a. A chromosome is a very long double-helix thread of DNA. Thus, each chromosome consists of a large number of genes. The genes have very specific locations along the length of each chromosome. Recently, researchers have been able to identify specific sequences of genes along a chromosome and illustrate the sequences with gene maps.
b. Except during cell division, chromosomes are observed as granules of chromatin material within the cell nucleus. During the process of cell division, this chromatin material aggregates so that it may be identified as one of the 46 individual chromosomes found in each human cell (diploid condition).
c. These 46 chromosomes of the human cell occur in pairs. Thus, we may say that there are two sets, with 23 chromosomes in each set.
Of the 23 different chromosomes, 22 deal with the body in general and are called autosomal chromosomes. The last chromosome is called the sex chromosome. There are two kinds of sex chromosomes--X and Y. When an individual's cells each have two X chromosomes (XX), the individual is genetically a female. On the other hand, when an individual's cells each have one X and one Y chromosome (XY), that individual is genetically a male.
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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.