1 2 Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction.
Asexual reproduction is the primary form of reproduction for single-celled organisms such as the archaea, bacteria, and protists.
Sexual reproduction is the production of new living organisms by combining genetic information from two individuals of different types (sexes). In most higher organisms, one sex (male) produces a small motile gamete which travels to fuse with a larger stationary gamete produced by the other (female).
3 4 5 6 Sexual reproduction is a form of reproduction which involves the fusion of male and female reproductive cells (gametes) to create azygote in a process called fertilization. The gametes may come from different individuals or the same individual (self- fertilization), and are created by meiosis, a specialized type of cell division. Gametes have half the number of chromosomes found in other cells from the same organism.
During fertilization the chromosomes from the gametes are combined, restoring the usual number of chromosomes in the zygote. Thus, the zygote includes genetic material from both gametes. Sexual reproduction is the primary method of reproduction for the vast majority of macroscopic organisms, including almost all eukaryotes (which includes animals and plants).
7 In the first stage of sexual reproduction, "meiosis", the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). During "fertilization", haploid gametes come together to form a diploid zygote and the original number of chromosomes is restored.
8 Sexual dimorphism is a phenotypic differentiation between males and females of the same species. This differentiation happens in creatures who reproduce through sexual reproduction, with the prototypical example being for differences in characteristics of reproductive organs. Other possible examples are for secondary sex characteristics, body size, physical strength and morphology, ornamentation, behavior and other bodily traits. Traits such as ornamentation and breeding behavior found in one sex only imply sexual selection. Sexual selection over an extended period of time leads to sexual dimorphism.[1]
9 10 In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both partners can act as the "female" or "male".
For example, the great majority of tunicates, pulmonate snails, opisthobranch snails and slugs are hermaphrodites. Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates. Most plants are also hermaphrodites.
11 12 13 14 15 16 An amoeba reproduces asexually by a process called binary fission.
» It starts by pulling in the pseudopodia to attain a spherical shape.
» Mitotic cell division takes place, which constricts the nucleus and cytoplasm to form two daughter cells.
» Thus, the genetic information in the nucleus is copied in both the cells which makes them identical. The nucleus is the most vital part of an amoeba and is the key to its survival. The free amoebae are called trophozoites. Binary fission in amoebae may last for anywhere around 30 - 60 minutes under ideal conditions.
Amoeba can also reproduce by a process called multiple fission. It usually applies this process under abnormal circumstances, wherein the environment lacks the necessary nutrients. The process begins in the same way as binary fission.
» Amoeba retracts its pseudopodia and attains a more spherical shape.
» In hostile or dangerous situations, where natural conditions make survival difficult for the amoeba, it forms a protective covering, like a wall around itself to form a cyst. This cyst is able to survive harsh and rough conditions which are potentially harmful for a normal amoeba.
» Inside the cyst, multiple mitosis takes place. This process produces many daughter cells inside the cyst, which are protected against the unsuitable environment.
» Once favorable conditions prevail, the cyst ruptures and daughter amoebae are released from it. These cysts are responsible for causing infection and contaminating food and water.
The amoeba that is armored in protective covering around itself is often termed as 'microbial cyst.' If the amoeba stays in the microbial cyst stage for a long time, it may die due to lack of food and will also be incapable of reproducing.
17 Budding is a form of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. The new organism remains attached as it grows, separating from the parent organism only when it is mature, leaving behind scar tissue.
18 Fragmentation or clonal fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning in which an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism.
19 20 21 22 Deoxyribonucleic acid (i/diˌɒksiˌraɪbɵ.njuːˌkleɪ.ɨk ˈæsɪd/; DNA) is a molecule that carries most of the genetic instructions used in the development and functioning of all known living organisms and many viruses. Ribonucleic acid (RNA) is a polymeric molecule implicated in various biological roles in coding, decoding, regulation, and expression of genes.
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