STUDIES OF A MITOTICALLY STABLE DUPLICATION STRAIN OF ASPERGILLUS NIDULANS

Abstract

A strain of the ascomycete, Aspergillus nidulans, has been produced which showed a peculiar phenotype. It produced perithecia profusely and spontaneously at 37°c and exhibited meiotic segregation when selfed. Genetic analyses showed that this strain had a segment of chromosome I in duplicate on chromosome II, and a small segment of chromosome VI in duplicate on chromosome VIII. It also had a segment of chromosome VI translocated to chromosome VIII. Spontaneous perithecia production was found to be directly linked to the duplication of the segment of chromosome VI and this ability to produce perithecia spontaneously was lost with the loss of this duplicated segment, The loss of this duplication was of a high order in the meiotic process and was found to be responsible for meiotic segregation in the selfed perithecia of this strain, The vegetative loss of this duplication was found to be of a low frequency but can be induced to a higher frequency by the use of caffeine. The strain studied was also found to be highly stable vegetatively and thought to be unusual for a strain with two duplication systems, The duplication of the segment of chromosome I was found to be highly unstable when it existed alone. The duplication of the segment of chromosome VI would appear to stabilise the other duplication in the strain studied, even though it was itself unstable in a small degree when it existed alone. The instability of the duplication of the segment of chromosome I was enhanced when the duplication of the segment of chromosome VI was lost but with VI - VIII translocation remaining.