Mitochondrial Restriction Fragment Length Polymorphism Research Articles

Impact of dried, creamed and cake supply formats on the genetic variation and ethanol tolerance of three Saccharomyces cerevisiae distilling strains

Scotch whisky fermentations typically employ high-gravity fermentation practices to maximize product formation and to minimize both energy and water inputs. This approach increases ethanol concentrations at the end of fermentation, creating stressful conditions for the yeast. In this work we examined the relative tolerance of four Saccharomyces cerevisiae distilling yeast strains, supplied in dried, creamed, cake or slurry format, to ethanol under CO2-induced anaerobic conditions. The cells were assessed for their capacity to recover and grow on inhibition spot plates and to maintain cell viability in ethanol-dosed suspensions. Variations in ethanol tolerance were observed between strains and between the same strain supplied in different formats. The creamed yeast format typically exhibited a higher tolerance to ethanol. One possible explanation for this observation is that cells surviving the dehydration and rehydration process might incur sub-lethal genome damage. Thus the genetic integrity of the most ethanol-tolerant strain was assessed as a function of supply format (two dried and one creamed). The mitochondrial DNA was examined using mitochondrial restriction fragment length polymorphism and the chromosomal DNA using pulsed field gel electrophoresis and polymerase chain reaction with both ITS and delta-specific primers. In one dried yeast sample, genetic integrity was compromised, highlighting the requirement for yeast intake quality assurance programmes. Copyright © 2012 The Institute of Brewing & Distilling

Contemporary gene flow between “paired” silver (Ichthyomyzon unicuspis) and northern brook (I. fossor) lampreys: implications for conservation

In most lamprey genera, “paired” species exist in which the larvae are morphologically similar or indistinguishable but, following metamorphosis, one species becomes parasitic while the other bypasses the adult feeding phase and rapidly becomes sexually mature. Since DNA barcoding and similar studies using short segments of the mitochondrial genome do not provide sufficient resolution to distinguish between recent divergence and a lack thereof, the current study examined the relationship between the parasitic silver lamprey (Ichthyomyzon unicuspis) and nonparasitic northern brook lamprey (I. fossor) using up to 10,230 bp from the mitochondrial genome to make phylogenetic inferences and mitochondrial restriction fragment length polymorphism (RFLP) and microsatellite markers to test for significant differences in allele frequencies. We found that silver and northern brook lampreys are not reciprocally monophyletic; two lineages were observed but each occurred within both species. There also were no significant range-wide differences in RFLP haplotype or microsatellite allele frequencies between the species, nor were there significant differences where they occurred sympatrically within the Lake Huron basin. Significant genetic differentiation was found only within the Lake Michigan basin where the results were potentially confounded by geographic separation. Our results thus support suggestions that silver and northern brook lampreys represent ecotypes of a single species since, where they are sympatric, they appear to be experiencing ongoing gene flow. However, alternative life history strategies can be important for a species’ long-term persistence, and critical data are needed to decide whether these two feeding types should be managed as a single unit.

Strategies to select yeast starters cultures for production of flavor compounds in cachaça fermentations

In this work, we have used classical genetics techniques to find improved starter strains to produce cachaça with superior sensorial quality. Our strategy included the selection of yeast strains resistant to 5,5',5″-trifluor-D: ,L: -leucine (TLF) and cerulenin, since these strains produce higher levels of higher alcohols and esters than parental strains. However, no clear relationship was observed when levels of flavoring compounds were compared with the levels expression of the genes (BAT1, BAT2, ATF2, EEB1 genes) involved with the biosynthesis of flavoring compounds. Furthermore, we determined the stability of phenotypes considered as the best indicators of the quality of the cachaça for a parental strain and its segregants. By applying the principal component analysis, a cluster of segregants, showing a high number of characteristics similar to the parental strain, was recognized. One segregant, that was resistant to TLF and cerulenin, also showed growth stability after six consecutive replications on plates containing high concentrations of sugar and ethanol. "Cachaça" produced at laboratory scale using a parental strain and this segregant showed a higher level of flavoring compounds. Both strains predominated in an open fermentative process through seven cycles, as was shown by mitochondrial restriction fragment length polymorphisms analysis. Based on the physical chemical composition of the obtained products, the results demonstrate the usefulness of the developed strategies for the selection of yeast strains to be used as starters in "cachaça" production.

