Originally published as Genetics Published Articles Ahead of Print on January 16, 2005.

Genetics, Vol. 169, 1311-1327, March 2005, Copyright © 2005
doi:10.1534/genetics.104.033167

Chromosome Loss Followed by Duplication Is the Major Mechanism of Spontaneous Mating-Type Locus Homozygosis in Candida albicans

Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242

1 Corresponding author: Department of Biological Sciences, 302 BBE, University of Iowa, Iowa City, IA 52242.
E-mail: david-soll{at}uiowa.edu

Candida albicans, which is diploid, possesses a single mating-type (MTL) locus on chromosome 5, which is normally heterozygous (a/{alpha}). To mate, C. albicans must undergo MTL homozygosis to a/a or {alpha}/{alpha}. Three possible mechanisms may be used in this process, mitotic recombination, gene conversion, or loss of one chromosome 5 homolog, followed by duplication of the retained homolog. To distinguish among these mechanisms, 16 spontaneous a/a and {alpha}/{alpha} derivatives were cloned from four natural a/{alpha} strains, P37037, P37039, P75063, and P34048, grown on nutrient agar. Eighteen polymorphic (heterozygous) markers were identified on chromosome 5, 6 to the left and 12 to the right of the MTL locus. These markers were then analyzed in MTL-homozygous derivatives of the four natural a/{alpha} strains to distinguish among the three mechanisms of homozygosis. An analysis of polymorphisms on chromosomes 1, 2, and R excluded meiosis as a mechanism of MTL homozygosis. The results demonstrate that while mitotic recombination was the mechanism for homozygosis in one offspring, loss of one chromosome 5 homolog followed by duplication of the retained homolog was the mechanism in the remaining 15 offspring, indicating that the latter mechanism is the most common in the spontaneous generation of MTL homozygotes in natural strains of C. albicans in culture.




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