Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Peter A. Peterson


Transposable elements are thought to be responsible for creating genetic variation that is needed for evolution. The pervasiveness of transposable elements in certain breeding lines of maize suggests that part of the observed genetic variation in those lines might be the result of transposition activity. Stable genetic variation often results from the allelic differences created by footprints generated in the host genes upon element excision. Stable genetic variation can also result from insertions which are permanently fixed at a particular locus. The 1.3 kb I element of the a2-m1 (class II state) allele in maize is one example of a stable insertion. Though the I element never excises from the A2 gene it continues to interact with the TNPA (transposase A) product of En/Spm element. In the present study a test was designed to determine whether the continued interaction of the I element with TNPA would lead to excision of I or other change of this allele. The screening of 225,000 kernels did not yield any new states of the a2-m1 (class II state) allele in the presence of an active autonomous En/Spm element indicating that this I element is highly stable and permanently fixed at this locus despite the continued exposure of this element to the En/Spm transposase. This suggests that if new genetic variation is created by these stable inserts such variation would be very stable. Our results also imply that if an intron originates from a stable insert such intron acquisitions would also be stable. During the course of this work we have identified a dominant modifier of the M function of En/Spm. This modifier, named Modifier2, is similar to McClintock's Modifier1 in its genetic behavior and is assumed to be a deletion derivative of En/Spm element.



Digital Repository @ Iowa State University,

Copyright Owner

Vijayabhaskar Reddy Thatiparthi



Proquest ID


File Format


File Size

168 pages

Included in

Genetics Commons