Tham khảo tài liệu 'a dictionary of genetics phần 7', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 344 polar body polar body the minute cell produced and discarded during the development of an oocyte. A polar body contains one of the nuclei derived from the first or second division of meiosis but has practically no cytoplasm. See ootid nucleus. polar fusion nucleus in plants the product of the fusion of the two polar nuclei. This after fusing with a male nucleus gives rise to the tripoid endosperm nucleus. See double fertilization. polar gene conversion a phenomenon in which a gradient of conversion frequencies exists from one end of a gene to the other sites closer to one end of a gene usually have higher conversion frequencies than do those farther from that end. polar granules electron-dense membrane-less RNA-protein complexes often associated with mitochondria found in the pole plasm . and subsequently incorporated into primordial germ cells . in a variety of species. Also called germinal granules or P granules. polarity gradient the quantitative effect of a polarity mutation in one gene on the expression of later genes in the operon. The effect is a function of the distance between the nonsense codon and the next chain-initiation signal. polarity mutant 1. a mutant gene that is able to reduce the rate of synthesis of the proteins that normally would be produced by wild-type alleles of the genes lying beyond it on the chromosome. Such genes exert their effect during the translation of a polycistronic message . . See regulator gene translation. 2. a mutant gene that influences polarized patterns of embryonic development. See bicoid engrailed hunchback maternal polarity mutants zygotic segmentation mutants. polarization microscope a compound light microscope used for studying the anisotropic properties of objects and for rendering objects visible because of their optical anisotropy. polar nuclei See ootid nucleus pollen grain polo-cyte. polaron a chromosomal segment within which polarized genetic recombination takes place by gene conversion. polar .
