BIO SCI 97 Chapter Notes -Gamete, Mendelian Inheritance, Synaptonemal Complex
30 Jan 2014
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Document Summary
Paired homologs are called tetrads, due to the four visible chromatids. Recombination nodules can be seen at intervals in the synaptonemal complex. These are aggregates of enzymes and proteins needed for crossing over between homologs. Chromosomes continue to condense in diplotene, and the synaptonemal complex begins to dissolve. Homologs pull apart slightly, revealing chiasma, at locations where crossing over has occurred. Cohesin protein is present between sister chromatids, to resist the pulling forces of kinetochore microtubules. Kinetochore microtubules move synapsed chromosome pairs toward the metaphase plate. Homologous chromosomes align and the synaptonemal complex (protein bridge) is formed between them. This tri-layer protein structure tightly binds nonsister chromatids of homologous chromosomes. Nonsister chromatids belong to different members of a homologous pair. Separation of homologs and sister chromatid in meiosis constitutes the mechanical basis of mendel s laws. For example, in an organism that is genotype aa, the homologs bearing a and a separate from one another during anaphase i.
