half the number of chromosomes present in the daughter cells as are in the parent cell. Essentially, a diploid cell duplicates itself, then undergoes two divisions , in the process forming four haploid cells. This process occurs in two phases, meiosis I and meiosis II.

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What Is Asexual Reproduction

Asexual reproduction is the process where only one parent is involved giving birth to a progeny. This progeny produced is totally identical to the parent in its genetic makeup. There are organisms that reproduce asexually like bacteria, multicellular organisms like fungi and even plants. Bacteria divides asexually by binary fission. Hydras and yeast reproduce through binary fission. However, these organisms can undergo sexual reproduction.

For example, bacteria can undergo conjugation, hydra and yeast can reproduce sexually. In some invertebrates, parthenogenesis is the process of reproduction. This means, growth of the embryo or seed can take place without fertilization by a male. This is seen in some parasitic wasps, water fleas, aphids, fish and sharks. Asexual reproduction in plants includes many processes like:

  • Budding
  • Regeneration

Diagnosis Of The Genus

#125 Summary of Reproduction

Asexual reproduction: Cell division is by multilateral budding. Pseudohyphae may be absent or poorly developed.

Sexual reproduction: Asci show conjugation between a cell and its bud, or between independent cells. Ascospores are globose, ovoid, or lenticular and have smooth or warty walls that may also have spiral ridges. Ascospores are not liberated from the ascus except in one species, D. udenii. One to two ascospores are usually formed per ascus, but for some species up to four ascospores may be present.

Physiology/biochemistry: Fermentation is positive, weak or absent. Nitrate is not assimilated. The major ubiquinone is CoQ-9. The diazonium blue B reaction is negative.

Phylogenetic placement: Saccharomycetales, Debaryomycetaceae. Debaryomyces and Schwanniomyces are sister genera .

Figure 24.1. Phylogenetic relatedness among species of Debaryomyces and neighboring taxa determined from maximum parsimony analysis of concatenated gene sequences from D1/D2 LSU rRNA and SSU rRNA. Bootstrap values are from 1000 replicates. Strain numbers are followed by GenBank numbers for D1/D2 and SSU gene sequences, respectively. A dash indicates a missing sequence. The D1/D2 sequence for D. subglobosus CBS 792 was provided by M. Groenewald and appears to be identical to that of D. vietnamensis. As discussed in the text, D. mycophilus and D. singareniensis may not be members of the Debaryomyces clade. T=type strain.

José Paulo Sampaio, in, 2011

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Sexual Reproduction Of Protists And Fungi

Asexual reproduction is widespread among fungi and certain protists. However, many fungi and protists also reproduce sexually.

Although protists generally are unicellular, they can exhibit reproductive variances, which may be symbolized by + and – signs , and referred to as “mating strains” or “reproductive types” or similar appellations. At times of reproduction, the “father” cell and the “mother” cell combines together. Next, their genetic information combines together into a new formation, and by cell division the offspring is born.

Fungi may be unicellular or multicellular, and like protists, some unicellular fungi can exhibit reproductive variances. In asexual reproduction, the offspring are genetically identical to the âparentâ organism . Yeasts and other unicellular fungi can reproduce simply by budding, or âpinching offâ a new cell. Many multicellular species produce a variety of different asexual spores that are easily dispersed and resistant to harsh environmental conditions. When the conditions are right, these spores will germinate and colonize new habitats. During sexual reproduction in fungi, a mixing of genetic material occurs so that the offspring exhibit traits of both parents.

Advantages Of Asexual Reproduction

  • One parent is needed to complete the process of asexual reproduction.
  • In majority of the cases, one is sure an offspring will be produced.
  • The gestation period or growth period is very short.
  • The offspring has the same phenotype and genetic make up as the parent.
  • As there is no cross over or recombination of genes involved, chance of mutation is very less.

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Asexual Vs Sexual Reproduction

There are many organisms that reproduce either asexually or sexually. The following article will discuss some points that will help you understand the differences between these two reproductive strategies. Read on to know more about the potential benefits of these strategies for different organisms.

There are many organisms that reproduce either asexually or sexually. The following article will discuss some points that will help you understand the differences between these two reproductive strategies. Read on to know more about the potential benefits of these strategies for different organisms.

The biological process that helps give rise or birth to new organisms from their parents is called reproduction. Each and every organism on the world survives because they have the ability to reproduce and propagate their own kind. There are two broad categories of reproduction. These include asexual reproduction and sexual reproduction. These two methods are used by plants and animals to ensure their species continues to survive. Let us have a look at asexual vs. sexual reproduction and learn the differences between the two.

