Into the mitosis anaphase initiate by the office of the centromeres, in meiosis this doesn’t are present before anaphase from the following section (maybe not shown)
The new Family from Mitosis and Meiosis (centered on Darlington). Keep in mind that the chromosomes try double on the very first looks for the mitosis, however from the very first (leptotene) phase off meiotic prophase. They couples during the zygotene, start to getting double (split) during the pachytene, and are usually twice in the last degree out-of meiotic prophase (diplotene and you may diakinesis). The newest Aspects Of your CHROMOSOMES II5 facts meant for telosynapsis was adduced on occurrence off continuing bands away from chromosomes at the meiotic metaphase in some organisms (chiefly Oenothera), but some other so much more satisfactory explana- tion can get for it (p. Darlington are the first to suggest that whether your parasynaptic interpre- tation is actually followed, most of the differences between meiosis and you will mitosis normally, with the help of very few hypotheses, feel deduced from the brand new difference between the fresh new singleness otherwise doubleness of prophase posts.
The guy suggested you to homologous chromosomes, or in other words homologous chromonemata, notice each other during the pairs. It appeal was met from inside the mitotic prophase, yet not during the early meiotic prophase, where chromosomes is at basic unmarried, and can only match the interest because of the upcoming together inside the zygotene pairing. Into the meiosis, the brand new spHtting of the chromosomes, which takes place in the fresh new interphase before a great mitotic department, cannot takes place right up until pachytene if chromosomes already are relevant within the sets. It therefore supplies a collection of four relevant posts and these break apart to the diplotene loops, are held along with her from the changes out-of spouse at chiasmata.
Hence Darlington supposed your spUtting away from a chromosome in preparation for another mitotic section happens in the interphase before that section, and that the fresh new singleness of one’s meiotic chromo- somes is due only to that it initiate condensation and you will swindle- grip to your section before the busting have occurred. That it hypo- thesis is called the fresh Precocity Idea. A modification of the simple precocity theory has been proposed because of the Huskins,^ just who accepts Darhngton’s hypotheses that differences when considering the 2 types off division are due to the fresh repulsion between pairs out of chromonemata and you can appeal ranging from solitary chromonemata, but denies Darlington’s membership of the provider of singleness regarding new meiotic chromosomes inside prophase. Centered on Huskins, this new busting of your chromosomes for one section happen through the the earlier office, developing a therefore-named tertiary separated that creates the chromo- certain pairs on mitotic metaphase to get in reality quadripartite, those in the meiotic metaphase octopartite bodies.
The latest falling aside of your own four posts try research that even in the event one or two homologous chromosomes notice one another, you to definitely set of homologous chromonemata repels another similar partners
Within the interphase just before meiosis, that it tertiary spUt must be allowed to be shed in a few ways, only to getting restored on pachytene; within the fresh diakinesis phase it ^ Cf. Huskins and you may Smith 1934. Il6 An introduction to Progressive Genes try succeeded from the various other split up to your department and therefore pursue the second meiotic office. The 2 theories render a bit different membership out of anaphase separa- tion. Considering Darlington, the first breakup of one’s chromo- somes from inside the anaphase is during mitosis as a result of the office from the fresh new centromeres during this period plus in meiosis in order to a heightened repulsion amongst the centromeres and this now starts to beat the fresh new pushes holding the chromosomes along with her in the chiasmata. Predicated on Huskins, on top of that, the newest break up of your mitotic chromosomes is analogous into creation of diplotene loops ; it’s due to the synthesis of the fresh tertiary split up and therefore converts the fresh new matched mitotic chromosomes into a pair of mutually repelling matched posts.
