10 Genetics, Cells, and Chromosomes 



plate, and the arms often extend away from the equator and 

 may frequently project into the cytoplasm. 



The metaphase chromosomes are thick, deeply staining struc- 

 tures. They frequently appear as rod-shaped, V-shaped, or J- 

 shaped bodies, and their particular appearance depends upon the 

 location of the centromere. If it is at the end {terminal attach- 



FiG. 3. Polar views of metaphase. (a) In the egg of the animal, Ascaris 

 megalocephala ; X775. (6) In cells of the root tip of Iris fulva; X1500. 

 Camera lucida drawings. 



nient) the chromosome will appear rod-shaped; if it is at or 

 very near the center {median or submedian attachment) it is 

 V-shaped; and if it is near but not at the end {subterminal 

 attachment) it has the shape of the letter J. The centromere 

 appears in the metaphase chromosome as a constriction. In 

 addition to the centromere, secondary constrictions may be 

 present near the end and may be very long and deep, so that 

 the end of the chromosome appears as a little knob, called a 

 satellite or trabant. The function of these secondary constric- 

 tions is not well known, but on some chromosomes they are 

 regions at which the chromosome is attached to the nucleolus 

 during the resting stage and from which the nucleolus begins 

 to form at telophase. Each metaphase chromosome still con- 

 sists of two chromatids but they are very close to one another 



