Crossword clues for parthenogenesis
Longman Dictionary of Contemporary English
The Collaborative International Dictionary
parthenogenesis \par`the*no*gen"e*sis\ (p[aum]r`th[-e]*n[-o]*j[e^]n"[-e]*s[i^]s), n. [Gr. parqe`nos a virgin + E. genesis.]
(Biol.) The production of new individuals from virgin females by means of ova which have the power of developing without the intervention of the male element; the production, without fertilization, of cells capable of germination. It is one of the phenomena of alternate generation. Cf. Heterogamy, and Metagenesis.
(Bot.) The production of seed without fertilization, believed to occur through the nonsexual formation of an embryo extraneous to the embryonic vesicle.
Douglas Harper's Etymology Dictionary
"reproduction without fertilization," 1849, from Greek parthenos "virgin," of unknown origin, + -genesis "birth, origin, creation." Related: Parthenogenetic.
n. 1 (context biology English) (non-gloss definition: Referring to various aspects of asexual reproduction:) 2 # (context biology uncountable English) reproduction by the development of a single gamete (''viz.'' an ovum or ovule) without fertilisation by a gamete of the opposite sex; compare (term metagenesis English), (term heterogamy English). 3 # (context biology uncountable formerly English) asexual reproduction ''in toto''; agamogenesis. 4 # (context biology countable rare English) An instance or example of parthenogenesis. 5 (context countable and uncountable English) ''figurative uses of the biologic senses'' 6 (context theology English) virgin birth, in reference to the Virgin Mary and Jesus Christ.
Parthenogenesis (; 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 and is a component process of apomixis.
Gynogenesis and pseudogamy are closely related phenomena in which a sperm or pollen triggers the development of the egg cell into an embryo but makes no genetic contribution to the embryo. The rest of the cytology and genetics of these phenomena are mostly identical to that of parthenogenesis.
The term is sometimes used inaccurately to describe reproduction modes in hermaphroditic species that can reproduce by themselves because they contain reproductive organs of both sexes in a single individual's body. However, these species still use fertilization.
Parthenogenesis occurs naturally in many plants, some invertebrate animal species (including nematodes, water fleas, some scorpions, aphids, 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.
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).
Usage examples of "parthenogenesis".
In either case, then, whether with hybrids or in cases of parthenogenesis, the early death of the embryo is due to inability to recollect, owing to a fault in the chain of associated ideas.
If by some miracle she and Annie had been able to decipher the ancient secrets of parthenogenesis, their child would have looked a lot like Rainey, she realized as she flipped through the sketches, turning them this way and that.
Millennia-old problems in the artificial production of cellular life were solved with sober single-mindedness, and parthenogenesis allowed literally billions of females of all species to have the offspring that a cruel Nature forbade them to bear.
Some workers, indeed, are capable of parthenogenesis, and give birth to children who never had fathers.
This last class, besides seeking to balance the sex ratio, perhaps had in mind the fact or rumor that human parthenogenesis had been achieved.
Utopia of sorts, created and inhabited by people who are neither men nor women but something else, who reproduce by grafted uterus and surgery, a kind of artificial parthenogenesis, if you like.
There the Coven surely would have perished, since all had sworn not to reproduce until parthenogenesis was a reality.
That was the rationale behind early parthenogenesis experiments on Herlandiaattempting to cull masculinity from the human process entirely.
At a pinch, and by dint of seeing seventy times books and kids bracketed together, one would think that they are equally the fruits of imagination and dream, the miraculous products of an ideal parthenogenesis able to give at once to woman, apparently, the Balzacian joys of creation and the tender joys of motherhood.
Since I intentionally desexed them entirely, even to parthenogenesis, I found this a bit thick.
I can only conclude that our egg cells are formed through mitosis rather than the usual meio sis, which would more or less halve the number of chromosomes yet again: how else to explain generation upon generation of parthenogenesis?