The stem region of a plant where one or more leaves attach. Where leaves are attached to stems. The failure of chromosomes to separate properly during cell division. The unequal segregation of chromosomes during meiosis . Thought to be a common cause for Down Syndrome, where sufferers often have an extra copy of chromosome 21.
Common examples are the mosses and liverworts.
In chordates, a cellular rod that runs the length of the body and provides dorsal support. Also, a structure of mesoderm in the embryo that will become the vertebrae of the spinal column. The stiff rod-like structure that all members of the Phylum Chordata develop at some stage during their life. In prokaryotic cells, a region containing the cell's genetic information. Unlike the nucleus in eukaryotic cells, it is not surrounded by a membrane.