Microsatellite and mitochondrial DNA markers show no evidence of population structure in walleye (Sander vitreus) in Lake Winnipeg

Walleye (Sander vitreus) are the main contributor to Manitoba's multi-million dollar commercial fishery, with Lake Winnipeg providing the largest and most profitable catch. In some systems, walleye show evidence of returning to the same spawning site each spring (i.e., philopatry), which can lead to the existence of multiple genetically-discrete spawning groups (i.e., stocks) within a lake. This study used nine microsatellite loci (N=932) and one mitochondrial restriction fragment length polymorphism assay (N=123) to investigate possible genetic divergence among walleye from 13 spawning sites in Lake Winnipeg, and compared these with those collected from two hatchery locations and other locations outside of Lake Winnipeg. Microsatellite loci resolved little population structure within Lake Winnipeg, with the exception of two sites (Grand Rapids and the Icelandic River), which showed low but significant levels of genetic divergence with most other sites (Fst=0.0066–0.0457). Slight to moderate genetic divergence was found between Lake Winnipeg walleye and sampling locations outside of Lake Winnipeg (Fst=0.0037–0.1054, P=0.0002). Mitochondrial DNA analysis indicated colonization of Lake Winnipeg by walleye from two glacial refugia (Missourian and Mississippian), but no population structure was detected among sites. The lack of stock structure found in Lake Winnipeg possibly indicates a low degree of natal philopatry, an amount of straying sufficient to obscure genetic structure, or obscured structure as a result of historical and current stocking. Overall genetic variation, using both mitochondrial and microsatellite markers, appeared comparable to that found in other walleye populations.

Genetic analysis of wandering albatrosses killed in longline fisheries off the east coast of New Zealand

1.Fisheries bycatch is an important global conservation issue. Each year many species, including seabirds, are killed accidentally in longline fisheries. Highly vagile marine species such as the wandering albatross species complex (Diomedea spp.), populations of which have declined dramatically due to fisheries-related mortality, traverse large areas of open ocean and as a result are at high risk of negative fisheries interactions. 2.For most wandering albatrosses found dead at-sea the provenance is unknown unless they are ringed, as their poor condition make species identification very difficult. However, molecular markers can be used as genetic tags to identify the population of origin of bycatch birds. 3.Five microsatellite markers and mitochondrial restriction fragment length polymorphism were used to genotype 41 individuals belonging to the wandering albatross species complex killed in longline fisheries in two locations off the east coast of the North and South Islands of New Zealand, an area known to be visited by at least three members of the wandering albatross groups. 4.Assignment tests indicate that the majority (22/30 of assigned individuals) of bycatch birds were D. antipodensis antipodensis from Antipodes Island, the closest breeding site. More than half of the North Island birds were assigned to D. a. antipodensis (8/14); the remaining samples were assigned to both the D. a. gibsoni from The Auckland Islands (n=3) and D. exulans from the South Atlantic/Indian Ocean (n=3). The South Island samples were almost exclusively assigned to D. a. antipodensis (14/16) of which 13 were males. In the North Island samples there were 14 males and 8 females. 5.This study has shown that molecular markers are a powerful tool to determine the species identity, population of origin and sex of bycatch birds to better understand the impact of fisheries-related mortality and conservation priorities for individual populations. Copyright © 2008 John Wiley & Sons, Ltd.

Concordant evolution of mitochondrial and nuclear genomes in the wheat pathogen Phaeosphaeria nodorum

We compared patterns of mitochondrial restriction fragment length polymorphism (RFLP) diversity with patterns of nuclear RFLP diversity to investigate the effects of selection, gene flow, and sexual reproduction on the population genetic structure and evolutionary history of the wheat pathogen Phaeosphaeria nodorum. A total of 315 fungal isolates from Texas, Oregon, and Switzerland were analyzed using seven nuclear RFLP probes that hybridized to discrete loci and purified mitochondrial DNA that hybridized to the entire mtDNA genome. Forty-two different mitochondrial haplotypes and 298 different nuclear haplotypes were detected. The two most frequent mtDNA haplotypes were present in every population and represented 32% of all isolates. High levels of gene flow, low levels of population subdivision, no evidence for either host specificity or cyto-nuclear disequilibrium were inferred from the analysis of both genomes. The concordance in estimates of these population genetic parameters from both genomes suggests that the two genomes experienced similar degrees of migration, genetic drift and selection.

