Female-dependent transmission of paternal mtDNA is a shared feature of bivalve species with doubly uniparental inheritance (DUI) of mitochondrial DNA

Several species from a number of bivalve molluscan families are known to have a paternally transmitted mitochondrial genome, along with the standard maternally transmitted one. The main characteristic of the phenomenon, known as doubly uniparental inheritance (DUI), is the coupling of sex and mtDNA inheritance: males receive both genomes but transmit only the paternal to their progeny; females either do not have the paternal genome or, if they do, they do not transmit it to their progeny. In the families Mytilidae and Veneridae, both of which have DUI, a female individual is either female-biased (it produces only, or nearly so, female progeny), male-biased (it produces mainly male progeny) or non-biased (it produces both genders in intermediate frequencies). Here we present evidence for a same pattern in the freshwater mussel, Unio delphinus (Unionidae). These results suggest that the maternal control of whether a fertilized egg will develop into a male or a female individual (and the associated feature of whether it will inherited or not inherit the paternal mtDNA) is a general characteristic of species with DUI.Peer reviewe

Genetic structuring in farmed and wild Gilthead seabream and European seabass in the Mediterranean Sea: implementations for detection of escapees

Microsatellite markers were used to investigate the genetic structure of the two most important cultured fish in the Mediterranean Sea, the gilthead seabream (Sparus aurata) and the European seabass (Dicentrarchus labrax), from two (one wild and one farmed) populations in Western Mediterranean (Spain) and from two (one wild and one farmed) populations Eastern Mediterranean (Greece). All populations were in Hardy-Weinberg disequilibrium. Interestingly, wild and farmed populations for both species from Greece were genetically differentiated and could be distinguished from each other. We used Bayesian methods for cluster analysis of farmed and wild populations. Our analysis has implications for the identification of escapees from fish farms to the wild

Searching for sequence directed mutagenesis in eukaryotes.

Sequence directed mutagenesis is a mechanism by which imperfect repeats ¿repair¿ each other to become perfect, generating mutations. This process is known to be prevalent in prokaryotes and it has been implicated in several human genetic diseases. Here we test whether sequence directed mutagenesis occurs in the protein coding sequences of eukaryotes using extensive DNA sequence data from humans, mice, Drosophila, nematodes, yeast, and Arabidopsis. Using two tests we find little evidence of sequence directed mutagenesis. We conclude that sequence directed mutagenesis is not prevalent in eukaryotes and that the examples of human diseases, apparently caused by sequence directed mutagenesis, are probably coincidental

Searching for doubly uniparental inheritance of mtDNA in the apple snail Pomacea diffusa

Doubly uniparental inheritance (DUI) of mitochondrial DNA (mtDNA) is an exceptional mode of mtDNA transmission, restricted so far to the class of bivalves. We searched for DUI outside bivalves using the apple snail Pomacea diffusa. It was an appropriate candidate to search for DUI for three reasons; it belongs to gastropods, which is the closest sister group to bivalves, it is gonochoristic and it has a strong sex bias in the progeny of different female individuals. These phenomena (gonochorism and sex-biased progeny) are also found in species with DUI. We searched for heteroplasmy in males and for high sequence divergence among mtDNA sequences obtained from male and female gonads. All sequences examined were identical. These data suggest that the mtDNA in P. diffusa is maternally transmitted and DUI remains an exclusive characteristic of bivalvesPeer reviewe

NUMTs Can Imitate Biparental Transmission of mtDNA—A Case in Drosophila melanogaster

mtDNA sequences can be incorporated into the nuclear genome and produce nuclear mitochondrial fragments (NUMTs), which resemble mtDNA in their sequence but are transmitted biparentally, like the nuclear genome. NUMTs can be mistaken as real mtDNA and may lead to the erroneous impression that mtDNA is biparentally transmitted. Here, we report a case of mtDNA heteroplasmy in a Drosophila melanogaster DGRP line, in which the one haplotype was biparentally transmitted in an autosomal manner. Given the sequence identity of this haplotype with the mtDNA, the crossing experiments led to uncertainty about whether heteroplasmy was real or an artifact due to a NUMT. More specific experiments revealed that there is a large NUMT insertion in the X chromosome of a specific DGRP line, imitating biparental inheritance of mtDNA. Our result suggests that studies on mtDNA heteroplasmy and on mtDNA inheritance should first exclude the possibility of NUMT interference in their data

Genetic characterization of Albanian grapevine cultivars by microsatellite markers

A recently restored ampelographic collection of Albanian grapevine accessions has been submitted to genetic profiling with eleven nuclear microsatellite markers, widely used in other studies. Microsatellite profiling resulted in 28 single profiles for 29 accessions. Two cultivars, Shesh I bardhë and Pucalla, were found to be synonyms. Genetic profiles of Albanian cultivars were compared at 8 microsatellite loci to 29 most commonly cultivated Greek cultivars. Albanian cultivars were found to be more closely related to Greek cultivars from Peloponnese. One Greek cultivar named Dempina was found to be genetically close to two Albanian cultivars Debina teki and Debina kala, which are homonyms Another cultivar, known as Toska or Sinambel displayed a tri-allelic profile at 5 loci over 10 analysed loci. Such a high number of tri-allelic loci found in one individual favours the hypothesis of triploidy but the chimerism hypothesis cannot be excluded without further work

The Excess of Small Inverted Repeats in Prokaryotes

Recent analyses have shown that there is a large excess of perfect inverted repeats in many prokaryotic genomes but not in eukaryotic ones. This difference could be due to a genuine difference between prokaryotes and eukaryotes or to differences in the methods and types of data analyzed ¿ full genome versus protein coding sequences. We used simulations to show that the method used previously tends to underestimate the expected number of inverted repeats. However, this bias is not large and cannot explain the excess of inverted repeats observed in real data. In contrast, our method is unbiased. When both methods are applied to bacterial protein coding sequences they both detect an excess of inverted repeats, which is much lower than previously reported in whole prokaryotic genomes. This suggests that the reported large excess of inverted repeats is due to repeats found in intergenic regions. These repeats could be due to transcription factor binding sites, or other types of repetitive DNA, on opposite strands of the DNA sequence. In contrast, the smaller, but significant, excess of inverted repeats that we report in protein coding sequences may be due to sequence-directed mutagenesis (SDM). SDM is a process where one copy of a small, imperfect, inverted repeat corrects the other copy via strand misalignment, resulting in a perfect repeat and a series of mutations. We show by simulation that even very low levels of SDM, relative to the rate of point mutation, can generate a substantial excess of inverted repeats