Sexual Version Asexual Reproduction

Sexual Reproduction in Plants | Plants | Biology | FuseSchool
Main article:Reproduction#Asexual vs. sexual reproduction

Sexual reproduction is a near-universal mode of reproduction among eukaryotes. Even some groups of organisms that practice asexual reproductionâsuch as fungi, certain protists and vascular plants, various invertebrates, and even some reptiles and amphibiansâexhibit sexual reproduction as well. Lahr et al. contend that even in amoeboid lineages the extent of asexual reproduction in overestimated and that the evidence “demonstrates that the majority of amoeboid lineages are, contrary to popular belief, anciently sexual, and that most asexual groups have probably arisen recently and independently.” Among animals, nearly all species practice sexual reproduction. Mayr notes that “above the level of the genus there are only three higher taxa of animals that consist exclusively of uniparentally reproducing clones.”

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Premises For Proposal Of The Src

We begin with the basic facts based on which the SRC was hypothesized.

Firstly, although DNA transmission in prokaryotes is sometimes referred to as recombination , it is widely accepted that sex and sex differentiation are phenomena occurring in eukaryotes, which contain chromosomes, nuclei, cell skeletons, and the mitotic cell cycle, regardless of the obscurity of their evolutionary origins . We would restrict our discussion in eukaryotes.

Secondly, meiosis is highly conserved in almost all known eukaryotes, including animals, plants, fungi, and protists . It is also widely accepted that meiosis may originate from mitosis, probably via occasional mistakes in cohesin binding and/or digestion on chromosomes .

Thirdly, despite the extreme diversity of morphology and recognition mechanisms of gametes, cell fusion of two haploid gametes into a new diploid zygote is conserved in all eukaryotes.

Fifthly, regardless of the presence or absence of germlines, e.g., in animals or plants, respectively, , new generations in all multicellular organisms are generated through sexual reproduction consisting of the three key events: meiosis, sex differentiation, and fertilization. With this view, sexual reproduction is predicted to be more ancient than multicellular structures as sexual reproduction already existed in unicellular eukaryotic organisms.

Examples Of Asexual Reproduction

Asexual reproduction in plants

ChlorophytumBryophyllum propagatedDo not confuse asexual reproduction with reproduction in flowering plants, which often combine both male and female parts in the same flower. Fruitsseedssexual reproductionvegetative growthvegetablesEach of the examples of food plants below uses asexual and sexual reproduction in different ways

More about bacteria

Asexual reproduction in animals


Hydra with 2 budsAphid giving birthIdentical twins are produced by a form of asexual reproduction when the ball of cells making up the embryo breaks into two, and each implants in the uterus and grows independently

See weblink below.

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Sequential Differentiation Or Integration Of Independently Evolved Events

In animals, meiosis and gametogenesis occur sequentially in germlines and sex differentiation occurs in somatic gonads into which the germline migrated. In plants, meiosis and gametogenesis occur separately from somatic cells of the sporophyte and gametophyte, while sex differentiation could occur either in sporophyte or gametophyte. How were meiosis, gametogenesis, and sex differentiation originally integrated? Considering that all three processes exist in protists, one possible scenario is that each evolved independently, and they were integrated together as a coordinated process by chance and thereafter genetically fixed as a program in protists. This scenario is possible because all three processes, meiosis, heterogametogenesis , and fertilization, occur at the cellular level. Protists are unicellular eukaryotes and live in a population. These two characteristics provide the required conditions for SRC emergence: on one hand each cell can behave independently for emergence of meiosis and gametogenesis, and on the other, all cells live together closely enough to make both cell fusion and cellcell recognition possible. Integration of the three events would have brought all of their selective advantages together and such integration, now referred as SRC, would be therefore selected during evolution.

The Red Queen Hypothesis

Sexual reproduction pros and cons

It is not in dispute that sexual reproduction provides evolutionary advantages to organisms that employ this mechanism to produce offspring. But why, even in the face of fairly stable conditions, does sexual reproduction persist when it is more difficult and costly for individual organisms? Variation is the outcome of sexual reproduction, but why are ongoing variations necessary? Possible answers to these questions are explained in the Red Queen hypothesis, first proposed by Leigh Van Valen in 1973.