Linking lakes? The population genetic structure of Chaoborus flavicans

Larvae of Chaoborus flavicans (Diptera: Chaoboridae) are common in various lakes and are important members of plankton communities. To assess gene flow between lakes, we sampled several populations throughout Europe. To explicitly test whether gene flow is higher within regions than between regions, we examined four regions each containing several populations. For a detailed analysis of regional gene flow, 12 populations within a region in North Germany were analysed. Allozymes and mitochondrial restriction fragment length polymorphism (RFLP) were used to estimate the relative amounts of gene flow. Results indicate that most of the dispersal in C. flavicans takes place between lakes within regions. Therefore, the population genetic structure of C. flavicans sets this species apart from other planktonic organisms, which are mainly passive dispersers and display low gene flow between lakes within regions. Consequently, these data are the first evidence that C. flavicans may form an important link between lakes within regions. Local adaptation within lakes may be decreased because of these processes, and the role of C. flavicans as a biomonitor of local lake conditions needs to be carefully reinvestigated.

Gene flow within and between regions: The population genetic structure of the phantom midge Chaoborus crystallinus (Diptera: Chaoboridae)

To determine the gene flow of Chaoborus crystallinus, populations throughout Europe were sampled. To test if the gene flow is higher within regions than between regions and to investigate if regional populations may act as metapopulations, four regions with several populations each were examined. For a detailed analysis of the regional gene flow, subregions within one region were analysed. Allozymes and mitochondrial restriction fragment length polymorphism (RFLP) were used to estimate the relative amounts of gene flow. On the European scale gene flow between populations within regions is higher than between regions. On the regional scale, gene flow between subregions is higher than between populations within subregions. Generally, the genetic differentiation between populations within regions is higher for the mitochondrial RFLP data than for the allozyme data. These results suggest that most of the dispersal is female dominated and mostly takes place between populations within regions. Due to this extensive regional gene flow, local adaptation may be influenced by regional processes. This might have interesting implications for the coevolution of the predator C. crystallinus and its plankton prey.

GENETIC VARIATION IN THE SPREAD OF DROSOPHILA SUBOBSCURA FROM A NONEQUILIBRIUM POPULATION

Drosophila subobscura was first identified in North America in the early 1980s, and a newer D. subobscura population in Utah appears to have been established more than 10 years later. In this study, we use nuclear microsatellite allele frequencies, mitochondrial restriction fragment length polymorphism (RFLP) allele frequencies, and computer simulations to investigate possible scenarios of how this species has spread across North America. Our method develops a 95% confidence interval for the maximum and minimum number of founders that could have colonized the new population given various scenarios for spread. Unlike many other methods, it may be applied to nonequilibrium source populations given certain conditions. We find that observed allele frequency differences between newer and older D. subobscura populations are consistent with very few inseminated females being transported east from the coast in a single step or with larger numbers of colonizers invading after several intermediate steps. They are not consistent with a large, panmictic population of D. subobscura colonizing Utah in a single step.

GENETIC VARIATION IN THE SPREAD OF DROSOPHILA SUBOBSCURA FROM A NONEQUILIBRIUM POPULATION

Drosophila subobscura was first identified in North America in the early 1980s, and a newer D. subobscura population in Utah appears to have been established more than 10 years later. In this study, we use nuclear microsatellite allele frequencies, mitochondrial restriction fragment length polymorphism (RFLP) allele frequencies, and computer simulations to investigate possible scenarios of how this species has spread across North America. Our method develops a 95% confidence interval for the maximum and minimum number of founders that could have colonized the new population given various scenarios for spread. Unlike many other methods, it may be applied to nonequilibrium source populations given certain conditions. We find that observed allele frequency differences between newer and older D. subobscura populations are consistent with very few inseminated females being transported east from the coast in a single step or with larger numbers of colonizers invading after several intermediate steps. They are not consistent with a large, panmictic population of D. subobscura colonizing Utah in a single step.Corresponding Editor: K. Ross

Mitochondrial restriction fragment length polymorphism (RFLP) and sequence variation among closely related avian species and the genetic characterization of hybrid Dendroica warblers.

