DGS 3223 Chapter Notes - Chapter 2: Blastula, Cytogenetics, Centromere
8 Sep 2016
School
Department
Course
Professor
Document Summary
Distinguishing features of meiosis: reduction in chromosome number. Nucleus undergoes one reduction but there are 2 divisions. Chromosomes replicate once, nucleus divides twice: pairing of homologous chromosomes, crossing over occurs. Exchange of like/homologous segments of chromatids: phases of meiosis i. Chromosomes begin to condense, but not yet visible by light microscope. Chromomeres (chromosomes in the process of condensing; darker staining) become visible. Dna synthesis takes place in human oogenesis; in some organisms dna synthesis is pre-meiotic. Acrocentrics have only initiation point (near the synapsis); all other chromosomes have 2. Synaptonemal complex (where they initiate) is seen with electron microscope. Avery welch medical cytogenetics prelim 1 chapter 2 the cell & cell cycle. The paired homologs form bivalents (also called tetrads) Crossing over occurs, resulting in exchange of homologous segments of non-sister chromatids. Homologs begin to repel each other until they are held together only at points where crossing-over took place (chiasmata)
