The most drastic upset in chromosome number is an entire extra set, a condition called polyploidy. This results from formation of a diploid (rather than a normal hap-loid) gamete. For example, if a haploid sperm fertilizes a diploid egg, the fertilized egg is triploid, with three copies of each chromosome. Most human polyploids die as embryos or fetuses, but occasionally an infant survives for a few days, with defects in nearly all organs. Some organs normally have a few polyploid cells, with no adverse effects on health. Liver cells, for example, may be tetraploid (4 chromosome sets) or even octaploid (8 chromosome sets). Polyploidy is tolerable in some types of organisms. For example, many agriculturally important plants are polyploids.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.