To address several interconnected goals, we used mitochondrial DNA (mtDNA) sequences to explore evolutionary relationships among four potentially hybridizing taxa in a North American avian superspecies (Dendroica occidentalis, D. townsendi, D. virens, and D. nigrescens). We first compared the results of a previous restriction fragment length polymorphism (RFLP)-based study with 1453 nucleotides from the mitochondrial cytochrome oxidase subunit I (COI), ATP-synthase 6 (ATPase 6), and ATP-synthase 8 (ATPase 8) genes. Separate phylogenetic analyses of the RFLP and sequence data provided identical and well-supported hierarchical species-level reconstructions that grouped occidentalis and townsendi as sister taxa. We then explored several general features of mitochondrial evolution via a comparison of the RFLP and sequence data sets. Qualitative rate differences that seemed evident in highly autocorrelated comparisons of RFLP vs. sequence pairwise distances were not supported when autocorrelation was removed. We also noted a high variance in corresponding RFLP and sequence distances after the removal of autocorrelation effects. This variance suggests that caution should be used when combining RFLP and sequence-based data in studies that require the large-scale synthesis of divergence estimates drawn from sources employing different molecular techniques. Finally, we used our parallel RFLP and sequence data to design and validate a rapid and inexpensive polymerase chain reaction-RFLP (PCR-RFLP) protocol for determining species-specific mitochondrial haplotypes. This PCR-RFLP technique will be applied in ongoing studies of the occidentalis/townsendi hybrid zone, where the historic and geographical complexity of the interbreeding populations necessitates the genotyping of thousands of individual warblers.

Genetic markers Genealogies and Biogeographic patterns in the Cladocera

Cladoceran crustaceans are an important component of zooplankton in a wide range of freshwater habitats. Although the ecological characteristics of several cladoceran species have been well studied, biogeographical studies have been hampered by problematic taxonomic affiliations. However, recently developed molecular techniques, provide a powerful tool to subject aquatic taxa to comparative analyses. Here we highlight recent molecular approaches in aquatic ecology by presenting a simple method of DNA preparation and PCR amplification of the mitochondrial DNA (16S rDNA) in species from nine different families within the cladocera. On a broad taxonomic scale, sequence analysis of this mtDNA fragment has been used to produce the first molecular based phylogeny of the cladocera. This analysis clustered the cladoceran families in a fashion similar to that suggested by previous systematic classifications. In a more detailed analysis of the family Daphniidae, nuclear randomly amplified polymorphic DNA (RAPD), mitochondrial restriction fragment length polymorphism (RFLP) and morphological analyses were combined to identify species and interspecific hybrids within the Daphnia galeata species complex across 50 lakes in 13 European countries and one lake in Africa. The study revealed interspecific hybridization and backcrossing between some taxa (D. cucullata and D. galeata) to be widespread, and species and hybrids to frequently occur in sympatry. Genetic, as well as morphological information, suggests the occurrence of D. hyalina outside the Holarctic.

Analysis of genetic diversity in common loon Gavia immer using RAPD and mitochondrial RFLP techniques

We used random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphisms (RFLP) of mitochondrial cytochrome b (cyt b) gene to evaluate the genetic diversity in common loon Gavia immer populations from two regions in the United States: New England (NE) and Michigan (MI). RAPD analysis with 18 primers showed 74% polymorphism in NE and 50% in MI loons (similarity coefficient F= 0.92). Although no population‐specific markers were found, the frequencies of some RAPD bands varied between the two populations suggesting geographical differences. RFLP analyses with BamHI enzyme and a 307‐bp mitochondrial cyt b gene showed four haplotypes in the NE loon samples and two in the MI samples. The mtDNA haplotype diversity was 0.74 for NE and 0.51 for MI loons, supporting the RAPD data that NE loons have greater genetic diversity than MI loons.

Genotypes at the GluR6 kainate receptor locus are associated with variation in the age of onset of Huntington disease.

