Inversion 401 



at first prophase and no dicentric bridge chromatids or frag- 

 ments are present at either the first or second anaphase. Only 

 two differences may be observed between an inversion homozy- 

 gote and the original stock. In the first place, the linear order 

 of the genes in the chromosome bearing the inversion is not the 



Fig. 107. Dicentric chromatids in microspores of Tradescantia following 

 treatment with X-rays, (a) T. gigantea; two bridges with balanced frag- 

 ments at anaphase following radiation during the resting stage preceding 

 the microspore division, (b) T. sp,; anaphase showing aberration produced 

 bj'- one hit at prophase; one chromatid bridge and a partly straightened 

 U-shaped fragment are present, (c) Metaphase showing a dicentric chro- 

 mosome and an accompanying fragment; this is a two-hit chromosome 

 aberration, {d) Anaphase showing the behavior of dicentric chromosomes. 

 {h, c, and d courtesy of Dr. Sax in Genetics; a, original.) 



same throughout as in the original chromosome, for the genes in 

 the inverted segment are in reverse order with respect to the 

 remainder of the chromosome. Consequently, the linkage map 

 of the chromosome with the inversion is different from the map 

 in the original. In the second place, because of the inversion, 

 genes lie next to a different region of the chromosome from the 

 original one. This change in position may cause one or more 

 of those genes to produce a new phenotype. The meiotic be- 

 havior of the plant or animal with the homozygous inversion is 



