Question

What is parthenogenesis with suitable examples

Answer 1

parthenogenesis is a type of asexual reproduction in which the offspring develops from unfertilized eggs. It is particularly common amongst arthropods and rotifers, can also be found in some species of fish, amphibians, birds, and reptiles, but not in mammals. Parthenogenetic development also occurs in some plants species, such as roses and orange trees.

Most animal species that reproduce parthenogenetically also display a phase of sexual behaviour and sexual reproduction. In most cases, parthenogenetic reproduction occurs when environmental conditions are favourable and there is plenty of food that can sustain the generation of large numbers of individuals in a short period of time.

When external conditions change and food supplies become less abundant, or when the environment becomes unpredictable, these species shift to a sexual mode of reproduction. Although sexual reproduction is considerably slower and generates fewer organisms, it gives rise to individuals containing variations in their genetic material. Some of these individuals might be at an advantage over their predecessors, because they might be more able to adapt to new conditions.

In some species of insects, such as the aphids, parthenogenetic reproduction occurs in the spring and summer, when conditions are favourable for rapid population growth. As time goes by and conditions become less favourable, the parthenogenetically born individuals mate and lay fertilized eggs. These eggs hatch the following spring, when conditions are again favourable for another cycle of parthenogenetic reproduction.

In some species of ants, bees, and wasps, the ability to reproduce both sexually and asexually is part of the mechanism establishing sexual differences.

Usually, females develop from unfertilized eggs, containing only half of the genetic material of the mother, whereas males develop from fertilized eggs, containing the genetic contributions of both mother and father.

In other species of insects, such as the rotifers, females produce unfertilized eggs that develop into females during the spring and summer. This process goes on for several generations. During the autumn, smaller eggs are laid, which develop into individuals lacking a digestive system, but capable of secreting sperm. These individuals mate with females, who then produce highly resistant, fertilized eggs that remain viable during long periods of unfavourable conditions. These eggs hatch in the following spring, giving rise only to females, who then engage in a new period of parthenogenetic reproduction.

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Answer 2

Parthenogenesis (/ˌpɑːrθɪnoʊˈdʒɛnɪsɪs, -θɪnə-/;from the Greek παρθένος, parthenos, 'virgin' + γένεσις, genesis, 'creation'[]) is a natural form of asexual reproduction in which growth and development of embryos occur without fertilization. In animals, parthenogenesis means development of an embryo from an unfertilized egg cell. In plantsparthenogenesis is a component process of apomixis.

Parthenogenesis occurs naturally in some plants, some invertebrate animal species (including nematodes, water fleas, some scorpions, aphids, some mites, some bees, some Phasmida and parasitic wasps) and a few vertebrates (such as some fish,[amphibians, reptiles[] and very rarely birds This type of reproduction has been induced artificially in a few species including fish and amphibians.[

Normal egg cells form after meiosis and are haploid, with half as many chromosomes as their mother's body cells. Haploid individuals, however, are usually non-viable, and parthenogenetic offspring usually have the diploid chromosome number. Depending on the mechanism involved in restoring the diploid number of chromosomes, parthenogenetic offspring may have anywhere between all and half of the mother's alleles. The offspring having all of the mother's genetic material are called full clones and those having only half are called half clones. Full clones are usually formed without meiosis. If meiosis occurs, the offspring will get only a fraction of the mother's alleles since crossing over of DNA takes place during meiosis, creating variation.

Parthenogenetic offspring in species that use either the XY or the X0 sex-determination system have two X chromosomes and are female. In species that use the ZW sex-determination system, they have either two Z chromosomes (male) or two W chromosomes (mostly non-viable but rarely a female), or they could have one Z and one W chromosome (female).