All species co-evolve with other organisms; for example, predators evolve with their prey and parasites evolve with their hosts. Each tiny advantage gained by favorable variation gives a species an edge over close competitors, predators, parasites, or even prey. The only method that will allow a co-evolving species to maintain its own share of the resources is to also continually improve its fitness. As one species gains an advantage, this increases selection on the other species; they must also develop an advantage or they will be out-competed. No single species progresses too far ahead because genetic variation among the progeny of sexual reproduction provides all species with a mechanism to improve rapidly. Species that cannot keep up become extinct. The Red Queenâs catchphrase was, âIt takes all the running you can do to stay in the same place.â This is an apt description of co-evolution between competing species.

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Disadvantages Of Asexual Reproduction

  • As the genetic material from parent is directly passed on to the off spring, it causes all the diseases and defects to be passed on to the offspring as well.
  • As no recombination of genes occurs, chances of evolution are very low.

As you can see both these methods have plenty of differences, but both lead to reproduction of progeny. According to the various species, these methods prove to be a successful way to sustain life.

The Concept Of The Sexual Reproduction Cycle And Its Evolutionary Significance

  • State Key Laboratory of Protein & Plant Gene Research, Quantitative Biology Center, College of Life Science, Peking University, Beijing, China

The concept of a sexual reproduction cycle was first proposed by Bai and Xu to describe the integration of meiosis, sex differentiation, and fertilization. This review discusses the evolutionary and scientific implications of considering these three events as part of a single process. Viewed in this way, the SRC is revealed to be a mechanism for efficiently increasing genetic variation, facilitating adaptation to environmental challenges. It also becomes clear that, in terms of cell proliferation, it is appropriate to contrast mitosis with the entire SRC, rather than with meiosis alone. Evolutionarily, it appears that the SRC was first established in unicellular eukaryotes and that all multicellular organisms evolved within that framework. This concept provides a new perspective into how sexual reproduction evolved, how generations should be defined, and how developmental processes of various multicellular organisms should properly be compared.

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Sexual Reproduction And Diversity: Connection Between Sexual Selection And Biological Communities Via Population Dynamics

Hokkaido Forest Research Station, Field Science Education and Research Center, Kyoto University, Hokkaido, Japan


Kazuya Kobayashi, Hokkaido Forest Research Station, Field Science Education and Research Center, Kyoto University, 553 Tawa, Shibecha-cho, Kawakami-gun, Hokkaido 088-2339, Japan.

Hokkaido Forest Research Station, Field Science Education and Research Center, Kyoto University, Hokkaido, Japan


Kazuya Kobayashi, Hokkaido Forest Research Station, Field Science Education and Research Center, Kyoto University, 553 Tawa, Shibecha-cho, Kawakami-gun, Hokkaido 088-2339, Japan.

Funding information: JSPS KAKENHI, Grant/Award Number: 17H05048

Reproduction: Asexual Vs Sexual

GCSE Biology – Sexual vs Asexual Reproduction – What is Asexual Reproduction? #46

Cell division is how organisms grow and repair themselves. It is also how many organisms produce offspring. For many single-celled organisms, reproduction is a similar process. The parent cell simply divides to form two daughter cells that are identical to the parent. In many other organisms, two parents are involved, and the offspring are not identical to the parents. In fact, each offspring is unique. Look at the family in Figurebelow. The children resemble their parents, but they are not identical to them. Instead, each has a unique combination of characteristics inherited from both parents.

Family Portrait: Mother, Daughter, Father, and Son. Children resemble their parents, but they are never identical to them. Do you know why this is the case?

Reproduction is the process by which organisms give rise to offspring. It is one of the defining characteristics of living things. There are two basic types of reproduction: asexual reproduction and sexual reproduction.

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Importance Of Genetic Variation

George Williams compared reproduction to a raffle in which one can either have many tickets with different numbers or many tickets with the same number . If one doesn’t know which number will be drawn in a raffle, it is better to have many different tickets. Similarly, organisms producing many unique individuals in an unpredictable environment have a greater chance that at least some their offspring will survive. Thus, Williams proposed that sexual reproduction evolved because of the benefits gained by organisms in fluctuating physical environments. This is often called the”bet-hedging” or “tangled bank” hypothesis.

Others argue that sexual reproduction evolved because of advantages gained in the face of changes in other organisms. Predators, prey, and parasites constantly improve their efficiency at capturing prey, evading predators, and extracting nutrients from hosts. Genetically variable offspring offer more opportunities for each to increase its efficiency. This is called the”Red Queen” hypothesis after the popular book, Alice in Wonderland, in which the queen tells Alice, “Now here, you see, it takes all the running you can do, to keep in the same place.”

Michelle J. Solensky

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