Genetic and environmental factors affecting mating type frequency in natural isolates of Tetrahymena thermophila.
In Tetrahymena thermophila mating type alleles specify temperature sensitive frequency distributions of multiple mating types. A-like alleles specify mating types I, II, III, V and VI, whereas B-like alleles specify mating types II through VII. We have characterized the mating type distributions specified by several A- and B-like genotypes segregated by genomic exclusion from cells isolated from a pond in northwestern Pennsylvania. The B-like genotypes are alike in specifying very low frequencies of mating type III, but differ with respect to the frequencies of other mating types, particularly II and VII. An A-like genotype specifies a high frequency of mating type III and is unstable in successive generations for the expression of mating type II, suggesting a possible modifier. Inter se crosses performed at 18 degrees C, 28 degrees C and 34 degrees C showed that each genotype specifies a frequency distribution that is uniquely affected by temperature. No mating type was affected the same way by temperature in all genotypes. In A/B heterozygotes, the B-like genotype exhibited partial dominance. The genotypes described here differ significantly from previously described genotypes from the same pond, indicating that there are numerous mating type alleles. For frequency-dependent selection to equalize mating type frequencies, it must act not only on complex multiple alleles but also on the response of mating type alleles to temperature.
Arslanyolu
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Department of Biological, Geological and Environmental Sciences, Cleveland State University, Ohio 44115, USA.
Doerder
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FP
D000483:Alleles; D000818:Animals; D005618:Fresh Water / Q000469:parasitology*; D005787:Gene Frequency; D005828:Genetics, Population; D018503:Genome, Protozoan; D006579:Heterozygote; D006720:Homozygote; D012098:Reproduction / Q000235:genetics / Q000502:physiology; D013696:Temperature; D016808:Tetrahymena thermophila / Q000235:genetics* / Q000502:physiology*