some Important Points of Cell Cycle

Cell cycle of Class 11

Dinomitosis It is a type of nuclear division in dinoflagellates in which (i) nuclear membrane does not disappear (ii) microtubular spindle is not formed (iii) chromosomes move while attached to inner nuclear membrane.

Endomitosis It is the multiplication of chromosomes present in a set in nucleus without karyokinesis and cytokinesis.

c-mitosis It is colchicine induced mitosis

Intranuclear division. Mitosis is extra cellular division as spindle is formed outside the nucleus, in cytoplasm. In fungi spindle is formed inside nucleus (intranuclear spindle) from spindle pole bodies (SPBS).

Nuclear membrane remains intact. Nucleus divides by furrow. This type of division is called karyochorisis.

Non disjunction (Bridges 1916) is the failure of particular pair/s of homologous chromosomes or sister chromatids of a chromosome to separate and move at anaphase I so that one daughter cell gets one or few chromosomes more than the other cell.

Free nuclear cell division The nucleus divides repeatedly without cytokinesis to make cell multinucleated (coenocytic/syncytial) e.g., Vaucheria, muscle cell, Opalina.

He La cells These are aneuploid human epithelial cells taken, from Miss Henrietta Lacks in 1951 suffering from cervix cancer.

Synaptinemal complex It is a ribonucleoprotein complex developed between two synapsed homologous chromosomes in zygotene stage. It persists upto pachytene and begins to disappear in diplotene stage except at chiasmata. It has a central element of ribonucleoprotein between two homologous chromosomes and two lateral elements between sister chromatids of each chromosome. The central element contains mainly RNA and protein but the lateral elements are rich in DNA, RNA and protein.

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