. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 10 min. mm Figure 1. Diagrams of the unfertilized egg and fertilized eggs through 16 min after insemination. The distribution of yolk and the sperm aster are not shown. The unfertilized egg has the first polar body and is in second meiotic metaphase. The egg cortex contains numerous cortical granules, and in the vegetal third of the egg there are sheets of dense granules interleaved with endoplasmic reticulum just beneath the layer of cortical granules. At 45 s. most of the cortical granules have undergone exocytosis, the sp
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 10 min. mm Figure 1. Diagrams of the unfertilized egg and fertilized eggs through 16 min after insemination. The distribution of yolk and the sperm aster are not shown. The unfertilized egg has the first polar body and is in second meiotic metaphase. The egg cortex contains numerous cortical granules, and in the vegetal third of the egg there are sheets of dense granules interleaved with endoplasmic reticulum just beneath the layer of cortical granules. At 45 s. most of the cortical granules have undergone exocytosis, the sperm has entered, the axoneme has largely dispersed, and the sheets of dense granules and endoplasmic reticulum have formed into whorls to constitute the vegetal pole plasm. By 2 min. the egg is in second meiotic anaphase. the cortical reaction is complete, and the sperm nucleus has migrated to the vegetal cytoplasm and formed a small aster, with which a small cluster of mitochondria is associated. By 6 min, the egg is in telophase of the second meiotic division, the sperm nucleus has swollen, and the peripheral chromatin has condensed more than the central chromatin. A cloud of mitochondria surrounds the sperm nucleus. By 10 min, the second polar body has formed. The nuclear envelopes have formed around individual or groups of maternal chromosomes. These chromosome-containing vesicles are fusing to form the maternal pronucleus. The enlarged male pronucleus is surrounded by a larger cloud of mitochondria and has migrated partway towards the female pronucleus. By 16 min. the second polar body has separated from the egg. and the pronuclei have met and are associated with an asymmetric cloud of mitochondria brought by the male pronucleus. eggs ofBranchiostomafloridaem the animal hemisphere, although the sample size is far too small to rule out the possibility that sperm can also enter in the vegetal hemi- sphere. By 45 s after insemination, the cortical reaction is nearly complete,
Size: 1471px × 1698px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