Huntington disease (HD) is associated with abnormal expansions of a CAG repeat close to the 5' end of the IT15 gene. We have assembled a set of 293 HD subjects whose ages of onset were known and sized their HD CAG repeats. These repeats accounted for 69% of the variance of age of onset when we used the most parsimonious model, which relates the logarithm of age of onset to a function of CAG repeat number. Since other familial factors have been proposed to influence the age of onset of HD, we have examined a number of candidate loci. The CAG repeat number on normal chromosomes, the delta2642 polymorphism in the HD gene, and apolipoprotein E genotypes did not affect the age of onset of HD. Although mitochondrial energy production defects in HD have led to suggestions that variants in the mitochondrial genome may be associated with clinical variability in HD, this suggestion was not supported by our preliminary experiments that examined the DdeI mitochondrial restriction fragment length polymorphism at position 10,394. Excitotoxicity has been a favored mechanism to explain the cell death in HD, particularly since intrastriatal injection of excitatory amino acids in animals creates HD-like pathology. Accordingly, we investigated the GluR6 kainate receptor. Of the variance in the age of onset of HD that was not accounted for by the CAG repeats, 13% could be attributed to GluR6 genotype variation. These data implicate GluR6-mediated excitotoxicity in the pathogenesis of HD and highlight the potential importance of this process in other polyglutamine repeat expansion diseases.

Resolution of recent radiations within three evolutionary lineages of felidae using mitochondrial restriction fragment length polymorphism variation

Patterns of mitochondrial restriction fragment length polymorphism (RFLP) variation were used to resolve more recent relationships among the species of the Felidae ocelot lineage, domestic cat lineage, and pantherine lineage. Twenty-five of 28 restriction enzymes revealed site variation in at least 1 of 21 cat species. The ocelot lineage was resolved into three separate sistertaxa groups: Geoffroy's cat (Oncifelis geoffroyi) and kodkod (O. guigna), ocelot (Leopardus pardalis) and margay (L. wiedii), and pampas cat (Lynchailurus colocolo) and most of the tigrina samples (Leopardus tigrina). Within the domestic cat lineage, domestic cat (Felis catus), European wild cat (F. silvestris), and African wild cat (F. libyca) formed a monophyletic trichotomy, which was joined with sand cat (F. margarita) to a common ancestor. Jungle cat (F. chaus) and black-footed cat (F. nigripes) mtDNAs diverged earlier than those of the other domestic cat lineage species and are less closely related. Within the pantherine lineage, phylogenetic analysis identified two distinct groups, uniting lion (P. leo) with leopard (P. pardus) and tiger (P. tigris) with snow leopard (P. uncia).

Fate of Parasite and Host Organelle DNA during Cellular Transformation of Red Algae by Their Parasites.

The transfer of a nucleus into a cytoplasm of a genetically foreign cell and its subsequent multiplication in the cytoplasm of this cell characterize most parasitic red algal species and their interactions with specific red algal hosts. Nuclei enter the host's cytoplasm upon cell fusion of parasite and host cell; here, they replicate, are spread to contiguous host cells, and ultimately are packaged into spores that reinfect other host thalli. In this study, we examined whether the proplastids and mitochondria that occur in these red algal adelphoparasites are acquired from their host or whether they are unique to the parasite and are brought into the host along with the parasite nucleus. To establish their origins and fates, plastid and mitochondrial restriction fragment length polymorphisms (RFLPs) of parasite cells were compared with those of their host plastid and mitochondrial DNA in three host and parasite pairs. For plastids, no RFLP differences were found between hosts and parasites, supporting an earlier conclusion, based on microscopic studies, that the proplastids of parasites are acquired from their hosts. For mitochondria, characteristic RFLP differences were detected between host and parasite for two of the pairs of species but not for the third. Evidence of the evolutionary difference between hosts and their parasites was shown by RFLP differences between nuclear ribosomal repeat regions.

Comparing the Resynthesis of Brassica napus L. by Interspecific Somatic and Sexual Hybridization. II. Hybrid Morphology and Identifying Organelle Genomes

Brassica napus (genome aacc), a natural allotetraploid derived from hybridization between B. oleracea L. (genome cc) and B. rapa L. (genome aa), was resynthesized by somatic and sexual hybridization. Seventy-two interspecific somatic (R0) hybrids and 27 sexual (F1) hybrids were produced from the same parent plants. R0 and F1 hybrids displayed morphology that was intermediate to the species parents, but B. rapa characteristics tended to predominate. R0 hybrids with nuclear DNA content equivalent to natural B. napus were uniform for nuclear-encoded traits, whereas allotetraploid F1 hybrids were variable for traits such as morphology, flower color, and seed production. Chloroplast restriction fragment length polymorphisms (RFLPs) showed unequal segregation in the R0 population favoring the chloroplasts of B. rapa; two of the 58 R0 hybrids tested had only the B. oleracea marker and 10 contained markers of both parents. Mitochondrial RFLPs showed a similar bias among the 56 R0 hybrids tested; only four plants showed B. oleracea markers exclusively, and the remaining plants were evenly distributed between having only B. rapa markers or having combinations from both species. In contrast, sexual hybrids displayed only maternal organelle markers.

