Search results for "Meiosi"
showing 5 items of 55 documents
Experimental change of cytoplasmic composition can convert determination of blastomeres inPlatynereis dumerilii (Annelida, Polychaeta)
1991
Early development ofPlatynereis dumerilii is characterized by an extremely constant cleavage pattern in which the volumes and cytoplasmic contents of the blastomeres show remarkably little variability (Dorresteijn 1990). In order to test the necessity of a precise partitioning of the cytoplasm, we have stratified the ooplasm by mild centrifugation (10 min at 300 g) after completion of meiosis but before first cleavage. The cytoplasm of the zygote stratifies randomly with respect to the pre-existing animal-vegetal axis, but first cleavage follows the animal-vegetal axis dividing the plasm before it has rearranged to its normal distribution. As usual, first cleavage is unequal in the majority…
Aneiploīdija, dzimumhromosomu izmaiņas un mejotisko gēnu ekspresija vīriešu ļaundabīgajos audzējos: Iespējamā mejotiskā izcelsme
2017
Novērots, ka vairākos vēža tipos DNS sadalījums para-triploīdajā diapazonā (ap 69 hromosomām) ir bieži saistīts ar lielāku ļaundabīgumu, paaugstinātu rezistenci pret ķīmijterapiju un nelabvēlīgu prognozi pacientam. Šobrīd vadošā teorija uzskata, ka triploīdās vēža šūnas veidojas no tetraploīdajām nejaušo anomālo mitožu sērijas rezultātā. Tomēr jaunākie novērojumi liecina, ka triploīdijas rašanās var nebūt pilnīgi nejauša un ka tā varētu būt iesaistīta vēža attīstības svarīgākajās stadijās. Sakarā ar jaunākajiem novērojumiem par to, kādu lomu spēlē vēža cilmes šūnas audzēju pašatjaunošanās procesā, zinātnieki sāka atkārtoti pievērsties 19. gadsimta teorijai, kura uzskata, ka vēža šūnu evolūc…
Protandric hermaphrodite peculiarities in Amphiprion frenatus Brevoort (Teleostei, Pomacentridae)
1990
Electron microscopy of the male phase of the ovotestis of Amphiprion frenatus, a protandric hermaphrodite, showed no connective tissue between male and female areas and, as the basal lamina was lacking both along the seminiferous tubules and round the previtellogenic oocytes, the male and female germ cells were only separated by their respective surrounding somatic cells (Sertoli and follicle cells). Besides previtellogenic oocytes, oocytes in meiotic prophase and very small (young) previtellogenic oocytes, were detected in the ovarian part, as spermatogenesis proceeded, revealing oogenetic activity. Degeneration of some previtellogenic oocytes and their follicle cells was discernible.
Bisphenol A Effects on the Growing Mouse Oocyte Are Influenced by Diet1
2009
Growing evidence suggests that exposure to bisphenol A (BPA) has the ability to disrupt several different stages of oocyte development. To date, most attention has focused on the effects of BPA on the periovulatory oocyte, and considerable variation is evident in the results of these studies. In our own laboratory, variation in the results of BPA studies conducted at different times appeared to correlate with changes in mill dates of animal feed. This observation, coupled with reports by others that dietary estrogens in feed are a confounding variable in studies of endocrine-disrupting chemicals, prompted us to evaluate the effect of diet on the results of BPA studies of the periovulatory o…
Diagnóstico genético ovocitario mediante análisis del primer corpúsculo polar
2023
El desarrollo de nuevas tecnologías de cribado genético informa que la mayoría de la población es portadora, en heterocigosis, de alguna variante patogénica causante de enfermedades monogénicas; generando la mitad de sus gametos libres de la mutación y la otra mitad portadores. En el ámbito de la reproducción humana asistida, el diagnóstico molecular de los ovocitos permitiría seleccionar aquéllos libres de una variante patogénica particular, previamente a la fecundación; maximizando las probabilidades de obtener descendencia sana o portadora, según el escenario particular de cada pareja. Actualmente, el estudio molecular directo del ovocito fecundable no es posible, ya que su diagnóstico i…