Page 70 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Cell / 55

own genetic material, they also insert the be replicas of the original cells. Mitosis, the
division of somatic cells to produce two
recombinant DNA.
VetBooks.ir uals produced by asexual means. Cloning daughter cells, includes the duplication of
Clones are genetically identical individ­
genetic material for each daughter cell.
has been accomplished by splitting an Even though the process of cell division is
early‐stage multicell embryo into single normally a continuous process, here it has
cells, which continue their development been divided into periods, or phases, for
into identical individuals. This technique ease of communication about the process.
has been successfully used in domestic The active phases are primarily based on
animals. Clones have also been produced nuclear changes visible by light microscopy.
by nuclear transfer. In this technique, They are prophase, prometaphase, meta­
nuclei obtained from cells of adult animals phase, anaphase, and telophase (Fig. 2‐25).
are transferred into oocytes with their
original nucleus removed. The oocytes Interphase. The period between active
with the transferred nucleus can be placed cell divisions is the interphase. This period
in the uterus of an appropriate female for may vary from a matter of hours in actively
gestation. proliferating tissue to an almost permanent
condition in cells that no longer divide,
such as mature cardiac muscle cells. The
Cell Division replication of DNA during interphase
prepares the cell to begin mitosis. Two
Mitosis pairs of centrioles are also replicated
during interphase and will begin to move
Each day millions of cells in the body of any apart from each other as a complex of
normal animal die, are degraded, or are microtubules begins to form. Microtubules
sloughed from epithelial surfaces. These growing radially away from each of the
cells must be replaced if normal life is to centrioles are called the aster and are
continue, and the replacement cells must found in each end of the cell.

(A) (B) (C)

(D) (E) (F)

Figure 2-25. Overview of the phases of mitosis. (A) Interphase. (B) Prophase. (C) ProMetaphase. (D)
Metaphase. (E) Anaphase. (F) Cytokinesis with DNA (blue) and microtubules (green) visible in PtK1 (rat
kangaroo) cells. Source: micrographs courtesy of Keith DeLuca, Colorado State University, Fort Collins,
Colorado, USA.