An Assessment of Genetic Relationships between Members of the Phytophthora megasperma Complex and Phytophthora vignae using Molecular Markers

Genetic relationships between Phytophora megasperma f. sp. glycinea (Pmg) and morphologically similar taxa, P. megasperma f. sp. medicaginis (Pmm), P. megasperma f. sp. trifolii (Pmt), P. megasperma from Douglas Fir (PmDF) and asparagus (PmAS) and Phytophthora vignae, were explored by restriction fragment length polymorphism (RFLP) analysis of nuclear DNA using random genomic multi-copy, cDNA, and ribosomal DNA probes as well as random amplified polymorphic DNA (RAPDs) and RFLP analysis of ribosomal intergenic spacer regions amplified by the polymerase chain reaction (PCR). Each method detected large differences between these taxa and P. megasperma f. sp. glycinea. P. vignae was more closely related to P. megasperma f. sp. glycinea than the other taxa on the basis of the cDNA RFLPs and RFLPs of PCR amplified rDNA intergenic spacer regions. We conclude that each of the taxa examined represent separate species. This supports the most recent reclassification based on mitochondrial RFLPs and electrophoretic protein patterns of the host-specific taxa to P. sojae (Pmg), P. trifolii (Pmt) and P. medicaginis (Pmm).

The Molecular Basis of Genetic Diversity among Cytoplasms of Triticum and Aegilops. VIII. Mitochondrial RFLP Analyses Using Cloned Genes as Probes

Restriction fragment length polymorphisms (RFLPs) among mtDNA digests of Triticum and Aegifops species have been analyzed by Southern blot hybridization with four cloned mitochondrial genes as probes. Three Triticum and 14 ( 16 sources, in total) Aegilops species have been studied. These represent the three wheat groups Einkorn, Dinkel, and Timopheevi and all six Aegilops sections (Polyeides, Cylindropyrum, Vertebra@ Sitopsis, Amblyopyrum, and Comopyrum) . Hybridization patterns of eight restriction-enzyme /probe combinations (BumHIor HindIIIdigested mtDNAs probed with four mtDNA clones, each containing one of the four genes atpA, coxll, rrn18&5, or rrn26) were examined. With all of the probes used, mtDNA from one source of Ae. speltoides showed hybridization profiles identical to those of T. timopheevi, and mtDNA from Ae. searsii gave profiles identical to those of Ae. kotschyi. Otherwise, different hybridization profiles were found among all mtDNAs, giving 19 mtDNA samples classifiable into 17 different types. Based on the percentages of common fragments among all pairs of mtDNAs, a phylogenetic tree of mitochondrial genomes was generated by the UPGMA method. The resultant tree showed that the mitochondrial genomes of Triticum and Aegilops have differentiated into three major groups: ( 1) T. monococcum, (2) Ae. speltoides and polyploid wheats, and (3) all other species. The hybridization patterns also revealed differences in copy numbers of all mitochondrial genes, although the extent of polymorphisms differed with the different probes. Stoichiometric fragments of one accession often corresponded to substoichiometric fragments of other accessions, suggesting quantitative, rather than qualitative, differentiation of mitochondrial genomes among accessions.

Transmission of mitochondrial DNA in Ustilago violacea.

Mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) were used as genetic markers for following mitochondrial transmission in the basidiomycete Ustilago violacea. Yeast-like cells of opposite mating types (a1 and a2) were mated on 2% water agar and were treated with alpha-tocopherol to induce formation of dikaryotic hyphae. Upon depletion of the alpha-tocopherol, the hyphae budded off haploid cells with parental nuclear genotypes. These cells were examined for mitochondrial RFLP phenotype. In progeny expressing the a1 mating type, mitochondria from either parent were observed equally frequently. In progeny with the a2 mating type, mitochondria were almost exclusively (94%) from the a2 parent.