Cell Cycle and Chromosomes

 Both Assertion and Reasoning are true and R is the correct explanation of A. If karyokinesis is not followed by cytokinesis the cell becomes multinucleate or coenocytic or syncytial. Striated muscle fibers show striations with many nuclei in their striations. It shows syncytial condition.

If a chromosome segment gets inserted in interstitial position of a non-homologous chromosome, it is known as shift translocation. In humans, it is invariably associated with myelogenous leukemia.

This type of mutation takes place between two chromosomes and interchanges their chromosome segments. In other words, a portion of chromosome is transferred on to other chromosome.

ZNF259 where the gene ZNF259 plays an important role as a signaling molecule. ZNF259 communicates mitogenic signals from the cytoplasm to the nucleus and interacts with tyrosine kinase receptors.

This state results from an abnormal swap over of genetic material between chromosomes. This swap over occurs as a chance event in the father of an affected person during the formation of sperm cells. The translocation affects the gene in charge that is SRY for development of a fetus into a male. 

The longest phase in prophase I of meiosis is  pachytene.

The number of cells formed from one cell at the end of Meiosis II are 4.

The transition stage of meiotic prophase I to metaphase I is diakinesis.

The cell cycle consists of a mitotic (M) phase, during which first nuclear division (mitosis) and then cell division (cytokinesis) take place. The shortest phase in the cell cycle is M phase

The cell cycle consists of a mitotic(M) phase, during which first nuclear division (mitosis) and then celldivision (cytokinesis) take place. The M phase is followed by a long period of growth known as interphase. Interphase has three subphases (G1, S and G2) in cells that divide.

In cell cycle process, the term generation time is used to refer the time required for the completion of cell cycle.

The type of cell division occuring during the maturation phase of spermatogenesis is meiosis in which half the chromosomes of the parent cells are formed.

The homologous chromosomes pair by adhering along their lengths, a process called synapsis. This process occurs in zygotene.

The most active phase of nucleus during cell division is interphase, in which all the metabolic activities like chromosome and centriole duplication, DNA replication, cell growth etc. take place. 

The place where mitotic spindle attaches to chromosomes is called kinetochore.