. Principles of modern biology. Biology. 508 - Heredity and Evolution fill II n %. Id K K ft A 6 A h Y Fig. 26-27. Diploid set of chromosomes in man, derived from a cell at metaphase. By this time each chromosome has undergone replication, but a complete separation of the sister replicas has not oc- curred. Selection of the paired members requires a precise study of the morphology, including the centromere (constricted point) positions, of the randomly arranged chromosomes of an original prepara- tion (lower left of photo), utilizing a magnification considerably higher than is shown h
. Principles of modern biology. Biology. 508 - Heredity and Evolution fill II n %. Id K K ft A 6 A h Y Fig. 26-27. Diploid set of chromosomes in man, derived from a cell at metaphase. By this time each chromosome has undergone replication, but a complete separation of the sister replicas has not oc- curred. Selection of the paired members requires a precise study of the morphology, including the centromere (constricted point) positions, of the randomly arranged chromosomes of an original prepara- tion (lower left of photo), utilizing a magnification considerably higher than is shown here. Then the paired members are arranged and numbered, forming what is called a karyotype, which may be nor- mal or abnormal. (Courtesy of Alexander G. Beam, The Rockefeller Institute, New York.) condition include a malformation of the tongue and a very severe retardation of growth, both physical and mental. The Klinefelter and Turner syndromes both are related to abnormalities in the sex chromosomes. The Klinefelter patient is always a male with an XXY constitution. Typically the stature is tall, and usually some degree of mental deficiency is present. Sperm production is reduced to the point of virtual sterility and the breasts show a tend- ency toward overdevelopment. The Turner patient, on the other hand, lacks a Y chromo- some; that is. the genetic constitution is XO. The condition is associated with malforma- tions of the aorta, deafness, shortness of stature, and some degree of mental retarda- tion. Other Aspects of Human Inheritance. Most normal differences among human indi- ct viduals—such as size, weight, color of skin, hair, and eyes—are, as in other animals, in- fluenced by many genes; and there are no very closelv inbred stocks in man. All human individuals arc heterozygous for many genes, and consequently it is difficult to forecast the precise distribution of most characteristics among human offspring. Moreover, many characteristics—such as height and weig
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